HSC CHEMISTRY
INVESTIGATIONS
>ÀÞÊ-V
iÊUÊ >À}>ÀiÌÊ}>
Thanks to Oatley campus of Georges River College for the use of equipment to photograph.
© Science Press 2009 First published 2009 Science Press Private Bag 7023 Marrickville NSW 1475 Australia Tel: (02) 9516 1122 Fax: (02) 9550 1915
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All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of Science Press. ABN 98 000 073 861
Contents Introduction
v
Verbs to Watch
vi
Dot Points Production of Materials
vii
The Acidic Environment
ix
Chemical Monitoring and Management
xi
Industrial Chemistry
xiii
Shipwrecks, Corrosion and Conservation
xv
Investigations Production of Materials
1
The Acidic Environment
63
Chemical Monitoring and Management
137
Industrial Chemistry
197
Shipwrecks, Corrosion and Conservation
261
Appendix Answers
312
Data Sheet
318
Periodic Table
319
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Dot Point HSC Chemistry Investigations
Introduction This book contains all the instructions and other information needed for you to carry out the mandatory firsthand investigations listed in column 3 of the Board of Studies Chemistry syllabus. In some cases more than one experiment has been suggested. The syllabus requires 35 hours of practical work, but this need not all be experimental work. First-hand investigations include research to gather, process and analyse information, the presentation of information in written or spoken format and the solving of problems. In completing the activities in this book, you will have satisfied these aspects of the practical work required by the syllabus as detailed in column 3 of the syllabus document. Note that answers to practical and research exercises have not been provided as this would void the experimentation and research that you need to do in order to get these answers. Additional extension questions have been provided, where applicable, to encourage higher-order thinking and enable deeper understanding of chemistry concepts. Further examples of questions relevant to firsthand investigations in column 3 of the syllabus are included in two other books in this series, Dot Point HSC Chemistry and Dot Point HSC Chemistry Multiple Choice. The dot point numbers allocated to each experiment reflect the numbers allocated to that dot point in the other books in this series. Remember that these numbers are author derived and do not appear in the syllabus. Wherever possible, allowance has been made for variations in experimental method. This is necessary because schools have access to different resources and teachers often wish to design their own activities specific to their resources. Also, you are expected to develop skills in the planning of experiments and if you are always given ‘recipes’ you will never learn to do this. However, as many students struggle when it comes to planning and writing up experiments and research, many hints are provided. Experimental and research work is an integral part of the study of Chemistry. It is not meant to stand alone. You should always look for the relevance of your experimental and research work to the topic being studied. Thus it is recommended that after you carry out these activities, and your teacher has checked your work, the completed sheets should be inserted in the appropriate place in your notes. This book is NOT a series of ‘chemical recipes’ or a ‘how to do it’ manual. It is designed to help you record and evaluate experimental procedures that you will design and carry out during the Chemistry course and to encourage you to see the significance of information obtained from practical activities and research. Before you carry out any experimental procedure it is essential that you consult Safety Data Sheets and information from your teacher and textbooks in order to find out the risks associated with using any chemicals involved and precautions needed to deal with these risks. Before commencing any practical work, you must discuss with your teacher the necessary precautions for dealing with the chemicals and equipment to be used. All aspects of your experimental design must be approved by your teacher.
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Introduction
Verbs to Watch account/account for State reasons for, report on, give an account of, narrate a series of events or transactions.
distinguish Recognise or note/indicate as being distinct or different from, note difference between things.
analyse Identify components and the relationships among them, draw out and relate implications.
evaluate Make a judgement based on criteria. examine Inquire into.
apply Use, utilise, employ in a particular situation.
explain Relate cause and effect, make the relationship between things evident, provide why and/or how.
appreciate Make a judgement about the value of something.
extract Choose relevant and/or appropriate details.
assess Make a judgement of value, quality, outcomes, results or size.
extrapolate Infer from what is known.
calculate Determine from given facts, figures or information.
identify Recognise and name.
clarify Make clear or plain.
interpret Draw meaning from.
classify Arrange into classes, groups or categories.
investigate Plan, inquire into and draw conclusions about.
compare Show how things are similar and different.
justify Support an argument or conclusion.
construct Make, build, put together items or arguments.
outline Sketch in general terms; indicate the main features.
contrast Show how things are different or opposite.
predict Suggest what may happen based on available data.
critically (analyse/evaluate) Add a degree or level of accuracy, depth, knowledge and understanding, logic, questioning, reflection and quality to an analysis or evaluation.
propose Put forward (a point of view, idea, argument, suggestion etc) for consideration or action.
deduce Draw conclusions.
recall Present remembered ideas, facts or experiences.
define State the meaning of and identify essential qualities.
recommend Provide reasons in favour.
demonstrate Show by example.
recount Retell a series of events.
describe Provide characteristics and features.
summarise Express concisely the relevant details.
discuss Identify issues and provide points for and against.
synthesise Put together various elements to make a whole.
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Production of Materials Dot Point 1. 1.3
Page
Page
4.
Energy from redox reactions
4.1
First-hand investigation: Galvanic cells.
41
4.2
First-hand investigation: Potential difference of metals in an electrolyte.
45
11
4.9
Calculations using the redox table.
49
4.10 Chemistry and uses of batteries compared.
53
Energy and raw materials from fossil fuels First-hand investigation: Alkanes and alkenes with bromine.
3
1.7
Modelling polymerisation.
9
2.
Materials from biomass
2.2
Development and use of a biopolymer.
3.
Ethanol – use and manufacture
3.3
Modelling the dehydration and hydrolysis of ethylene.
15
3.4
Industrial production of ethanol from sugar cane.
19
First-hand investigation: Molar heats of combustion of alkanols.
23
3.8
Dot Point
3.10 Ethanol as a car fuel.
31
3.12 First-hand investigation: Fermentation of glucose.
35
5.
Nuclear chemistry
5.2
Recent discoveries of elements.
57
5.8
Radioisotopes – benefits and problems.
59
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Production of Materials
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The Acidic Environment Dot Point
Page
Dot Point
Page
4.
Acid/base theories
4.1
Using secondary sources.
107
4.6
First-hand investigation: pH of salt solutions.
109
1.
Indicators
1.1
First-hand investigation: Natural indicators.
65
1.2
Indicators – colour changes.
71
1.5
Acidic/basicity of household substances.
73
4.11 First-hand investigation: Titrations.
113
4.12 First-hand investigation: Titration of a domestic substance using computer-based technology.
125
4.13 Neutralisation in accidents.
129
2.
Acidic oxides and the atmosphere
2.7
First-hand investigation: Decarbonation of a soft drink.
75
2.12 Industrial origins of oxides of sulfur and nitrogen.
81
3.
Acids and pH
3.1
First-hand investigation: Using pH meters or probes
85
3.4
Naturally occurring acids and bases.
91
3.7
Strong and weak acids.
93
3.8
Ionic equations for acid ionisation.
97
3.9
Modelling acids – molecular nature and ionisation.
99
3.13 Strong and weak acids – calculating pH.
101
3.14 Acids as food additives.
105
5.
Esterification
5.7
First-hand investigation: Preparation of an ester by reflux.
131
5.9
Esters – uses in foods and cosmetics.
135
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The Acidic Environment
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Chemical Monitoring and Management Dot Point 1.
The work of chemists
1.1
Researching the work of chemists.
2.
Monitoring in industry – the Haber process
Page
Dot Point
139
2.9
Development of the Haber process and its significance.
141
3.
Chemical analysis
3.1
First-hand investigation: Flame tests.
143
3.2
Monitoring ions in substances we use.
157
3.4
First-hand investigation: Sulfate content of lawn fertiliser.
161
3.5
Analysing reliability of results.
167
3.7
Interpreting data from AAS analysis.
169
Page
4.
Atmospheric chemistry and ozone
4.9
Modelling haloalkanes.
173
4.12 Destruction of atmospheric ozone.
175
4.14 Replacements for CFCs.
177
5.
Monitoring the water supply
5.3
First-hand investigation: Water testing.
179
5.4
Monitoring water for heavy metals and eutrophication.
187
5.5
The local water supply.
193
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Chemical Monitoring and Management
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Industrial Chemistry Dot Point 1.
Resources and replacements
1.1
A natural resource (not a fossil fuel).
2.
Equilibrium and the equilibrium constant
2.1
Page
Dot Point
199
Page
5.
Saponification
5.1
First-hand investigation: Saponification.
235
5.2
Saponification.
239
5.5
First-hand investigation: An emulsion, properties and uses.
241
5.6
First-hand investigation: Soap as an emulsion.
245
First-hand investigation: Modelling an equilibrium reaction.
201
2.2
First-hand investigation: Analysing an equilibrium reaction.
207
2.5
Calculating the equilibrium constant (K). 213
5.11 Environmental impacts of soaps and detergents.
3.
Sulfuric acid
6.
The Solvay process
3.4
Transport and storage of sulfuric acid.
219
6.5
253
3.9
Industrial production of H2SO4 – chemistry and output.
221
First-hand investigation: The Solvay process.
6.6
Calculations involving the Solvay process.
257
6.7
Location of a chemical plant using the Solvay process.
259
3.10 First-hand investigation: Reactions of H2SO4.
225
4.
Sodium hydroxide
4.2
First-hand investigation: Electrolysis of sodium chloride.
229
4.3
Electrolysis of molten and aqueous sodium chloride.
233
249
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Industrial Chemistry
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Shipwrecks, Corrosion and Conservation Dot Point
Page
Dot Point
Page
5.
Corrosion in a sunken ship
5.5
First-hand investigation: Rate of corrosion.
291
5.6
Predicting corrosion rates at depth.
301
267
6.
Corrosion at depth
First-hand investigation: Corrosion of iron and steel.
269
6.1
First-hand investigation: Rate of corrosion and acidity.
2.4
Composition and properties of steel.
273
7.
3.
Electrolytic cells
Salvage, conservation and restoration of artefacts
3.3
First-hand investigation: Rate of electrolysis.
275
7.6
Restoration techniques used in Australian projects.
4.
Corrosion in a marine environment
4.1
History of ship construction – materials used.
279
4.2
First-hand investigation: Corrosion rate of metals and alloys.
281
4.4
First-hand investigation: Prevention of corrosion.
285
4.8
Applications of cathodic protection.
289
1.
The ocean as an electrolyte
1.4
Impact of Galvani, Davy, Faraday and electron transfer reactions.
2.
Ships of metal
2.2
Conditions for rusting.
2.3
263
303
307
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Shipwrecks, Corrosion and Conservation
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DOT POINT *À`ÕVÌÊvÊ >ÌiÀ>Ã
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Production of Materials
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1.3 Identify data, plan and perform a first-hand investigation to compare the reactivities of appropriate alkenes with the corresponding alkanes in bromine water. Background information Alkanes and alkenes are homologous groups of hydrocarbon compounds. Homologous series of hydrocarbons
General formula
Functional group
Example
Alkane
CnH2n+2
–C–C–
Ethane
Alkene
CnH2n
–C=C–
Ethylene (ethene)
Alkanes undergo substitution reactions, e.g. -
light
-
-
-
-
H C - C- H + HF -
-
H C C H + F2 -
-
H F
-
-
H H -
H H
H H
Alkenes undergo addition reactions as they have reactive double bonds, e.g.
-
-
-
H - C - C- H -
C- H + F2
F F -
H- C
-
H
-
H
H H Bromine water is a yellow-brown colour. As it reacts with a hydrocarbon the yellow-brown colour disappears leaving a clear solution. You could also confirm your results by testing the alkane and alkene with acidified potassium permanganate solution (KMnO4). Alkenes will decolourise the purple potassium permanganate but alkanes will not react.
Aim: To compare the reactivity of an alkane and an alkene. Materials Hints: Label any photographed equipment that you used and add any other items used to the list below.
Four test tubes Bromine water (BrOH) Alkane, e.g. cyclohexane (C6H12) Alkene, e.g. cyclohexene (C6H10) Potassium permanganate solution (optional) A fume cupboard
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Production of Materials
Justify the use of these materials. Hints: Cyclohexane and cyclohexene are both colourless liquids. Is this important here? You could also compare the toxicity and volatility of these cyclic hydrocarbons with similar straight-chain hydrocarbons. Why is bromine water used here? Will it show a different reaction rate for an alkane and an alkene? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Hypothesis: Write an hypothesis for this experiment. Hints: From your theoretical knowledge of alkanes and alkenes, predict which will be more reactive and write this as a statement that can be tested. Your prediction should be an educated guess. For example, would you predict that: Cyclohexene will react faster and more vigorously with bromine water than cyclohexane. Or that: Cyclohexane will react faster and more vigorously with bromine water than cyclohexene? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Variables: Identify the following variables in this experiment. Independent variable
Dependent variable
Hint: This is the one thing that you change in your experiment. What is different in your test tubes?
Hint: This is what you measure or observe to see the effect of the one change.
Variables that must be controlled Hint: These are the things that stay the same throughout the experiment.
Risk analysis: Before you carry out any activity you must carry out a risk analysis. Complete the table opposite to indicate any risk involved in using the equipment and chemicals involved in this investigation and explain any necessary precaution for this experiment. The table has been started for you. Hints: This should acknowledge risks to people carrying out the experiment and also to the broader environment. Think about what the risks are in this activity and how you can remove or reduce these risks. You will need to look up the relevant Material Safety Data Sheets. Ask your teacher for these if they are not in the laboratory. Are any of the chemicals you will be using toxic or corrosive? Are there regulations for their safe disposal when the experiment is over?
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Production of Materials
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Dot Point HSC Chemistry Investigations
Chemicals and equipment
Bromine water
Risk
Toxic and corrosive
Describe the precaution
Explain the precaution
Use a fume cupboard, goggles and gloves. Work in a well-ventilated area.
Prevent toxic substances being inhaled, ingested, splashed into the eyes or contacting the skin.
Do not discard into the sink. The used bromine water will be mixed with the alkane and alkene, so can be placed in the organic waste disposal.
Toxic substances would enter environment and could enter the food chain and cause poisoning.
Cyclohexane
Cyclohexene
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Production of Materials
Method: Follow the procedure below and note any modifications you make. 1.
Carry out this procedure in a fume cupboard and wear gloves and safety goggles.
2.
Pour 1 mL cyclohexane into each of 2 test tubes labelled A and B.
3.
Pour 1 mL cyclohexene into each of 2 test tubes labelled C and D.
4.
Cover test tubes A and C so they are in the dark.
5.
Place test tubes B and D in the sunlight.
6.
Add 5 drops bromine water to each test tube.
7.
Tap the side of the test tube gently to mix the contents.
8.
Observe any colour change.
If you are going to confirm your results using potassium permanganate, then write the method below. ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Results: Record your observations. Hints: Results should be tabulated whenever possible. Describe any colour change observed in each test tube and how long it took for the colour to change. Remember that you must always describe results as changing from one colour to another colour, e.g. from yellow to colourless. Do not use the word ‘clear’ when you mean ‘colourless’. ‘Clear’ means you can see through it so coloured solutions can be clear. Did you observe anything else, e.g. did the chemicals separate into layers? Test tube
Initial colour of hydrocarbons
Initial colour of bromine water
Colour after bromine water added to alkane/alkene
Time for change
A B C D
Use a labelled diagram or photographs to illustrate what you observed. Hints: You should always draw diagrams using a pencil and a ruler and label all diagrams fully.
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Write equations in words and symbols. Use structural formulas. Hints: Show what happened when bromine dissolved in water and when the alkane and alkene were added to the bromine water. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Conclusion: Complete the following statements to write a conclusion for this experiment. You must always make sure that your conclusion ‘answers your aim and hypothesis’. The results (support/do not support) the hypothesis. The alkene, cyclohexene, reacted (quickly/slowly) with bromine water, changing colour from ......................................... to .......................................... This happened even in the (light/dark). The alkane, cyclohexane, reacted (quickly/very slowly) with bromine water in the (dark/light) and did not react at all when in the (light/dark). Discussion: Discuss your results under the following subsections. 1.
Account for your results.
Hints: Were they what you expected? Did you notice any layers forming in the test tubes and if so, can you account for this? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
2.
Comment on the accuracy of your results.
Hints: Could the colour change be readily observed? Were the same quantities of chemicals used in each test tube to allow accurate comparison? Was care taken to avoid using excess bromine (which could mask a colour change)? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
3.
Comment on the reliability of your results.
Hint: Was the experiment carried out more than once to check if the results are reliable? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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4.
Comment on the validity of your investigation.
Hints: Did the design of your experiment allow you to test what you set out to test, or could it be improved? Did you have a control? This could be a container of bromine water with no added chemicals – to see if the bromine water would change colour without the addition of cyclohexene. Did you confirm your results by testing the alkane and alkene with acidified potassium permanganate solution (KMnO4)? Are your conclusions valid? Do they accurately reflect the results you obtained. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
5.
Discuss the relevance of this experiment.
Hints: Did performing this experiment help you to understand/remember reactions of hydrocarbon groups? Did your results suggest any further experiments that would be interesting to carry out? To make a polymer, would you use an alkane or alkene as the starting point (raw material)? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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1.7 Analyse information from secondary sources such as computer simulations, molecular model kits or multimedia resources to model the polymerisation process. Background information Monomer – small molecule, e.g. ethylene – many of which join to form a polymer, e.g. polyethylene. Polymer – large molecule made by many monomers joining together, e.g. plastics, PVC, polystyrene, polyester, rubber, starch, cellulose, protein, DNA. Polymerisation – manufacture of a polymer from monomers using heat, pressure and transition metal catalyst. Stages are initiation, propagation and termination. An example is: (where n is a large number)
Describe how you modelled the polymerisation process. Include a diagram or photographs showing the modelling process. If you used a computer simulation, identify its source. Hints: A model shows a representation of reality. It helps you to visualise a structure or process. What did you use to represent the monomers? How did you represent the breaking of the double –C=C– bonds? There are many animations on the internet which model polymerisation. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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Discuss advantages of your model of polymerisation. Hints: Do you understand the process better because you can now visualise it? Did making the model help you to summarise or learn about the process? Can the model be used to make predictions and/or design improvements in the process? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Discuss limitations of your model. Hints: Was your model based on complete information? Could it have been improved if you knew more about the chemicals involved or the process itself? If so, make suggestions. Are there any assumptions behind your model? Is your model a simplification of what is really happening and does this matter? Is your model static or dynamic? Did it include the role of the initiator and catalyst? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Risks and safety assessment: Discuss any risks and how these could be reduced. Hints: Are there any risks involved in this process? If so they are probably minimal. It is acceptable to state that there are no risks or only minimal risks involved in carrying out an activity. If you are using model kits then a risk could be people being bruised if they slip on models dropped onto the floor and thus fall over. Models involving a lot of activity may involve the risks of injury during collisions. Note that the risk is the injury that could result from a collision, not the collision itself. For example, small balls used for modelling are not a risk in themselves, even if they fall on the floor. The risk is that the person may be injured if they slip on balls. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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2.2 Use available evidence to gather and present data from secondary sources and analyse progress in the recent development and use of a named biopolymer. This analysis should name the specific enzyme(s) used or organism used to synthesise the material and an evaluation of the use or potential use of the polymer produced related to its properties.
Background information Biopolymers occur naturally, e.g. starch, cellulose, cotton, proteins, gluten, PHA, polylactic acid. Biopolymers can be made using renewable resources such as plants and micro-organisms, e.g. BiopolR. Biopolymers are renewable, biodegradable and biocompatible. Biopolymers can be modified, e.g. rayon and cellophane are modified cellulose.
Resources and references Use a variety of resources and list the ones you found most useful. Hints: You will need current resources here (within the last couple of years) as this is a developing area of chemistry. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Select one reference that you consulted and decided to ignore. Identify the reference and justify your decision. Hints: When undertaking research it is essential to ensure that all reference material is accurate, reliable and valid. Was the information in this resource inaccurate, unreliable or not valid? Was it just too difficult to understand? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Summary: Use a proforma, such as the ones shown over, to summarise your research findings. You can either write in the information here or type it up on the computer, print it out and add the page(s) here. Hints: Always use your own words. This will increase your understanding and help you to remember the information. Copying information from references without acknowledging the source is called plagiarism and is not acceptable. If you do not understand the information well enough to put it into your own words, then you should get help from your teacher.
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Production of the biopolymer: ...................................................................... Formula of biopolymer Organism or enzyme used to produce this biopolymer
How is it produced?
How has the production process changed over time? Hints: For example, is it now more efficient, does it use new technology such as genetic engineering?
Properties and uses of the biopolymer: ................................................................... Use
Properties that allow it to be used in this way
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Evaluation: Based on the information that you have researched, evaluate the use or potential use of the polymer produced related to its properties. Hints: In an evaluation you should: s
.AMETHEBIOPOLYMERANDSTATEITSFORMULA
s
,ISTITSPROPERTIESANDUSESTHATDEPENDONTHESEPROPERTIES
s
3TATEITSVALUE3AYSOMETHINGLIKE4HEPOLYMERGIVENAME ISEXTREMELYUSEFULVERYUSEFULNOTATALLUSEFULNOTUSEFULNOWBUTWILLBE in the future … Always be specific about what it is useful for. It is useless to just say it is ‘good for people and the environment’, as that is too general.
s
*USTIFYYOUREVALUATIONANDBACKUPYOURCLAIM&OREXAMPLE4HEBIOPOLYMERSTATENAME ISVERYUSEFULINTHEMANUFACTUREOFSTAPLES for use in surgery because it can be produced inexpensively, it is strong enough to hold tissues together, it is biocompatible so it does not cause allergic reactions in people and it eventually biodegrades so it does not have to be surgically removed later.
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Extension question: Show how major advances in the understanding and development of polymers or biopolymers have changed the direction or nature of scientific thinking. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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Notes ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... 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3.3 Process information from secondary sources such as molecular model kits, digital technologies or computer simulations to model the dehydration of ethanol, and the addition of water to ethylene.
Background information Dehydration is a chemical reaction involving the removal of water from a molecule. This is also called condensation. -
-
H H H C - C- OH -
-
-
H2SO4
H
180°C
H
C=C
H H
H
+
O
H
H H
Addition is a chemical reaction that involves the adding of a molecule across a double bond. The addition of water is called hydration. It may also be called hydrolysis because the water molecule is split in the process (to H and OH).
H
+
O
-
H H
dilute acid
-
H
H C - C- OH -
-
C=C
H
-
H
H
H H
H
Dehydration of ethanol 1.
What is meant by dehydration?
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2.
Write an equation for the dehydration of ethanol.
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3.
Describe how you modelled this reaction using diagrams, photographs or videos.
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Addition of water to ethylene 1.
What is meant by an addition reaction?
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2.
Write an equation for the addition of water to ethylene.
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3.
Describe how you modelled this reaction.
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4.
Include diagrams, photographs and/or videos of your model or simulation.
Evaluation: Evaluate your models of dehydration and addition. Hints: Did you successfully illustrate these processes? What difficulties did you encounter? How could you improve this procedure next time? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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Summary: Summarise the advantages and limitations of your models or simulations in the table below: Advantages Hints: Do you understand the process better because you can visualise it?
Limitations Hints: Was your model: s
AVALIDREPRESENTATIONOFTHEPROCESS
Does making the model help you to summarise or learn about the process?
s
BASEDONCOMPLETEINFORMATION
s
BASEDONASSUMPTIONS
Can the model be used to make predictions and/or design improvements in the process?
s
ASIMPLIlCATIONOFWHATISREALLYHAPPENING
Why did you decide to model the reaction in this way?
Could it have been improved if you knew more about the process?
Dehydration of ethanol
Dehydration of ethanol
Addition of water to ethylene
Addition of water to ethylene
Risks and safety assessment: Discuss any risks involved and how these could be reduced. Hints: Are there any risks involved in this process? If so they are probably minimal. It is acceptable to state that there are no risks or only minimal risks involved in carrying out an activity. If you are using model kits then a risk could be people being bruised or injured if they slip on models dropped onto the floor and thus fall over. Models involving a lot of activity may involve the risk of people being injured during collisions. Note that the risk is the injury, not the collision or fall itself. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... Science Press
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3.4 Process information from secondary sources to summarise the processes involved in the industrial production of ethanol from sugar cane. Background information Ethanol (C2H5OH) is an alkanol that can be produced by either the hydration (addition of water) of ethylene or the fermentation of sugars and starches. See also Section 3.12 for fermentation of glucose in the laboratory.
Resources and references Use resources and references to find out about the industrial production of ethanol by the fermentation of sugar cane. Describe the type of reference you used here. Hints: Did you use journals, websites, school textbooks, information from industries or teacher notes and worksheets? If you used the internet did you use key words with AND, OR and NOT when making your searches? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Explain what is meant by the reliability of a resource document. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Identify a strategy you used to determine the validity of your research data. Hints: If a reference provides the data on which their claims are based, and you would draw the same conclusions from this data, then it is a valid reference. Note that many sources do not provide the original data and we assume the information is valid if it is from an expert or reputable source. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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Industrial production of ethanol Use a flow chart to summarise the industrial production of ethanol from sugar cane. Hints: Remember to use arrows (not just lines) to link the steps. And plan it so arrows do not cross over if possible.
During the industrial production of ethanol filtering, fermentation and distillation take place. Using your research, complete the following table to compare these three processes. Filtering
Fermentation
Distillation
Physical or chemical reaction involved? Why is this procedure used?
Outline the procedure
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Discuss technological developments that have improved the industrial production of ethanol. Hints: Include improvements in the processes involved as well as genetic engineering to provide other sources of enzymes, the use of bagasse and raw materials other than sugar cane and uses developed for by-products and waste materials. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... 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Extension activity: Prepare a report for the government informing them of the need for government subsidies to encourage the development of alternative energy sources in Australia. Hints: A report should start with a general statement. This should be followed by a series of paragraphs, each on a different aspect of the issue. The first sentence in each paragraph should summarise what is in that paragraph. Include headings so the reader can see at a glance where the report is ‘going’. You could also include a sentence under each heading that previews what is in the following paragraphs. Technical terms should be used wherever possible. Present tense should be used e.g. ‘Alternative energy sources produce…’ Tables of information can be included if relevant. Include up-to-date information about government subsidies already available. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... 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3.8 Identify data sources, choose resources and perform a first-hand investigation to determine and compare heats of combustion of at least three liquid alkanols per gram and per mole. Background information Combustion is a chemical reaction in which oxygen is used and energy is released. Heat of combustion is the amount of heat released during a combustion reaction. Alkanols are an homologous group of carbon compounds containing the hydroxyl (OH) grouping, e.g. methanol, ethanol, propanol. They have the general formula CnH2n+1OH. This experiment involves the combustion of a measured mass of an alkanol to heat a measured mass of water through a measured temperature rise. It is assumed that the heat released by the combustion reaction will all be absorbed by the water. The heat of combustion can then be calculated using the equation: 'H = –mC'T where:
'H
=
change in energy content (enthalpy change)
m
=
mass of water being heated by the burning alkanol (kg)
C
=
specific heat of the water being heated (4.18 × 103 J kg–1 K–1)
'T
=
change in temperature of water being heated (K)
Note: If the mass used in the equation is in grams, then C must be in J g–1 K–1. The value of C is then 4.18 (not 4.18 × 103).
Aim: To determine and compare the heats of combustion (per gram and per mole) of three liquid alkanols per gram and per mole. Materials: Label the equipment in the photograph which you will use and list any other materials provided by your teacher. Three alkanols, each in its own spirit burner (state names and formulas): .........................................................................................., ......................................................................................................................... and .....................................................................................................................
Safety goggles A container, with 100 mL water, suspended above each spirit burner A thermometer to measure the temperature rise of the water (or temperature probe and data logger) A balance to record the mass of each alkanol before and after burning ..................................................................................................... ..................................................................................................... ..................................................................................................... .....................................................................................................
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Justify the use of these materials and procedures. Hints: Did you need heatproof mats? How did you decide what to use to hold the water? Why is it necessary to weigh the spirit burner both before and after burning the alkanol? Will the alkanols burn readily and safely and release heat to warm the water? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Hypothesis Hints: Make an educated guess about the results – a testable prediction as to which alkanol will release the most or least energy during combustion. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Variables: Identify the following variables in this experiment. Independent variable
Dependent variable
Hint: What was the one thing you changed each time you burned fuel?
Hint: What did you observe or measure to see the effect of changing to another type of fuel?
Variables that must be controlled Hint: What do you have to keep the same each time you burn a fuel?
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Risk analysis: Use the table below to indicate any risk involved in using the equipment and chemicals involved in this investigation and any necessary precaution for this experiment. Hints: Consult the relevant MSDS. Think carefully about the risks involved in burning fuels. Risk
Describe the precaution
Explain the precaution
Alkanols ................................ ................................ ................................
Equipment
Method: Write out the method you will use in procedural text type (‘recipe’ format). Include a labelled diagram (use pencil and ruler as always) or a photograph to illustrate your method. Hints: Put each step on a new line and start each step with a verb. Think about how you will ensure as much heat from the burning alkanol goes into the water as possible. Design your experiment to minimise heat loss to the environment. Remember to stir the water before you measure the temperature rise. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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Results: Complete the following table (or a similar table) to record your results. Add in the names of the alkanols you used. Hints: When tabulating information, always rule lines down between columns and rule across after each section – otherwise it is not a table. Alkanol burning
Alkanol 1
Alkanol 2
Alkanol 3
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.................................................
Initial mass of spirit burner + alkanol (g) Final mass of spirit burner + alkanol (g) Mass of alkanol burnt (initial mass – final mass) Initial temperature of water (before heating) (°C) Final temperature of water (°C)
Rise in water temperature (final – initial) (°C) Volume of water being heated (mL) Mass of water being heated (g)
Any observations you made, e.g. colour of flame, any soot present
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Calculations: Using your results, calculate the heat released by burning the fuel in your experiment and then the heat that would be released if you burnt 1 gram and 1 mole of each fuel. Hints: If you need help, you will find hints and a sample calculation below.
Name of alkanol used Heat released by burning fuel ('H = –mC'T ) Heat released by burning 1 gram of fuel Formula of fuel Molar mass of fuel(g)
Heat released by burning the molar mass of fuel (kJ mol–1) Sample calculation: Ethanol was burned in a spirit burner and used to heat a container of water. The volume of water heated was 100 mL. The mass of the spirit burner and ethanol was 240.0 g before burning and 239.1 g after burning. The temperature of the water rose from 22.0°C to 36.2°C. Hints
Sample calculation
Mass of alkanol burned (g)
Initial mass of spirit burner + alkanol – final mass of spirit burner + alkanol (g)
240.0 – 239.1 = 0.9 g
Initial temperature (°C)
Temperature before heating starts
22.0°C
Final temperature (°C)
Maximum temperature water reaches due to heating
36.2°C
Rise in water temperature (°C)
Final – initial temperature
36.2 – 22.0 = 14.2°C
Volume of water heated (mL)
100 mL
100 mL
Mass of water heated (g)
1 mL water weighs 1 g
100 g
Heat released by burning fuel
Look at the temperature increase.
'H = – 100 × 4.18 × 14.2 = 5935.6 J
Use the equation: 'H = –mC'T where: C = 4.18 J g–1 K–1. Heat released by burning 1 gram of fuel
5935.6 J has been released by burning 0.9 g of fuel
0.9 g of fuel has released 5935.6 J of heat energy by burning.
Formula of fuel
Formula of ethanol is C2H5OH
Molar mass of fuel (g)
Use Periodic Table to find molar mass = 2 × 12.01 + 6 × 1.008 + 16 = 46.068 g
Heat released by burning the molar mass of fuel
1 gram of ethanol will release 6595.1 J heat
(molar heat of combustion)
46.068 g of ethanol will release 6595.1 × 46.068 J = 303691.7.1 J = 303.6917 kJ = 3.04 × 102 kJ The molar heat of combustion of ethanol was found to be: –3.04 × 102 kJ mol–1. Note that this value is well below the value for molar heat of combustion of ethanol given in data books. Can you explain this?
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Graphs: Graph your results to show the heat of combustion per gram and per mole for each fuel. 1.
Graph the heat released by burning 1 gram of fuel for each of the three alkanols.
Hints: Place the type of alkanol (the independent variable) along the horizontal axis and the heat of combustion per gram on the vertical axis. Draw a line of best fit and look for any relationship shown by the graph.
2.
Graph the molar heat of combustion against molar mass of the alkanols.
Hints: Heat of combustion will go on the vertical axis, molar mass on the horizontal axis. Could you use this graph to predict the molar heat of combustion of another fuel, e.g. pentanol? Draw a line of best fit and look for any relationship shown by the graph.
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Equations: Write balanced equations, using words and symbols, to show the combustion of each fuel. Hints: Assume the alkanols underwent complete combustion (products will be carbon dioxide and water). If you noticed a yellow (rather than blue) flame and lots of soot being formed for any of the alkanols, this would indicate incomplete combustion (carbon as one of the products and perhaps carbon monoxide as well). ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Conclusion: Write a conclusion for this experiment. Hints: State the heats of combustion determined experimentally. Remember that heat of combustion should always be shown as a negative value as combustion is an exothermic reaction and heat is released. Compare your experimental values to the accepted values. Compare the experimental heats of combustion for the three fuels. Which fuel releases the most or least heat per gram and per mole burned? Did the graphs show a relationship between molar mass of fuels and molar heat of combustion? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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Discussion 1.
Comment on the accuracy of your results.
Hints: Look up a data book to find the accepted values for heat of combustion of the alkanols you used, e.g.
Alkanol
Heat of combustion (kJ mol–1)
Methanol
–727
Ethanol
–1367
Propan-1-ol
–1367
Propan-2-ol
–2021
Butanol
–2767
Compare these values with the values that you obtained. Are your experimental values accurate? Can you explain the big differences between your values and those in the data book? Did all of the heat released go into heating the water? Did all the fuels burn ‘cleanly’? Did you stir the water being heated so it would heat evenly? Did you measure the highest water temperature recorded? (It may continue to rise after the spirit burner is extinguished.) Was your balance sensitive enough to measure the small change in mass of the fuel? Explain how using graphs contributes to the accuracy of results. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
2.
Does your experiment provide a valid method to determine and compare the heats of combustion of different alkanols?
Hints: Did the design of your experiment allow you to test what you set out to test? Did the water container allow all heat from the burning alkanol to pass through to the water or was heat lost to the environment? Could you prevent any heat loss by improving your experiment? Is this a valid method for determining heats of combustion – does it allow you to obtain accurate and reliable measurement of these? Is this a valid method for comparing heats of combustion – does it allow you to make accurate and reliable comparisons between them? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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3.10
Process information from secondary sources to summarise the use of ethanol as an alternative car fuel, evaluating the success of current usage.
Background information The development of renewable fuels, such as ethanol, from biomass is an interesting area of research. This has become popular with the realisation that petroleum supplies are dwindling and that fuels such as ethanol, although not carbon neutral, do have a lesser impact on the greenhouse effect and global warming as they are produced from plant material.
Resources and references: Use a number of sources to find out about the use of ethanol in car engines. Describe the types of resources you found most useful and identify one website which you felt was presenting a biased view. Hints: Did you use journals, websites, school textbooks, information from industries or teacher notes and worksheets? You will need to be particularly careful that you are using up-to-date information here. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Research report: Write a one-page report on the use of ethanol as an alternative car fuel, evaluating the success of current usage. Hints: You may use point form and tables in your report. Use subheadings and present tense. In your answer you should include the following: s
0ROPERTIESOFETHANOLTHATMAKEITUSEFULASACARFUEL
Does it ignite and burn easily? Include equations. Does it mix well with petrol? Can it be safely stored and transported? Is it renewable? s
5SEOFETHANOLASAFUEL
Find out where ethanol is used as a fuel supplement and how much it is used in different countries. s
!DVANTAGESOFETHANOLASAFUEL
Explain at least three advantages of using ethanol as a fuel rather than other fuels. Remember that to explain you must first state, then describe and then explain how this is an advantage. And an explanation, in chemistry, should include an equation whenever possible. s
$ISADVANTAGESOFETHANOLASAFUEL
Describe and explain at least three disadvantages of using ethanol as a fuel. Use equations. s
%VALUATION
Make a value judgement about the success (or otherwise) of ethanol as a fuel. Is it being suggested as a replacement – why or why not? Is it being used to supplement petrol supplies. Why or why not? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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Extension question 1: A lot has been printed in the mass media about the advantages and disadvantages of using ethanol as a fuel. Assess the accuracy of this information by comparing it with similar information presented in scientific journals. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Extension question 2: Discuss the suggestion that biodiesel made from plants and/or algae may be more useful as a fuel supplement than ethanol. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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3.12
Solve problems, plan and perform a first-hand investigation to carry out the fermentation of glucose and monitor mass changes.
Background information Fermentation of glucose is an anaerobic reaction (no oxygen) in which glucose is converted to ethanol and carbon dioxide in the presence of yeast enzymes such as Saccharomyces cerevisiae. yeast enzymes C6H12O6(aq) ⎯ ⎯⎯⎯→ 2C2H5OH(aq) + 2CO2(g)
A warm environment is needed for the yeast to grow. See Section 3.4 for industrial production of ethanol by fermentation.
Aim: To observe the fermentation of glucose and monitor any changes in mass during this process. Materials: Complete the following list of materials: Safety goggles A container, e.g. flask, for the fermentation process Glucose solution made with water (perhaps 1 g glucose for every 10 mL water) Tubing or cotton wool for the top of the flask (NOT a cork or rubber stopper – pressure, as CO2(g) is produced, could cause an explosion) A way of keeping your flask warm, e.g. an incubator with thermometer A balance to measure the mass of the reacting vessel Yeast – perhaps 1 g yeast per 100 mL Disinfectant Think about how you will determine if fermentation has occurred. Hints: Will you use the sense of smell (to detect alcohol formed), or carry out fractional distillation to isolate any ethanol formed from the mixture in the flask, or use potassium permanganate which changes from purple to colourless when ethanol is present? Will you pass the gas produced through limewater to check that it is carbon dioxide? Your method will determine the other materials you need. List them. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
The photo shows equipment that could be used to carry out this experiment. Hint: If you have a dissolved oxygen (DO) probe you could use it to monitor aerobic conditions during this experiment.
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Justify the use of these materials. Hints: You are using glucose solution and letting it sit around for a while. This would be a good medium to grow microbes, but you do not want to do that for safety reasons. Thus everything must be sterile in this experiment. Sodium metabisulfate solution is a handy steriliser to rinse your flask. Water for solutions can be boiled but must then be cooled before use. Explain why. You need to think of a way to let CO2 gas out of the flask without letting microbes in. Why do you have to set up an identical set of equipment without any yeast in it (the control)? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Hypothesis: Write an hypothesis. This must be a statement that can be tested – your prediction of the most likely results. Hints: Mass stays the same during any chemical reaction (Law of Conservation of Mass). Of course you will only observe this if you do not let any reactants or products escape from the reaction vessel. Look at the equation for fermentation to see what the products are, then think about how you are performing this experiment and decide if you expect the mass to increase or decrease or stay the same during this experiment. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Variables Explain why the presence or absence of yeast is the independent variable. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Explain why the mass of the flask and contents is the dependent variable. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Identify any variables that must be controlled – in what ways must the experimental and control flasks be identical? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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Risk analysis: Evaluate any risk involved in carrying out this investigation and explain any necessary precautions. As you are using glucose and a yeast culture you should also consider any biological risks. Hint: Do not forget to describe the safe disposal of the mixture after the experiment. Include biological risks. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Method: Write out the method you will use in procedural text type. Put each step on a new line and start each step with a verb. Include a diagram or photographs to illustrate your method. Hints: Think about how to remove oxygen (fermentation is an anaerobic process), provide a sterile environment, maintain the reaction flask at constant temperature, set up a control (an identical flask without yeast), identify any gas produced by the reaction, and show that you have actually produced ethanol in the flask. Also, how long will you need to observe your experiment and how often will you need to weigh the reaction flask and contents? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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Results: Draw up a table such as the one below to record your results. Fill in vertical lines as needed. Hints: When tabulating information, always rule lines down between columns and across after each section – otherwise it is not a table.
Date and time Mass of flask and contents (g) Other observations
Equations Write an equation (words and symbols) for the fermentation of glucose (C6H12O6). Hints: You only have one reactant for this reaction. Oxygen is NOT used in fermentation. Indicate above the arrow that enzymes are needed for the reaction to proceed. ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Write an equation to show the effect of carbon dioxide on limewater. Hint: Limewater is calcium hydroxide solution (Ca(OH)2). ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Conclusion: Write a conclusion for this experiment. Hints: What did you find out? Did the mass change as predicted in your hypothesis? When you write a conclusion always refer back to your aim and hypothesis. Your conclusion should ‘answer these’. For example, you could start with, ‘My results support (or do not support) my hypothesis.’ ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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Calculations Calculate the volume of carbon dioxide released during your experiment. The table below gives a sample calculation (on the left) for the volume of carbon dioxide released during a fermentation reaction. Write in YOUR results and calculations on the right-hand side. Sample calculation
Mass ‘lost’ during fermentation
Your calculation
5.3 g
Assume all the mass loss is due to the release of carbon dioxide gas (no evaporation or spillage) Molar mass of carbon dioxide (Use Periodic Table)
CO2 = 12.01 + 2 × 16 = 44.01 g
Number of moles of CO2 gas released during experiment
Mass/molar mass = 5.3/44.01 = 0.1204271 mol
Assume temperature is 25°C and atmospheric pressure is 100 kPa Volume occupied by 1 mole of any gas (including CO2) at 25°C (298.15 K) and 100 kPa = 24.79 L Volume of CO2(g) released
1 mol releases 24.79 L 0.1204271 mol releases 24.79 × 0.1204271 L = 2.9853897 L or allowing for significant figures: 3.0 L
Discussion Comment on the accuracy of your experimental results. Hints: It is assumed that you can manipulate and use apparatus correctly without spillages and can measure quantities properly. The sorts of issues you should discuss here are things like the difficulty of identifying the presence of ethanol or removing ethanol from the mixture left after the experiment. (Ethanol is difficult to remove as it bonds with water present in the flask.) Did you manage to produce much ethanol? Does the ethanol produced affect the yeast cells? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Comment on the reliability of your results. Hints: Did you have time to repeat the experiment? Did different groups in the class obtain the same results? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Comment on the validity of your experimental method. Hints: Did the design of your experiment allow you to test what you set out to test? Was all of any mass change due to loss of carbon dioxide gas or could any water evaporate? Did you use a control? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... Science Press
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4.1 Perform a first-hand investigation to identify the conditions under which a galvanic cell is produced. Background information Galvanic cell – an arrangement which allows a spontaneous redox reaction to take place in such a way that electricity is produced. A galvanic cell can be made with: s
TWOHALF CELLSEACHCONTAININGANELECTRODEINELECTROLYTESOLUTION
s
AWIRECONNECTINGTHETWOELECTRODES
s
ASALTBRIDGECONNECTINGTHETWOELECTROLYTES
Aim: To identify the conditions under which a galvanic cell is produced. Materials: The photo shows equipment you might use to carry out this experiment. Label any of this equipment that you used.
List the materials provided by your teacher. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Justify your use of these materials. Hints: Do you have two different metals, each in an electrolyte solution? Are the metals connected so any electricity produced can flow? Do you have equipment that can detect any current flowing? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... Science Press
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Risk analysis: Carry out a risk analysis for this investigation before you commence. Hints: Use MSDS sheets to check any precautions needed for each of the chemicals you are using. Chemicals and equipment
Risk
Describe the precaution
Explain the precaution
Method: Write out the method you will use in procedural text type. Put each step on a new line and start with a verb. Include a labelled diagram and/or photographs to illustrate your method. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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Results: Describe any observations made during your investigation. Hints: Look for a voltage, any gas, any deposits, any corrosion of electrodes. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Conclusion: Write a conclusion for this experiment. Hints: Did you produce any electricity using two different metals in an electrolyte? Remember to ‘answer the aim’ – identify all the conditions necessary to form a galvanic cell. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Discussion of results Hints: Could you improve on this experiment? Do the results suggest further investigation? Comment on the accuracy, reliability and validity of this investigation. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... 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4.2 Perform a first-hand investigation and gather first-hand information to measure the difference in potential of different combinations of metals in an electrolyte solution. Background information When different metals are placed in an electrolyte a potential difference exists between the metals. This potential difference can be measured. If the metals are joined by a wire an electric current may flow between them.
Aim: To measure the difference in potential of different combinations of metals in an electrolyte solution. Materials: The photos show some equipment you might use to carry out this experiment. Label them. List the materials provided by your teacher. These will probably include: Safety goggles Beakers A variety of clean metal electrodes – A variety of ................................................................... mol L–1 salt solutions (state names and formulas): ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... .....................................................................................................................
Alligator clips Electrical wires A strip of filter paper for a salt bridge Solution, e.g. potassium nitrate (KNO3) to soak the salt bridge Voltmeter, galvanometer or multimeter to measure any potential difference ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... .....................................................................................................................
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Hypothesis: Write an hypothesis for your experiment. Hints: This must be a statement which can be tested experimentally. Do not write it as a question. Can you predict which combinations of metals will produce the greatest or least potential difference? The redox table at the back of this book might help you. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Risk analysis: Check MSDS sheets for any risks and precautions needed for the chemicals you are using. Chemicals and equipment
Risk
Describe the precaution
Explain the precaution
Method: Complete the method below. Include a labelled diagram or photograph to illustrate the method you used. 1.
Check that your electrodes are clean.
2.
Place the ................................................................... electrode in a solution of ................................................................... in a beaker so the electrode is ................................................................... in solution.
3.
Place the ................................................................... electrode in a solution of ................................................................... in a beaker so the electrode is ................................................................... in solution.
4.
Place the beakers containing the electrolytes close together.
5.
Make a salt bridge (e.g. by soaking a strip of filter paper in potassium nitrate). Science Press
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6.
Keep the salt bridge moist throughout the experiment.
7.
Connect wires (use alligator clips if necessary) to each electrode.
8.
Connect these wires to a galvanometer, ammeter or multimeter.
Note: If the needle of the voltmeter or galvanometer moves in a backward direction you must immediately disconnect the meter and reverse the wires before reconnecting. 9.
Read the voltage produced and record this value in a table.
10.
Repeat your reading. Photograph the experiment.
11.
Dismantle your equipment, dispose of solutions appropriately and clean thoroughly (especially electrodes which may be reused).
12.
Repeat steps 1 to 11 for each combination of electrodes and electrolytes provided.
Results: Record any observations in a table such as the one below. Hints: Did you produce and measure a voltage? Look for any corrosion of electrodes, production of gas, or the formation of any deposits.
Metal electrodes
Electrolytes (salt solutions)
Magnesium
Magnesium sulfate
Copper
Copper sulfate
Potential measured (volts)
Other observations
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Conclusion: Write a conclusion for this experiment. Hints: Was there a potential difference when two different metals were placed in an electrolyte? Did the potential difference differ for different pairs of metals? Was there any trend in results? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Discussion of results 1.
Explain any trend in the results that you observed.
Hint: Was the potential difference between the pairs of metals related to their reactivity? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
2.
Comment on the accuracy of your investigation.
Hints: Is this a qualitative or quantitative experiment? Did you allow for any zero error for the voltmeter or galvanometer you used? Did you clean the electrodes before you began? Were all the metal electrodes immersed to the same level? Are you sure there was no contamination of electrolyte solutions from previously used electrodes? Was the salt bridge kept moist throughout the experiment? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
3.
Assess the method described above, especially in relation to the reliability and validity of this investigation.
Hints: Did the description of the method provide enough information to ensure that anyone reading it could follow exactly the same method as you used? Does the design of your experiment allow you to test what you set out to test? Were instructions sufficiently detailed to allow for the control of all relevant variables? Can you explain the reason for each step in the method, e.g. why the salt bridge must be kept moist. How could you improve on the instructions for this experiment? Compare the photographs you took for each pair of metals. Was the method identical for each pair? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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4.9 Solve problems and analyse information to calculate the potential E requirement of named electrochemical processes using tables of standard potentials and half equations. Background information A redox table is a list of standard reduction potentials (E ). A standard reduction potential is the relative tendency of a substance to gain one or more electrons when compared with the standard hydrogen half-cell. Reduction potentials are measured under standard conditions. This means a temperature of 25°C, a pressure of 100 kPa and an electrolyte concentration of 1 mol L–1. The standard reduction potentials (E ) for a galvanic cell can be calculated as follows: s
WRITETWOHALFEQUATIONS
s
LOOKUPTHERELEVANTSTANDARDPOTENTIALSFOREACHHALFEQUATIONINTHEREDOXTABLE
s
CHANGETHESIGNFORTHEOXIDATIONHALFREACTION
s
ADDTHETWOHALFEQUATIONSANDSTANDARDPOTENTIALS
Note: If you find this topic difficult, you might find it helpful to look at the book by M Schell and M Hogan titled, Surfing: Production of Materials, Sections 17 to 21.
4.9.1
(a)
Write a half equation to show the reduction of copper ions (Cu2+) to copper metal.
.........................................................................................................................................................................................................................................................
(b)
Use the redox table at the back of the book to find the voltage needed for this reduction to take place.
.........................................................................................................................................................................................................................................................
(c)
Change this equation to show the oxidation of copper metal to form Cu2+ ions.
.........................................................................................................................................................................................................................................................
(d)
State the voltage generated by this oxidation reaction.
.........................................................................................................................................................................................................................................................
4.9.2
(a)
Write a half equation to show the reduction of magnesium ions (Mg2+) to magnesium metal.
.........................................................................................................................................................................................................................................................
(b)
Use the redox table at the back of the book to find the voltage needed for this reduction to take place.
.........................................................................................................................................................................................................................................................
(c)
Change this equation to show the oxidation of magnesium metal to form Mg2+ ions.
.........................................................................................................................................................................................................................................................
(d)
State the voltage generated by this oxidation reaction.
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4.9.3
The reduction of copper ions and magnesium ions, in separate, appropriate galvanic cells, can generate a potential difference as shown by the following equations and standard potentials: Mg2+ + 2e– ĺ Mg (s)
–2.36 V
Cu2+ + 2e– ĺ Cu(s)
+0.34 V
Which ions are more easily reduced? Justify your answer. .........................................................................................................................................................................................................................................................
4.9.4
In appropriate galvanic cells, under standard conditions, the oxidation of copper metal and magnesium metal will have half-cell potentials as shown: Cu(s) U Cu2+ + 2e–
–0.34 V
Mg(s) U Mg2+(aq) + 2e–
+2.36 V
(a)
Which metal is more active?
.........................................................................................................................................................................................................................................................
(b)
Which metal is more likely to be oxidised if the metals copper and magnesium are placed together?
.........................................................................................................................................................................................................................................................
4.9.5
A galvanic cell is set up with magnesium in magnesium ions connected to copper in copper ions. (a)
Write half equations for the oxidation and reduction reactions that will occur.
......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
(b)
Add these two half equations to obtain an equation for the cell and calculate the voltage by this cell using standard conditions.
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4.9.6
The following diagram shows a galvanic cell. e−
V
e−
+
-
Electrode B
Electrode A
Salt bridge
(a)
Which electrode is the anode?
.........................................................................................................................................................................................................................................................
(b)
Which electrode is made of the more active metal?
.........................................................................................................................................................................................................................................................
(c)
At which electrode does oxidation occur?
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(d)
If electrode A is copper, in a solution of copper(II) nitrate and electrode B is iron, in a solution of iron nitrate, write two half equations to show oxidation and reduction in this cell. Add these to calculate the voltage produced by this cell under standard conditions.
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4.9.7
In an electrochemical cell the following overall cell reaction occurs: 2Ag+(aq) + Cu(s) ĺ Cu2+ (aq) + 2Ag(s) (a)
Write the two half equations for this reaction and identify which is oxidation.
......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
(b)
Calculate the cell voltage if standard conditions apply.
.........................................................................................................................................................................................................................................................
(c)
Draw and label this cell.
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4.10 Gather and present information on the structure and chemistry of a dry cell or lead-acid cell and evaluate it in comparison to one of the following: button cell, fuel cell, vanadium redox cell, lithium cell, liquid junction photovoltaic device (e.g. the Gratzel cell) in terms of: chemistry, cost and practicality, impact on society, and environmental impact.
Identify the types of cells illustrated above. Resources and references: List the references you found most useful here. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Discuss the validity of your information sources. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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Summary: Use the proforma below to summarise the information you obtain. Alternatively you could use a PowerPoint presentation. The dry cell (Leclanche cell) OR lead-acid cell
Other cell (See list on previous page)
Diagram
Anode (oxidation) Include an equation Cathode (Reduction) Include an equation Electrolyte
Uses of cells
Advantages
Disadvantages
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The dry cell (Leclanche cell) OR lead-acid cell
Other cell (See list on previous page)
Relative cost
Practicality
Impact on environment
Impact on society
Extension question: Batteries convert chemical energy to electrical energy. Discuss possible future directions of energy conversion research. Hints: A discussion should include points for and against. Use subheadings. Use point note form. You will not be penalised for opinions that differ from those of the examiner as long as you have supported your opinion with facts. You should start with a general statement about the need of society for increasing amounts of energy, particularly electrical energy, the decreasing supplies of traditional energy sources and the need for energy conversions to meet peoples’ perceived needs. Explain the need for smaller, longer lasting batteries that recharge quickly and for efficient batteries to store energy produced by sources such as solar cells Identify a number of ways electrical energy can be obtained from other types of energy and discuss the advantages and disadvantages of each. This could be covered in a table. Consider possible future directions of energy conversions. Are we likely to continue to obtain electrical energy from chemical energy (burning coal and batteries) or will we turn to other sources, e.g. wind, solar, tides, biofuels? ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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5.2 Process information from secondary sources to describe recent discoveries of elements. Resources and references: Use a number of sources to find out about recent discoveries of elements and list the references you found most useful here. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
Summary Use the following proforma to summarise research information about recently discovered elements. Alternatively you could use a PowerPoint presentation to report your research. Name and symbol of recently discovered elements
When discovered (year)
How it is produced
Equation for production
Discuss the accuracy, reliability and validity of this information. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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5.8 Use available evidence to analyse benefits and problems associated with the use of radioactive isotopes in identified industries and medicine. 5.8.1
The following radioisotopes are used in medicine: Radioisotope
Radiation emitted
Half-life
Uses
Iodine-131
Beta, gamma
8 days
Treating cancer of the thyroid gland.
Technetium-99m
Gamma
6 hours
Diagnosis of conditions of internal organs, e.g. brain, lungs, heart and blood flow.
Cobalt-60
Beta, gamma
5.3 years
Gamma irradiation of cancers.
Analyse benefits and problems likely to be associated with the use of these isotopes in medicine. Hints: When given information in a question, always quote it in your answer. Look for things that these isotopes have in common, e.g. relatively short half-life, no ionising alpha radiation emitted and explain why these properties are an advantage in medicine. Also look at what is unique about each, e.g. why is iodine-131 used specifically for thyroid conditions whereas technetium-99m has broader uses? You can also bring in other information that you have researched, e.g. safety of workers, transport and security. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... 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5.8.2
The following table summarises information about some radioisotopes used in industries: Radioisotope
Radiation emitted
Half-life
Uses
Caesium-137
Beta, gamma
30 years
Testing thickness of metals.
Americium-241
Alpha, low-energy gamma
432 years
Smoke alarms.
Gold-198
Beta, gamma
2.7 days
Tracing movement of sand in rivers and oceans and sewage through waterways.
Analyse benefits and problems likely to be associated with the use of these isotopes in industry. Hints: Remember to quote figures from the table in your answer. What are the advantages of each of these radioisotopes? What are the problems – look at the types of radiation emitted and half-lives. ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................... .........................................................................................................................................................................................................................................................
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5.8.3
5.8.4
Complete each of the following equations involving radioactive isotopes.
M →
(a)
99 42
99 43
(b)
3 1
(c)
...................................................................................
(d)
226 88
Tc +
...................................................................................
H → 32 He + ...................................................................................
Ra →
222 86
→
234 90
Th + 42He
Rn + ...................................................................................
Read the following information and then answer the questions below. Thallium-201 is a radioactive isotope which is produced in a cyclotron. A cyclotron uses electromagnetic forces to accelerate charged particles. Thallium-201 has been used for 30 years in medical diagnosis of heart problems as it provides good images of heart muscle, showing which muscles are working efficiently and receiving a good supply of blood. Thus it can be used to assess a patient’s risk of heart attack and help doctors to decide the most appropriate treatment. Thallium-201 emits gamma radiation and has a half-life of 73 hours It can enter cells quickly because it has ions which are similar to potassium ions so it can behave like potassium biologically. A solution of thallium-201 is injected into the blood. It travels to areas of the heart which have adequate blood supply and collects in heart muscle cells there. The patient is scanned using a sophisticated camera that photographs the low-energy gamma rays emitted and produces a three-dimensional image of the heart. The scan will show which areas of the heart have received blood and which have not. Differences in scan results, when a person is at rest and after exercise, will help doctors to diagnose heart problems. Iodine-123 is also produced in a cyclotron. This radioisotope is used to diagnose thyroid diseases. Iodine-123 has a halflife of 13 hours and produces low-energy gamma radiation which produces good images. Doses of iodine-123 are injected into patients to find out if thyroid cancers have spread to other organs such as the lungs, chest and abdomen. Thyroid tissue absorbs iodine, so any cancers which originated in the thyroid glands will absorb this iodine-123 and show up on gamma scans. Iodine-131 is produced in a nuclear reactor. This radioisotope has a half-life of 8 days. It produces a higher dose of radiation so provides a good way of treating thyroid cancers. The patient is given a drink containing the radioactive iodine-131 and must remain in isolation in hospital for a few days until their body level of radioactivity has decreased to a safe level.
(a)
Outline three advantages of the use of thallium-201 in the diagnosis of heart disease.
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(b)
Distinguish between the use of iodine-123 and iodine-131 in patients with thyroid cancer.
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DOT POINT ««i`Ý
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Appendix
Answers Production of Materials 4.9.1
(a)
Cu2+(aq) + 2e–ĺCu(s)
+0.34 V
Hint: See redox table at back of book for voltages.
4.9.2
(b)
+0.34 V
(c)
Cu(s)ĺCu2+(aq) + 2e–
(d)
–0.34 V
(a)
Mg2+(aq) + 2e– ĺ Mg(s)
(b)
–2.36 V
(c)
Mg(s) ĺ Mg2+(aq) + 2e–
(d)
+2.36 V
–0.34 V
–2.36 V
+2.36 V
4.9.3
Copper ions – the one with the higher E value.
4.9.4
(a)
magnesium
(b)
magnesium
(a)
Mg(s) ĺ Mg2+(aq) + 2e–
+2.36 V
Cu (aq) + 2e ĺ Cu(s)
+0.34 V
4.9.5
2+
(b)
4.9.6
4.9.7
–
Mg(s) ĺ Mg2+(aq) + 2e–
+2.36 V
Cu2+(aq) + 2e– ĺ Cu(s)
+0.34 V
Mg(s) + Cu2+(aq) ĺ Mg2+(aq) + Cu(s)
+2.70 V
(a)
Electrode A
(b)
Electrode A
(c)
Electrode A
(d)
Cu(s) ĺCu2+(aq) + 2e–
–0.34 V
Fe2+(aq) + 2e– ĺ Fe(s)
–0.44 V
(a)
(b) (c)
Cu(s) + Fe2+(aq) ĺ Cu2+(aq) + Fe(s)
–0.77 V
Cu(s)ĺCu2+(aq) + 2e–
–0.34 V Oxidation
Ag+(aq) + e–ĺAg(s)
+0.80 V
(–0.34 ) + (+0.80) = 0.46 volts Salt bridge
Copper anode
V e-
Negative ions Positive ions
Cu2+ ions
5.8.3
(a)
0 1
(b)
0 1
(c)
238 92
(d)
4 2
Silver cathode
Ag+ ions
e e U
He
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