Production of Materials

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1. Fossil fuels provide both energy and raw materials such as ethylene, for the production of other substances x Construct word and balanced equations of chemical reactions as they are encountered

eat o carbon dioxide  water methane  oxygen h eat CH 4(g)  2O 2(g) h o CO 2(g)  2H 2 O (g) eat CH 4(g)  O 2(g) h o C (s)  2H 2 O (g) nergy o glucose  oxygen carbon dioxide  water e nergy 6CO 2(g)  6H 2 O (l) e o C 5 H 12 O 6(aq)  6H 2 O (l)

ethane m o ethylene  hydrogen C 2 H 6(g) m o C 2 H 4(g)  H 2(g) ddditon ethene  chlorine a o1,2  dichloroethane ddition o C 2 H 4 Cl 2(g) C 2 H 4(g)  Cl 2(g) a ddition hexene  bromine a o1,2  dibromohexane ddition C 6 H 12(l)  Br2(g) a o C 6 H 12 Br2(l) ddition ethane  Bromine a o1  bromoethane  hydrogen bromide ddition C 2 H 4(g)  Br2(g) a o C 2 H 5 Br(g)  HBr(g) atalyst o polyethylene ethylene c n

atalyst (C 2 H 4 ) c o n (...  C 2 H 4  ...)

nzyme o glucose  fructose sucrose  water e nzyme o C 6 H12 O 6(aq)  C 6 H 12 O 6(aq) C12 H 22 O11(aq)  H 2 O (l) e nzyme glucose e o ethanol  carbon dioxide nzyme o 2C 2 H 5 OH (l)  2CO 2(g) C 6 H 12 O 6(aq) e eat ethanol  oxygen h o water  carbon dioxide eat C 6 H 5 OH (l)  3O 2(g) h o 3H 2 O (l)  2CO 2(g)

1

x Identify the industrial source of ethylene from the cracking of the fractions from the refining of petroleum

Petroleum consists of crude oil and natural gas. Crude oil is a complex mixture of long, straight branched and cyclic hydrocarbons while natural gas is composed of methane and ethane. Ethylene is obtained from crude oil. Petroleum is separated into crude oil and natural gas, then smaller hydrocarbons by fractional distillation. Fractional distillation separates the ‘fractions’ based on their boiling points. The refinery gas fraction (C1 to C4) has the lowest boiling point ( C70- residue for bitumen & roofing

2

Ethylene is manufactured from LPG, naphtha or gas by the process of cracking. Cracking breaks down long chain hydrocarbons into smaller chain alkenes and alkanes. There are two types of cracking: thermic and catalytic. Thermic cracking involves the use of metal coils called pyrolysis coils. The coils are heated to high temperatures under high pressures (7000kPa) and the presence of steam. Ethylene and hydrogen gas can be produced by the cracking of ethane: eat C 2 H 6(g) h o C 2 H 4(g)  H 2(g)

Catalytic cracking involves the use of a zeolite (catalyst, used inside a tall column called a cat cracker. Use of a catalyst reduces energy savings as less heat (and no oxygen) is required. The inside of the cat cracker is porous structure that maximises surface area. Long-chain hydrocarbons are pre-heated and sprayed into the base where the cracking process occurs. x

Identify that ethylene, because of the high reactivity of its double bond, is readily transformed into many useful products

Ethylene is highly reactive due to its double bond. Ethylene readily undergoes addition reactions where a double bond is broken and other atoms ‘added in’ at the double bond. Addition reactions include: - Addition of hydrogen (hydrogenation) turns alkenes into alkanes - Addition of halogens to form haloalkanes - Addition of water (using concentrated H+ catalyst) to form ethanol - Polymerisation of ethylene to form polyethylene Addition reactions with ethylene: Reactant Addition Reaction H2 C2H 4  H 2 o C2H6 Br2 C 2 H 4  Br2 o C 2 H 4 Br2 H2O C 2 H 4  H 2 O o C 2 H 4 OH HBr C 2 H 4  HBr o C 2 H 4 OH Useful products using ethylene as feedstock include: Chemical Reaction Product Formed Polymerisation of LDPE ethylene/haloethenes HDPE PVA (Polyvinyl acetate) PVOH (Polyvinyl alcohol) PVC (Polyvinyl chloride) oxidation 1,2-diethandiol Acetic acid halogenation Chloroethane; bromoethane hydration ethanol

Product Ethane 1,2-dibromoethane ethanol bromoethane

Uses Cable coating; film and sheeting Water piping; appliances Adhesives Adhesives; film Water piping; roofing Antifreeze Solvent, antifreeze Solvent; refrigerant Cosmetics, disinfectants; solvents

3

x Identify data, plan and perform a first-hand investigation to compare the

reactivities of appropriate alkenes with the corresponding alkanes in bromine water

Experiment: Comparing the reactivity of alkanes and alkenes Aim: To compare the chemical reactivity of an unknown alkane and alkene with bromine water and potassium permanganate. Equipment: 4 test tubes Safety glasses Br2(aq)

test tube rack unknown alkane and alkene (A and B) 0.01 mol/L KMnO4(aq) acidified with H2SO4(aq)

Procedure: 1/ Place 25ml (or a fixed amount) of A into 2 test tubes. Repeat with B for the two remaining test tubes. Place test tubes in test tube rack. 2/

Put three drops of KMnO4 solution into one sample of A and B. Observe and record results.

3/

Put three drops of bromine water into one sample of A and B. Place samples in UV light (sunlight). Observe and record results.

Safety: Wear safety glasses at all times. Avoid inhaling any vapours from A and B. Bromine water is poisonous and should be handled with care, as should the acidified potassium permanganate solution. If contact with skin occurs wash immediately with plenty of water. Results: Sample Reaction with Br2(aq) Br2(aq) decolourises No reaction.

A B

Reaction with acidified KmnO4(aq) KmnO4(aq) decolourises No reaction.

Hydrocarbon (alkane/alkene) alkene alkane

Hexene  Bromine water  o1,2  dibromohexane C 6 H 12(aq)  Br2(aq)  o C 6 H 12 Br2(l)

H

H

H

H

H

H

C

C

C C

C

C

H

H

H

H

H

H C H

+ Br2

H

H

H

H

H

Br

Br

C

C

C C

C

C

C

H

H

H

H

H

H

When bromine is dissolved in an organic solvent (water, in this case), the final addition product is always a dibromoalkane (C2NBr2). Conclusion: Alkenes are more reactive than their corresponding alkanes.

4

H

x Identify that ethylene serves as a monomer from which polymers are made n

atalyst CH 2 ) c o n (...  CH 2 CH 2  ...) where n

(CH 2

500  50000

In the presence of a catalyst, the monomer ethene polymerises to form polyethylene. Various types of polyethenes with branched or linear chains can be produced by highor low-pressure methods.

x Analyse information from secondary sources such as computer simulations, molecular model kits or multimedia resources to model the polymerisation process

Polyethylene: H

H C

n

polymerisation

C



H

H

H

H

H

H

H

H

C

C

C C

C

C

C

H

H

H

H

H

H



Polyvinyl chloride: H

H C

n

polymerisation

C



Cl

H

H

H

H

Cl

H

H

C

C

C C

C

C

C

H

Cl

H

H

H

Cl

H

H

H

H

H

H

C

C

C C

C

C

C



Polystyrene: H

H C

n

H

C

polymerisation



H

H

H

5



x Outline the steps in the production of polyethylene as an example of a commercially and industrially important polymer

Steps in polyethylene production: 1)

Ethylene is compressed, cooled and pumped under high pressure onto a fluidised bed reactor containing polyethylene powder

2)

Ethylene gas is pumped up below the bed, making it behave like a liquid.

3)

Initiation- For HDPE, a transition metal (Zeigler-Natta) catalyst initiates the reaction under low pressures. For LDPE a peroxide containing an O-O bond is added. The peroxide breaks ethylene’s double bond, forming ethylene free radicals which are highly reactive. LDPE forms under high pressures.

4)

Propagation- monomers join and Polyethylene forms at the interface of the catalyst. The length of the polymer chain will depend on the reaction time.

5)

When complete chains form, the process is terminated. Polyethylene is cooled and separated from ethylene.

6)

The polyethylene is mixed with additives such as plasticisers that alter the properties (e.g. flexibility, softness, reduce friction, colour). It is extruded, moulded or pelletised, dried and packaged.

Low cooking pressures form hard HDPE, consisting of tightly packed, linear chains. Dispersion forces are strong, so it is rigid, strong and opaque with a crystalline structure.

High cooking pressures temperatures form softer LDPE, consisting loosely arranged branched chains. The side chains inhibit efficient packing of the chains, so dispersion forces are weaker and the chains slide along eachother easily. This makes LDPE soft, flexible and transparent.

6

x Identify polyethylene as an addition polymer and explain the meaning of this term

Polyethylene is produced in an addition reaction called polymerisation in which monomers of ethylene join together to form long molecules i.e. polymers. During this process, ethylene’s double bond is broken via heat, pressure and a catalyst. NO other products except the polymer are formed.

x Identify the following as commercially significant monomers:

-vinyl chloride -styrene by both their systematic and common names x

Describe the uses of the polymers made from the above monomers in terms of their properties

Monomers

Common Name Ethylene

Vinyl chloride Styrene

Systemic Name ethene

Name

Polymers

Properties

LD polyethylene

-Low density -Soft -Flexible -transparent HD polyethylene -High density -Durable -rigid chloroethene polyvinylchloride -Fire retardant -Weather resistant ethenylbenzene polystyrene -Insulator -Very light -Mouldable -Transparent -forms foam when gas is added

Uses -glad wrap -disposable food bags -Water piping -Hula hoops -Bottle caps -Roofing -Tiling -Water pipes -Plastic toys -disposable cups -Plastic cutlery -housing insulation

How does the structure of polystyrene relate to its use? Polystyrene is chemically unreactive, rigid and strong which lends it well to use in electronics, appliances and containers for food, chemicals and solvents. This chemical stability is due to strong intramolecular forces. Polystyrene is a fully saturated molecule, containing only single bonds. Polystyrene is also highly flexible due to weak Van Der Waals forces between the polymer chains. This flexibility means it is used for plastic toys, as well as food packaging.

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The combination of the strong intramolecular forces and weak intermolecular forces means the polymer chains slide along eachother, making polystyrene flexible and stretchable. This ability to be easily deformed means it is readily softened with the addition of heat. Because of this, polystyrene can be extruded into CD cases, licence plates and other objects that require a fairly strong, rigid plastic and manufactured into foam for as housing insulation and packaging. The weak intermolecular forces also allow it to be combined with other polymers and compounds to produce copolymers with enhanced properties e.g. high-impact polystyrene for use in signs, appliances, electrical goods and furniture. Plasticisers are additives that increase the flexibility of the polymer. Plasticised polystyrene is used in many medical products, flexible roof tiles and rainwear.

2. Some scientists research the extraction of materials from biomass to reduce our dependence on fossil fuels x Discuss the need for alternative sources of the compounds presently obtained from the petrochemical industry

Petrochemicals are derived from compounds in petroleum or natural gas. Australia’s reserves are limited- petroleum reserves will last bout 10 years and natural gas, 100 years. These fuels take millions of years to accumulate. Over 95% of fossil fuels are used as fuel for transport and less than 5% is used for plastics. Even less than this is recycled. If energy and material needs are to be met in the future, alternative sources will be required as fossil fuels are used up.

x Explain what is meant by a condensation polymer Condensation polymers form when two monomers bond with the elimination of a small molecule such as water between functional groups as the polymer chain forms. Each monomer has AT LEAST two functional groups (one at either end of the molecule) that condenses out the small molecule. Common function groups include alkanol (OH), carboxylic acid (COOH) and amine (NH2).

8

x

Describe the reaction involved when a condensation polymer is formed

Polyesters are condensation polymers formed when a diol or glycol monomer (two OH functional groups) bonds with a dialkanoic acid monomer (two OH functional groups AND an COOH group). The polymer formed is known as a dimer molecule. The -OH from the acid and the H from the –OH (alcohol) functional group combine to form water. The bond that forms between the monomers is called an ester linkage (-OCO-). Polyethylene terephthalate (PET) is an example of a polyester: H HO

n

H

H

+

OH

C

O

O

n

H

C

C

OH

OH Terephthalic acid

Ethylene glycol

The OH from the acid and the H from the glycol form the water molecule. Ester linkage in red

… n

O

H

H

C

C

H

H

O

O

O

C

C

PET “dimer” molecule

O



+

n

H

H Water

Polyesters are used to make plastic bottles, LCD’s, film insulation, tarpaulins and wiring insulation. Polyamides and polypeptides (aka proteins) are condensation polymers formed when a diamine (two NH2 functional groups) monomer (two OH functional groups) bonds with a dialkanoic acid monomer (two OH functional groups AND an COOH group). The bond that forms between the monomers is called a peptide bond (-CONH-). Polyamides are synthetics such as nylon and are commonly used in textiles, automotives, carpet and sportswear due to their extreme durability and strength. Polypeptides or proteins form from amino acid monomers and are naturally occurring e.g. wool, silk.

9

Nylon 6,6 is an example of a polyamide: H N

n

H

H

H

H

H

C

C

C C

C

H

H

H

H

H N

O

+ H

C

n

OH

H

H

H

H

C

C

C C

C

H

H

H

H

O C OH

Hexanedioic acid

1,6-diaminohexane

The OH from the acid and the H from the diamine form the water molecule. Peptide bond in red



n

H

H

H

H

H

H

O

H

H

H

H

O

N

C

C

C C

C

N

C

C

C

C C

C

C

H

H

H

H

H

H

H

H

O



+

n

Nylon 6,6 “dimer” molecule

General structure of a diol/glycol monomer :

H

H Water

HO  (CH 2 ) n  OH

General structure of a dialkoinic acid monomer :

HOOC  (CH 2 ) n  COOH

General structure of a diamine monomer :

H 2 N  (CH 2 ) n  NH 2

Remember, for the water molecule that condenses out, the -OH functional group comes from the acid (COOH) while the H comes from the glycol (OH) or amine (NH2) functional groups.

10

x

Describe the structure of cellulose and identify it as an example of a condensation polymer found as a major component of biomass

Beta-glucose (C6H12O6) monomers are cyclic polyalcohols. Cellulose is a condensation polymers consisting of 2000-10 000 beta-glucose monomers joined in a chain. A three-carbon and four-carbon chain are present in a β-glucose monomer. These carbon chains have hydrogen and OH- groups attached. When two beta-glucose molecules react though two alcohol (-OH) groups, a water molecule is condensed put and an O molecule links the two glucose monomers. The bond formed is called a beta-1,2-glycosidic bond (C-O-C). Continued condensation produces cellulose. 6

Beta-glucose molecule:

CH2OH C5

O

H C4 HO

OH

-OH group is above ring plane in β-glucose

C1

OH C3

C2

H

OH

H

Cellulose is a flat, linear and rigid molecule: Beta-1,4-glycosidic bond in red CH 2 O H

CH 2 O H

O



O O

OH OH

OH CH 2 O H

O O

OH

O O

OH OH



OH CH 2 O H

OH

The bulky -CH2OH groups (attached to C5) alternate sides of adjoining glucose molecules. Many of the alcohol groups form strong hydrogen bonds between the chains, accounting for its long, strong fibres, insolubility and resistance to chemical attack. Hydrogen bonding

11

Biomass refers to biological material derived from recently living organisms. Cellulose is a major component of biomass. Most dry plants consist of 50% cellulose. Approximately 5.0 x 1011 tonnes of cellulose is produced each year by plants.

x Identify that cellulose contains the basic carbon-chain structures needed to build petrochemicals and discuss its potential as a raw material

The structure of cellulose can be modified using other chemicals to make synthetic biopolymers such as cellophane, rayon fibres and cellulose acetate films. Unlike conventional polymers, biopolymers are biodegradable. Cellulose is used to make water-soluble adhesives for wallpaper. It is used as an additive in processed foods (e.g. thickeners, stabilizers, emulsifiers, anti-caking agents). Such derivatives include methyl-, carboxymethyl- and microcrystalline cellulose Cellulose can also be converted into biofuels such as cellulosic ethanol. This involves the use of acid hydrolysis or enzymes to convert the cellulose chains into glucose monomers. Fermentation by yeast produces ethanol. Most petrochemicals such as plastics, solvents and refrigerants are manufactured from ethylene derived from petroleum. Cellulose has the potential to replace petroleum as a feedstock for petrochemicals because of its long carbon chain structure. Cellulosic ethanol can be dehydrated using concentrated sulphuric acid to form ethylene.

12

x

Use available evidence to gather and present data from secondary sources and analyse progress in the 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 Biopolymer: Plantic

Organism and processes used 1) Non-gm maize bred with high amylose %. 2) Maize is wet milled, starch extracted and dried. 3) Chemical reagent added to reduce cooking temperature and enhance physical properties. Additives e.g. plasticisers can be added at this stage or other polymers added to form copolymers. 4) The material is extruded into sheets or granules before being sold to other companies.

Property Water soluble, Biodegradable, non-toxic

Environmental-friendly packaging material

Thermoplastic

Moulded for use in: Food trays/containers/cups automobile parts, toys, medical equipment, aerospace, home appliances computer components Direct contact with high moisture foods

Relative durability Low cost (relative to petrochemicals) Freeze-thaw stability

Disposable food packaging Cheap toys Frozen food packaging

sealable, printable and laser etchable

Home appliances Personal music players Mobile phone casing Coatings, bags, packaging, gloves

Anti-static

Sources: http://www.plantic.com.au/ourtechnologies/planticadvantages/

Uses/potential uses

Compatibility with conventional plastics

More durable plastics, weather resistant applications e.g. roofing, water piping

http://www.wisegeek.com/whatis-plantic.htm

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3. Other resources, such as ethanol, are readily available from renewable resources such as plants x Describe the dehydration of ethanol to ethylene and identify the need for a catalyst in this process and the catalyst used

x Describe the addition of water to ethylene resulting in the production of

ethanol and identify the need for a catalyst in this process and the catalyst used

x Process information from secondary sources, such as molecular model kits, digital technologies or computer simulations to model: -the addition of water to ethylene -the dehydration of ethanol

Ethylene and ethanol are easily interchanged by the addition of water (hydration) and removal of water (dehydration). Dilute phosphoric acid or heated ceramics are used as catalysts to hydrate ethylene, producing ethanol. The reaction is an exothermic addition reaction. Hydration of ethylene to form ethanol: H

H C

+

C H

H

O H

Dilute H+ catalyst

H

H

H

H

C

C

H

H

OH

 catalyst ethylene  water H o ethanol  catalyst C 2 H 4(g)  H 2 O (l) H o C 2 H 5 OH (l)

Concentrated acid or phosphoric acid is used to dehydrate ethanol, producing ethylene. This reaction is exothermic so the temperature of the system must not exceed 180˚C, or the ethylene yield is reduced. Dehydration of ethanol to form ethylene and water:

H

H

H

C

C

H

H

H

H OH

C

Concent. H+ catalyst

+

C

H

H

O H

H

 catalyst ethanol H o ethylene  water  catalyst C 2 H 5 OH (l) H o C 2 H 4(g)  H 2 O (l)

14

Countries rich in natural gas e.g. Persian gulf or petroleum reining and cracking facilities e.g. Singapore, can make ethanol via hydration of ethylene Countries rich in land, water and climates suitable for growing crops that can be used to produce ethanol e.g. Brazil, USA can make ethylene via dehydration of ethanol derived from the fermentation of starch crops.

x Describe and account for the many uses of ethanol as a solvent for polar and non-polar substances

The ethanol molecule contains a hydrophilic ‘head’ (-OH) that dissolves polar and ionic substances. Ethanol is completely miscible in water due to hydrogen bonding between the molecules. The short hydrophobic hydrocarbon chain, (CH3CH2) dissolves non-polar molecules such as longer chain alkanols. Thus, ethanol can dissolve both polar and non-polar substances. Industrially, and in consumer products, ethanol is the 2nd most important solvent after water. It is the least toxic of all the alcohols, being toxic in moderate amounts. Ethanol is widely used as a solvent for many medicines, toiletries, food flavourings and colourings that are insoluble in water. Once the non-polar material is dissolved in the ethanol, water can be added to prepare a mostly water solution.

“Water fearing” C chain dissolves non-polar substances

H

H

H

C

C

H

H

OH

“Water loving” OH head dissolves polar and ionic substances

x Outline the use of ethanol as a fuel and explain why it can be called a renewable resource

Ethanol combusts in air, releasing carbon dioxide, water and heat. Because the ethanol molecule contains an oxygen atom, combustion is nearly always complete. There is little formation of carbon monoxide and carbon which form during the incomplete combustion of other hydrocarbons e.g. petrol, octane. However, it has a lower heating value than petrol- 30MJ/kg compared to 27MJ/kg for petrol. It is used as a petrol extender (e.g. gasohol/petranol = 10-20% ethanol) , where it assists the fuel to burn more efficiently.

15

Ethanol can be called a renewable resource because it can be produced by fermentation of plant material. The products of its reaction, carbon dioxide and water are reactants needed by plants to photosynthesise.

x Process information from secondary sources to summarise the processes involved in the industrial production of ethanol from sugar cane

Industrial production of ethanol from sugar cane: sugar cane Crush and grind Hydrolyse with dilute acid e.g. H2SO4 at 100˚C for 2 hours

filter Cellulose + lignin residue

Hydrolyse (more acid)

Filtrate (Sugar solution)

Sugar solution is acidic. Neutralise with i.e. calcium hydroxide [Ca(OH)2] Filter to remove calcium sulfate i.e. gypsum (CaSO4)

Ferment using yeast/bacteria Ethanol mixture

Distillation to produce pure ethanol

Carbon dioxide

By-products and wastes i.e. solid lignin can be used as fuel for the plant 16

x Process information from secondary sources to summarise the use of ethanol as an alternative car fuel, evaluating the success of current usage

Ethanol as a fuel Advantages Disadvantages Renewable resource- from crops such as Large areas of land required to grow corn, sugar cane and wheat crops High cost of: x distillation x removing water from fuel to prevent fuel injection problems and corrosion. Reduction of: Some ethanol based –fuels are more x Greenhouse gases e.g. CO2, NO2, SO2 volatile, leading to increase in x Carbon monoxide (ethanol combustion emission of toxic organic compounds is more complete than other fuels) Combustion produces toxic organic x High-octane antiknock and octane c ompounds which must be removed rating additives used to replace b y catalytic converters in the tetraethyl lead in petrol vehicle’s exhaust system Spills are more easily biodegraded/diluted Spills are difficult to contain and to non-toxic concentrations recover- ethanol mixes with water Evaluation of current success of ethanol as a fuel: Australia currently produces less than 30 million gallons of ethanol from crop sources. It is considered unviable at present and legislation imposes a 10% cap on ethanol-gasoline blends because most vehicle engines cannot tolerate it Ethanol has proved most successful in Brazil with 6500 million gallons produced/year from sugar cane. Brazil’s usage of ethanol is due to its few oil reserves and high pollution rates. In Brazil, ethanol comprises 50% of gasoline fuel sales/year and it is mandatory for fuel blends to contain minimum 20% ethanol. The latest innovation within the Brazilian flexible-fuel technology is the development of flex-fuel motorcycles, costing US $2700. The USA is the world leader in ethanol fuels, producing over 9000 million gallons/year. Its usage is due to increasing environmental concerns and the need for renewable fuels and comprises about 10% total gasoline fuel sales/year. The US uses corn to produce ethanol which is much less efficient than sugarcane and wastes valuable food.

17

x Describe conditions under which fermentation of sugars is promoted Suitable conditions for fermentation: -A suitable microorganism capable of fermenting sugars into ethanol e.g. yeast, E Coli. Bacteria -Water -suitable temperature (25-32˚C for yeast) -low oxygen concentrations -small amounts of yeast nutrients e.g. phosphate salt -Less than 15% alcohol concentration by volume. Once this is exceeded, the yeast dies.

x Solve problems, plan and perform a first-hand investigation to carry out the fermentation of glucose and monitor mass changes

Experiment: Fermentation of Glucose Aim: To plan and perform an experiment to investigate the mass changes during the fermentation of glucose Hypothesis: The loss in mass of the reaction mixture, consisting of water, glucose and yeast will increase gradually initially before increasing rapidly and then reaching an optimal. Equipment: 2 x 500mL conical flasks Rubber stopper with tube attached Water Glucose

Sachet of yeast 500mL beaker Stirring rod Electronic scale

Procedure: 1/ Add 50g glucose to a beaker and dissolve thoroughly in 500mL water using a stirring rod. 2/

Weigh one empty conical flask and rubber stopper.

3/

Place 500mL of glucose solution into the flask.

4/

Add 1.0g yeast to mixture and shake gently to dissolve.

5/

Weigh the flask, stopper and yeast-glucose-water mixture.

6/

Place the other end of the rubber tubing into another flask filled with water. This is to provide an anaerobic condition for the yeast to multiply.

7/

Reweigh the flask, stopper and yeast-glucose-water mixture at set intervals, preferably every hour until the weight does not change anymore. Record the results in the table below. 18

Glucose, yeast water mixture

water

Results: Mass of empty flask= 232.68g Mass of flask + rubber stopper + mass of water-glucose-yeast mixture= 724.30g Mass of water-glucose-yeast mixture= 724.30g-232.68g = 491.62g Time (days) Mass lost (g)

0 0

1 -

2 -

3 1.5

Discussion: The results obtained indicate that the yeast did not react with the glucose mixture. This is probably because the yeast was not properly dissolved or it had expired. To increase the reliability of the results obtained and to help observe any trends, a data logger should be used to record the readings, preferably at intervals of 1 hour for several days, rather than over a single interval of three days as was done. This would allow a trend to be observed when the mass lost is plotted against time on a x-y graph. To take the investigation further, the several variables could be changed: -conduct the experiment under controlled temperatures, both above and below room temperature -alter the ratio of glucose to water -alter the ratio of yeast to glucose-water solution used Conclusion: It was found that the mass changes during fermentation did not change significantly. However, this simply indicated that the fermentation process did not begin most likely because the yeast was not dissolved properly or it had expired.

19

x Summarise the chemistry of the fermentation process present information

from secondary sources by writing a balanced equation for the fermentation of glucose to ethanol

x

Present information from secondary sources by writing a balanced equation for the fermentation of glucose to ethanol

Waste from sugar cane is rich in sucrose (C12H22O11) but uneconomic to separate. If water and yeast are added, the sucrose reacts with the water to produce glucose and fructose (C6H122O6): sucrose  water  o glucose  fructose C12 H 22 O12(aq)  H 2 O (l)  o C 6 H 12 O 6(aq)  C 6 H 12 O 6(aq)

Fermentation can then occur: ermentation glucose/fructose f o ethanol  carbon dioxide ermentation C 6 H 12 O 6 (aq) f o 2C 2 H 5 OH (l)  2CO 2(g)

x Define the molar heat of combustion of a compound and calculate the value for ethanol from first-hand data

The molar heat of combustion is the heat released when 1 mole of a substance is completely combusted to form products in their normal states (solids, liquids, gases) at 100kPa and 25˚C.

20

x 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

Experiment: Comparing the heats of combustion of alcohols Aim: To design and perform an experiment to determine the heat of combustion of ethanol and cyclohexanol. Hypothesis: It is expected that cyclohexanol will have a greater heat of combustion than ethanol. The accepted heats of combustion of cyclohexanol and ethanol are 3811 kJ/mol and 1364 kJ/mol-1 respectively. Equipment: ethanol cyclohexanol 100g water Electronic scale

bosshead and clamp glass funnel retort stand 250mL beaker thermometer matches spirit burner

Procedure: 1) Place ethanol into empty spirit burner using glass funnel and weigh. 2)

Weigh 100g water and place in beaker.

3)

Set up equipment as shown below:

Beaker containing water Spirit burner with alkanol

Retort stand & clamp

4)

Measure starting temperature of water

5) Light spirit burner and wait until water temperature has increased by 20˚C. Quickly extinguish the flame using the cap of the spirit burner. 6)

Calculate the change in temperature of the water and change in mass of ethanol + spirit burner.

7)

Repeat steps 1-6 for cyclohexanol.

21

8)

Repeat experiment at least three times for each alkanol. Average results to calculate the heats of combustion of each alkanols per gram and per mole. Results: Ethanol Trial No. Mass Starting Finish ΔT Starting Finish Mass of water, m temp water temp m a s s o f m a s s o f a lcohol (˚C) (kg) water alcohol + alcohol+ combusted, (˚C) spirit spirit M (g) (˚C) burner burner (g) (g) 0. 1 21. 5 45.0 23.5 283.80 283.07 0.73 1 0. 1 21. 5 46.0 24.5 283.07 282.37 0.70 2 0 . 1 2 2 . 0 4 5 . 0 2 3 . 0 2 8 2 . 1 7 2 8 1 . 5 2 0.65 3 n/a n/a 0.69 Average 0. 1 23.6 Trial No.

1 2 3 Average Alcohol ethanol

Mass water, m (kg)

Starting temp water (˚C)

0. 1 0. 1 0. 1 0. 1 Calculations: ΔH (mCΔT) m= 0.1 kg ΔT= 23.6˚C C= 4.18 kJkg-1K-1 ΔH= mCΔT = 0.1x4.18x23.6 = 9.86 kJ

Cyclohexanol

m= 0.1 kg ΔT= 20.2˚C C= 4.18 kJkg-1K-1 ΔH =mCΔT =0.1x4.18x20.2 =8.44 kJ

21. 0 21. 5 24. 0

n/a

Cyclo-hexanol Finish ΔT (˚C) temp water (˚C) 41.0 42.0 44.0

20.0 20.5 20.0 20.2

Heat of combustion per gram (kJg-1) ΔH= 9.86 kJ M = 0.69 g Heat of combustion/gram = ΔH/M = 9.86/0.69 = 14.3 kJg-1 ΔH= 8.44kJ M = 0.57 g Heat of combustion/gram = ΔH/M = 8.44/0.57 = 14.8 kJg-1

Starting mass of alcohol + spirit burner (g) 279.09 278.38 277.88

Finish mass of alcohol+ spirit burner (g) 278.38 277.86 277.40 n/a

Mass of alcohol combusted, M (g) 0.71 0.52 0.48 0.57

Heat of combustion per mole (kJmol1 ) Heat of combustion/mole = ΔH kJg-1 x molar mass of Ethanol = 14.3 kJg-1 x 46.068 gmol-1 = 659 kJmol-1

Heat of combustion/mole = ΔH kJg-1 x molar mass of cyclohexanol = 14.8 kJg-1 x 100.156 gmol-1 = 1482 kJmol-1

22

Experimental and accepted heats of combustion (kJ/mol) vs Molecular Mass

Experim ental and accepted heats of com bustion (kJ/m ol)

4500 4000 3500 3000 2500 2000 1500 1000 500 0 0

20

40

60

80

100

Mole cula r Ma ss (g)

Discussion: The results obtained for the heats of combustion of cyclohexanol and ethanol were 659 kJmol-1 and 1482 kJmol-1 respectively. The accepted values from the SI data book give the heat of combustion of 1364 kJmol-1 and 3811 kJmol-1 for ethanol and cyclohexanol respectively. These experimental values were less than half of the accepted values for their heats of combustion. Compared to the accepted values for molar heat of combustion, the cyclohexanol and ethanol had fuel efficiency of 38.9 % and 48.3 % respectively. These large differences in experimental and accepted values were mainly due to the fact that not all of the heat produced during the combustion of the alcohols actually heated the water. Most of the heat would have dissipated into the surrounding air and some would have been absorbed by the heating equipment. The fact that the experiment was performed was performed on a cool day would also have contributed to the inaccurate values. The electronic scales used to measure the masses were only accurate to 0.01g . Since relatively small amounts of water and alkanols were used in the experiment, this could also have affected the results. Another reason may be due to incomplete combustion of the fuels- ethanol burns much more efficiently, however, why is why the fuel efficiency was significantly higher than for cyclohexanol. The experiment was performed three times for each alcohol and the results averaged to calculate the values. If the experiment were performed several more times and the results averaged, a more reliable value may have been obtained. However, the main reason for the large difference in values was due to not all the heat actually heating the water i.e. heat was lost to the surroundings. The equipment should be insulated to prevent this heat loss to obtain more accurate results. Ideally, the experiment should be performed using a bomb calorimeter to measure the heat enthalpy. A bomb calorimeter allows the experiment to be performed in a much more controlled environment to give much more accurate results. Conclusion: It was found that cyclohexanol had a greater heat of combustion than ethanol, but both readings were well below the accepted values for the heats of combustion.

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x Identify the IUPAC nomenclature for straight-chained alkanols from C1 to C8

For straight chain alkanols, the number of carbon atoms in a chain is the same prefix as for alkanes, alkenes and alkynes. The middle syllable, ‘an’ indicates the molecule is saturated and suffix ‘ol’ represents the -OH functional group. A number is used to denote the placement of the -OH group. Use the smallest number possible. No number is required for methanol or ethanol as OH- group is on the end carbon atom.

4. Oxidation-reduction reactions are increasingly important as a source of energy x Explain the displacement of metals from solution in terms of electron transfer

Reactions of metals usually involve transfer of electrons. Metals can be arranged in an activity series: Metal K Na Li Sr Ca Mg Al Zn Cr Fe Cd Co Ni Sn Pb Cu Ag Hg Au Pt

Ion K+ Na+ Li+ Sr2+ Ca2+ Mg2+ Al3+ Zn2+ Cr2+ Fe2+ C d2 + C o2 + Ni2+ Sn2+ Pb2+ C u2 + Ag+ Hg2+ Au3+ Pt2+

Reactivity

Extraction

Reacts with water

electrolysis

Reacts with dilute acids

Highly unreactive

Smelting with coke

Heat or physical extraction

24

Active metals will displace less active metals from solution. For example, zinc will displace copper when placed in solution containing copper ions- zinc releases electrons to become ions and copper ions gain electrons and precipitates out as solid copper metal: Zn  o Zn 2  2e  Cu 2  2e   o Cu

.

Cu 2 (aq)  Zn (s)  o Zn 2 (aq)  Cu (s)

x Identify the relationship between displacement of metal ions in solution by other metals to the relative activity of metals

Metals higher in the activity series will displace metal ions in a solution when the metal is placed in the metal ion solution. The more reactive metal forms a metal ion by losing one or more electrons to form a cation. The general equation for this is: M o M n   ne 

Where M is the more reactive metal and n is the number of electrons transferred Metal reactions can be related to the activity series: -metals from K to Ca react with water, forming hydrogen gas -metals from K to Pb react with dilute acids, forming hydrogen gas -metals from Al to Ni require water in the form of steam before reacting

x Account for changes in the oxidation state of species in terms of their loss or gain of electrons

Substances that cause reduction are called reductants and undergo oxidation i.e. they lose electrons easily (e.g. K, Ba) Substances that cause oxidation are called oxidants and undergo reduction i.e. they gain electrons easily e.g. permanganate ion, MnO4-) and dichromate ion, Cr2O72-. Oxidation state rules: -Oxidation involves an increase in oxidation number -Reduction involves a decrease in oxidation number -uncombined elements have an oxidation state of 0 -ions have an oxidation state equal to their charge (e.g. oxidation state of copper ion, Cu2+ is +2) -oxygen in compounds have charge -2 in oxides and -1 in peroxides -hydrogen in compounds have +1 charge with non-metals and -1 with metals -compounds and polyatomic ions have a charge equal to the sum of the oxidation states 25

Memory Aid: OIL RIG Oxidation Is loss Reduction Is Gain x x x

Describe and explain galvanic cells in terms of oxidation/reduction reactions Define the terms anode, cathode, electrode and electrolyte to describe galvanic cells Outline the construction of galvanic cells and trace the direction of electron flow

Redox reactions take place when electrons are transferred from one reactant to another. An example of a redox reaction is placing zinc metal into copper sulphate solution. The half equations for this reaction are: Zn (s)  o Zn 2 (aq)  2e Cu 2 (aq)  2e   o Cu (s) The net reaction is: Zn (s)  Cu 2 (aq)  o Zn 2  Cu (s) Electrons are transferred from zinc to copper- zinc is oxidised (loses electrons) and copper is reduced (gains electrons) to precipitate out as a solid. It is possible to make redox reactions occur through a circuit to generate an electric current- the device used is called a voltaic or galvanic cell. -In a galvanic cell, the oxidant and reductant solutions are separated by a connecting wire (to carry electrons) and a salt bridge (carries charged ions in solution). -A galvanic cell is composed of two half-cells: a reductant half-cell and an oxidant half cell. -Each half-cell consists of a metal electrode and a solution of a salt of the metal. The arrangement ensures the electrons move from the reductant through the external circuit to the oxidant (rather than directly from reductant to oxidant), thus producing electricity. Galvanic cells are devices in where chemical reactions occur to generate electricity Electrodes are the conductors of a cell which connect to the external circuit The anode is the -ve terminal. It is the electrode where electrons flow into the circuit. Oxidation occurs at the anode.

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The cathode is the +ve terminal. It is the electrode where electrons are drawn from the circuit. Reduction occurs at the cathode. Electrolytes are substances that conduct electricity when in solution or molten. Movement of charges: Electrons flow through external circuit

1/ One electrode liberates electrons from the metal electrode into the external circuit Electrode reaction liberates electrons (anode)

2/ Electrons flow through the external circuit via a wire to the other electrode 3/ The reaction at the other electrode use these electrons

Movement of ve charges Movement of +ve charges

Electrode reaction absorbs electrons

(Cathode)

4/ Ions move through the connecting salt bridge to maintain electrical neutrality.

Electron flow

SO42

Zn anode (-ve)

Cu cathode (+ve)

-

Salt bridge Na2SO4 Zn2

+

Oxidation

Cu2

+

Reduction

In the example above, a Zn(s) anode (-ve electrode) is placed in a solution containing SO42- ions. Oxidation takes place at the anode- Zn(s) is transformed into Zn2+ and 2e. Zn2+ moves into the solution and the electrons travel through the connecting wire to the copper cathode (+ve electrode). Reduction takes place at the cathode- the electrons travelling through the wire join with Cu2+ ions in solution to form solid copper metal on the copper cathode. A salt bridge is a U-shaped tube with a porous plug a either end that connects the two solutions to form a complete circuit. It allows negative charges (SO42- in this case) to 27

move from the reductant to the oxidant cell, neutralising unbalanced charges in the solutions. If the redox reaction is allowed to continue, substantial amounts of electricity can be generated and chemical changes occur: -copper metal is deposited on the copper electrode -Zinc electrode dissolves (confirmed by weighing) -Copper ions in solution decrease (blue solution lightens in colour) -Zinc ions increase Electricity produced can be used to turn electric motors, produce heat, light globes. x

Solve problems and analyse information to calculate the Eø of named electrochemical processes using tables of standards potentials and halfequations

oxidant + electron/s reductant Eø Volts + – Li +e Li –3.04 K+ + e– K –2.94 2+ – Ca +e Ca –2.87 + – Na +e Na –2.71 Mg2+ + 2e– Mg –2.36 3+ – Al + 3e Al –1.68 H2O + e– ½H2(g) + OH– –0.83 2+ – Zn + 2e Zn –0.76 2+ – Fe + 2e Fe –0.44 C d2 + + 2e– Cd –0.40 2+ – Ni + 2e Ni –0.24 2+ – Pb + 2e Pb –0.13 H+ + e– ½H2(g) 0.00 + – Cu2 +e Cu 0.34 – ½O2(g)+H2O +e 2OH 0.40 Cu+ + e– Cu 0.52 – ½I2(aq) +e I 0.62 3+ – 2+ Fe +e Fe 0.77 Ag+ + e– Ag 0.80 – ½Br2(aq) +e Br 1.10 ½O2(g)+2H+ + 2eH2O 1.23 – ½Cl2(aq) +e Cl 1.40 – ½F2(g) +e F 2.89 The strongest reductant has the most negative value for its reduction half-equation. It is the most easily oxidised. Lithium metal is the strongest reductant and weakest oxidant The strongest oxidant has the most positive value for its reduction half-equation. It is most easily reduced. Fluorine gas is the strongest oxidant and weakest reductant

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Calculating a potential Eø: The table shows the values for the reduction potentials. To find the oxidation potential, simply switch the sign. Calculating EMFTotal: 1)

Look at the two reduction half equations. The one with the more positive value will occur as shown.

2)

The other half-reaction will be pushed in the opposite direction (oxidation) and the potential standard sign is flipped.

3)

Add the two standard potentials.

To see if a reaction will occur spontaneously: 1) Write both reduction half-equations. 2) Look up the standard potentials in the table above 3) The half-reaction with the more positive value will occur as shown and the other half-reaction and its standard potential will be reversed (oxidation). 4) Add the two standard potentials. If the total voltage is positive, the reaction will occur spontaneously. Example: Does the reaction Ag 2 O  H   Sn  o Ag  Sn 2  H 2 O occur spontaneously? 1 H  (aq)  e   o H 2(g) 2 θ θ EMF E Hg 0.00V Sn (s)  o Sn 2 (aq)  2e  EMF θ

E θ Sn

(0.14)

0.14V

1  1 Ag 2 O (s) H 2 O (l)  e   o Ag (s)  OH  (aq) 2 2 θ θ EMF E Ag 2O 0.34V EMFθ Total

0.00  0.14  0.34

0.48V

EMFTotal is positive. Therefore, the reaction will occur spontaneously.

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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: -Vanadium redox cell, fuel cell, Liquid junction photovoltaic device In terms of: -chemistry -cost and practicality -impact on society -environmental impact Lead-acid cell 1 2 V ( s i x 2 V cells arranged in series) Voltage x

Anode (-) Anode halfequation Cathode (+) Cathode halfequation Overall equation Electrolyte Reaction Additional Info.

Cost and practicality

Impact on society Environmental impact

Porous Pb sheet

Pb (s)  SO 4

2

(aq)

 o PbSO 4(s)  2e 

Lead sheet coated in Lead oxide, Pb(IV)O2 2 PbO 2(s)  SO 4 (aq)  4H   2e   o PbSO 4(s)  2H 2 O (l) PbO 2(s)  2H 2 SO 4

2

(aq)

 o 2PbSO 4(s)  2H 2 O (l)

Sulphuric acid, H2SO4 (35% w/w) (6 molL-1) At the anode, lead ions combine with sulfate ions. Lead sulfate precipitates on the cathode and water is formed as a by-product. -Electrodes have grids to increase surface area Battery life limited by: -over time, cathode (PbSO2) is disintegrated by electrolyte (H2SO4), affecting recharging ability -Corrosion of Pb anode by electrolyte -internal short circuiting due to corrosion As battery is used, electrolyte density drops from 1.26g/cm3 to 1.1g/cm3 as H+ ions are used. A battery hydrometer is used to measure the charge level of the battery. Advantages Disadvantages -Able to be recharged via -Pb content of batteries is expensive. suitable transformer -overcharging can produce explosive H2 -Works in range of temperatures -Heavy and bulky -Low energy density compared to other rechargeable cells -electrolyte is liquid and highly acidic -Provides high surge current required by car motors. Useful as a battery in remote locations. -Can be recharged by connecting to solar panels or generators. -Can be used for emergency lighting. -Recycled to retrieve the lead. -Lead is highly toxic to the environment, causing anaemia in humans. The electrolyte is very acidic and dangerous if split. -Lead-acid cells are sealed to prevent volatile acid fumes from causing corrosion.

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Oxygen-hydrogen fuel cell (PEMFC) Voltage

0.7 V

Anode (-)

Platinum catalyst on graphite coated, ridged paper

Anode half-equation Cathode (+) Cathode half-equation

H 2(g)  o 2H   2e  Platinum catalyst on graphite coated, ridged paper O 2(g)  4H   4e   o 2H 2 O (l)

Overall Equation

2H 2(g)  O 2(g)  4H   o 2H   2H 2 O (l)

Electrolyte Reaction

Solid Fluorocarbon polymer with sulfonic acid groups (The reaction is the opposite of electrolysis i.e. oxygen and hydrogen bond to form water and electrical energy) Hydrogen gas is pumped in at the anode and is oxidised to form protons and electrons. Oxygen gas is delivered to the cathode side. Oxygen molecules react with the protons permeating through the polymer electrolyte membrane and the electrons arriving through the external circuit to form water molecules -The fuels (reductant and oxidant) must be constantly replenished from a reservoir outside the cell. -First developed in 60’s and 70’s for use in spacecraft -Anode and cathode material are the same -Pure H2 must be used or Platinum catalyst is inactivated Advantages Disadvantages -Little thermal -Expensive to produce and maintain shielding is required (H2 fuel is costly) as it operates at only -Contaminated by sulphur containing compounds 85˚C -Ideal for commercial applications e.g. transport

Additional Info.

Cost and practicality

Impact on society Environmental impact

-Developing technology; no short-term impacts -Operating hours (50 000+), efficiency and instant start-up mean it may replace fossil fuel energy sources in the future. -No toxic materials are used and produces only water as byproduct. -Hydrogen is used as a fuel, so storage may be a risk

Evaluation of the PEMFC: Lead-acid cells have proved crucial to the development of modern society in terms of industry, electrical energy and transportation. They do have risks associated with handling and disposal to the environment due to toxic lead and sulphuric acid. They also degrade over time with increased usage and produce waste heat. Despite drawback, it has proved to be one of the most useful devices because of its practicality in a variety of situations and its cost. The PEMFC is a relatively new technology that has the potential to replace lead-acid cells as well as having many other applications. It utilises oxygen and hydrogen gas as 31

fuels, whilst producing only water as a by-product, has a low operating temperature and in excess of 50 000 operating hours. However, it is impractical to use at current times because of the expensive materials used, its design and usage (hydrogen fuel must be very pure for it to function properly & must be stored very carefully) and because society is already adapted to rely on the lead-acid cell. In the future, with the increased need to find cleaner sources of energy, the PEMFC may well prove very useful to society. Similarities in chemistry between lead acid and PEMFC: Both produce water as a by-product Both are can be used many times and are rechargeable Both can produce explosive H2

Voltage Anode Cathode Electrolyte Recharging Energy density Degrades with use? Requires warm-up and/or cooling? Production and maintenance costs Operating hours Size and weight (relative to output) Current/future Applications

Toxic materials Waste Heat

Differences in chemistry between: lead acid PEMFC uses six 2V cells Uses single 0.7V cell arranged in series Lead sheet Platinum catalyst on graphite coated paper Lead dioxide coated lead sheet concentrated (aqueous) solid polymer sulphuric acid connect to a power Fuels (oxygen and hydrogen gas) are source e.g. transformer replenished from an external reservoir Relatively low High Yes No Yes No. Operates at a low 85˚C Cost and Practicality: Cheaper and easier than Much more expensive to buy and PEMFC. Can degrade maintain. Fuels need constant with incorrect usage replenishment and must be very pure Much less operating Operating hours 50 000+ hours, depending on usage and handling Heavy and bulky Small and light Impact on society: starting-up vehicles, A relatively new technology, it may be small portable used in vehicles, mobile phones, power equipment, installations, domestic power, military, lighting & ignition, portable power, landfill treatment industry, useful as emergency battery in If costs can be lowered, PEMFC may remote locations, eventually replace lead-acid cells in transport , Environmental impact: Involves toxic lead and No toxic materials, but storage of sulphuric acid explosive H2 is a risk High Low

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5. Nuclear Materials x

Distinguish between stable and radioactive isotopes and describe the conditions under which a nucleus is unstable

An isotope is defined as atoms of the same element with the same atomic number but different mass number. An isotope of an element, E, is represented by AEZ, where A, mass number: the number of protons + neutrons Z, atomic number: the number of protons Isotopes of the same element have the same atomic number (Z). The spontaneous emission of radiation by certain elements is called radioactivity. For some elements, all isotopes are radioactive while for other, only a few are radioactive. The radioactivity comes from emissions from the nucleus of an isotope. We can use the terms unstable nuclei to describe radioactive isotopes and stable nuclei to describe non-radioactive isotopes. The stability of the nucleus is related to the force that holds the nucleus together, called the strong nuclear force. The strong nuclear force is what keeps all the protons and neutrons together in a nucleus even though they should normally repel due to like charges. Nuclear stability is determined by the ratio of neutrons to protons (n:p). In general: -stable light elements (Z from 1-20) have a n:p ratio of 1:1 -stable heavy elements (Z from 73-83) have a n:p ratio of 1.5:1 For elements with Z>83 (bismuth), there are NO stable isotopes. Radioactive isotopes emit radiation in the form of particles or rays from their nucleus. This decay can occur in a single step or a series of steps e.g. uranium. The time for the radioactivity level of a given amount of radioactive isotope to be halved is called its half-life. Each radioactive isotope has a characteristic half-life. Effect of electric field on radiation:

++++++++++++

β γ

_____________ α particles have +ve charge, so are deflected towards the negative plate. β particles have –ve charge, so are deflected towards the positive plate. γ rays are unaffected.

α

33

Types of nuclear decay: Nuclear Decay Alpha (α) emission

Beta (β)emission

Gamma (γ) emission

Electron capture

Radiation type

Further Info.

Helium nuclei ( 24 He) , positively charged

Ejected from Uranium-238 decays into heavy, unstable thorium-234 238 nuclei to remove o 42 He 23940Th 92 U  surplus protons and neutrons Occurs when n:p Tritium decays into helium-3 3 ratio is too high o 01 e  32 He 1H due to excess neutrons. Electron emission is called (β-) while positron emission is (β+).

Beta particles [high-speed electrons ( 10 e) or positrons (e  ) ]. Released from nucleus when a neutron decays into a proton and electron High-frequency EMR

Removes excess energy without particle rearrangement Often accompanies α and β emissions Occurs when n:p ratio is too low due to excess protons

Inner shell electrons are captured and proton is converted into a neutron Uranium A series of Alpha Uranium-238 and natural decay and beta emissions 235 decay in a series series of emissions into a stable lead isotope

Example

Gamma emission from cobalt-60 as it undergoes beta decay into Nickel-60 60 o 01 e 6208 Ni  γ 27 Co 

Arsenic-73 undergoes electron capture to form Germanium-73 73 0 o 3723 Ge 33 As 1 e  (Net equation) Uranium 235 decays into lead-208. 238 o 20862 Pb  8( 42 He)  6( 01 e) 92 U 

Nuclear decay results in an atom of one type, called the ‘parent’ nuclide transforming to an atom of a different type, named the ‘daughter’ nuclide. x

Describe how commercial radioisotopes are produced

Commercial radioisotopes are those with an atomic number LESS than 92 i.e. radioisotopes smaller than uranium. Commercial isotopes are used in medical and industry purposes. There are two means of producing radioisotopes: nuclear reactors and cyclotrons (a type of particle accelerator). The radioactive properties required determine whether a nuclear reactor or a cyclotron is used to produce a radioisotope.

34

Nuclear reactors allow the uranium chain decay to occur safely, releasing neutrons slowly at a controlled rate. Target atoms are bombarded with neutrons to produce neutron-rich radioisotopes are produced at the nuclear reactor (acronym: NRN) via neutron bombardment. Particle accelerators such as cyclotrons produce neutrondeficient radioisotopes (acronym: NDC) via bombarding the atom with neutrons or other particles e.g. protons, electrons The Australian nuclear society and technology organisation (ANSTO) produces commercial radioisotopes for use in industry, medicine and research. ANSTO operates the research reactor called HIFAR (High Flux Australian Reactor) at Lucas Heights (Sydney) and the National Medical Cyclotron near Royal Prince Alfred Hospital (NSW). The HIFAR reactor has been designed to produce a source of neutrons via the fission of uranium-235. These neutrons can be used to bombard the nuclei of stable elements to form radioisotopes. A stable element is placed in the core of the reactor where it absorbs neutrons and is transformed into a radioactive daughter nuclide.

x

Describe how transuranic elements are produced

Transuranic elements are all elements with an atomic number GREATER than 92 i.e. elements larger than uranium. All are radioactive and have very short half-lives. 22 transuranic elements have been synthesised in particle accelerators or nuclear reactors. The first was Neptunium, produced by bombarding Uranium-238 with neutrons produced in nuclear fission reactors: 238 1 o 23992 U  o 23993 Np 01 e 92 U  0 n  Most transuranic elements are produced in nuclear reactors via neutron or alpha particle bombardment or in linear accelerators and cyclotrons via bombarding existing transuranic elements with smaller nuclei. For example, Iodine-123 is produced in a cyclotron by bombarding xenon-124 with protons: 124 1 o12533 I  2( 01 n)  2( 01 e) 54 Xe  1 p  Transuranic elements with Z>96 are all made by accelerating a small nucleus (such as He, B or C) in a particle accelerator to collide with a heavy nucleus (often of a previously made transuranic element) target. x

Identify instruments and processes that can be used to detect radiation

The properties of radiation are used to detect their levels. The key properties used to detect radiation include the ability to: -darken photographic film -cause electron excitation in certain crystal lattices

35

-Penetrate materials to different extents -Cause ionisation in gases and vapours -Be deflected by electric and magnetic fields All types of radiation cause ionisation of atoms. High energy radiation is highly ionising while low energy radiation is weakly ionising. Alpha radiation is strongly ionising while beta is weakly ionising. Gamma rays are strongly penetrating but weakly ionising. Most radioactive emissions are ionising radiation and are usually detected by a Geiger-Muller tube connected to a counter. The Geiger-Muller tube contains gas that ionises and produces a small pulse of electricity each time it is ionised by radiation. The counter counts the number of pulses. Another device is a cloud chamber which contains a saturated alcohol vapour. The ionisation of the alcohol molecules causes condensation that produces ‘visible tracks’. Alpha particles form straight tracks; beta forms fainter zigzags; gamma rays produce very faint tracks Nuclear industry workers wear badges containing photographic film. The darkening of the film is a measure of their radiation dose. Low energy radiation that is too weak to ionise atoms is called non-ionising radiation and can be detected by a scintillation counter. Non-ionising radioisotopes are mostly used for experiments involving living organisms. The non-ionising radiation emitted transfers energy to a solvent molecule and then to a fluorescent molecule that emits light. The light is converted into an amplified electrical pulse and a counter counts the pulses.

Geiger counter

36

x

Process information from secondary sources to describe recent discoveries of elements

The transuranic elements (Z>92) are among the most recently discovered elements. These elements are produced synthetically as the product of experiments using nuclear reactors or particle accelerators via nuclear fusion or neutron bombardment. Several of these elements (e.g. Americium, Curium) were produced in atomic bomb detonations by the Manhattan project (a secret project conducted by the US during WW2 to develop the atomic bomb). The more recent, heavier elements have been produced by nuclear fusion of elements in particle accelerators. The elements are collided together with high velocities, causing fusion of the nuclei and forming new, unstable elements which decay rapidly. Recent element & atomic number Unquadium, Z=114

Darmstadtium Z=110

Ca-48

First discovered in…

Chemistry of reaction

1999, Dubna Russia by the Joint institute for nuclear research (JLNR).

Produced via collision of calcium-48 ions into plutonium-244 using an ion accelerator: 244 48 292 94 Pu  20 Ca o 114 Uuq Nuclear fusion of lead-208 atoms with nickel-62 ions. A neutron is also produced. 208 269 1 82 Pb  Nio 110 Ds  0 n

4 atoms were detected in 1994, Darmstadt, Germany by the GSI

Uuq-292

Pu-244

Calcium-48 collides with Plutonium-244. Their nuclei fuse to form to form…

Ni-62

Pb-204

Nickel-62 collides with Lead-208. Their nuclei fuse to form to form…

Ununquadium-292!

+

Ds-269

1 neutron & Darmstadtium-269!

37

x x x

Use available evidence to analyse benefits and problems associated with the use of radioisotopes in identified industries and medicine Identify one use of a named radioisotope: -in industry -in medicine Use available evidence to analyse benefits and problems associated with the use of radioactive isotopes in identified industries and medicine.

Radioisotope in medicine: Technetium-99m Metastable form of Tc-99 i.e. does not decay into another element. Chemistry It is a gamma emitter and decays into Tc-99. Half-life = 6 h It is produced in nuclear reactors via bombardment of molybdenum-98 to form molybdenum-99: 98 1 o 9492 Mo 42 Mo  0 n 

Why it is used?

Which then undergoes beta decay to form technetium-99m… 99 o 10 e 9493Tc 41 Mo  Has a range of medical applications. It is reasonably reactive and can be combined with organic molecules that form compounds which concentrate around organs of interest. Has a very short half-life and is low-energy for a gamma emitter.

How it is used?

Benefits

Problems

It is easily removed by the body. (85% of medical radioisotopes used are Tc-99m.) Useful in medicine as a ‘tracer’ to detect and diagnose vascular, bone, heart, thyroid disorders and brain tumours. Technetium-99m is produced on site in a special ‘radioisotope generator’ kit by dissolving in 0.9% w/v sodium chloride solution before extraction for medical use. The generator contains heavy shielding to protect against radiation. A dosage of the solution is injected into a patient and Single proton emission computer tomography (SPECT) is used to scan the patient and detect abnormalities. Unlikely to cause any long-term tissue damage because it is low energy and is easily removed by the body. The alternative, X-rays, are not as penetrating and require high voltage and electricity. Radiation dosage given to patents must be carefully monitored and regular health-checks required for those who work with Tc-99 Short half-life means it must be produced and used on-site

38

Radioisotope in Industry: Strontium-90 It is a beta emitter with a half-life of 28 years and decays into Chemistry Ytrrium-90. It is produced as a by-product of the fusion of uranium and plutonium in nuclear reactors.

Why it is used?

Half-life decay: 9308 Sr o 01 e 9309Yr Long half-life means samples last long in industrial applications.

How it is used?

Beta particles are best for gauging thickness. Alpha is not penetrating enough and gamma is too penetrating Used to gauge thickness in plastic and metal sheeting. Radiation detector

Correct thickness

Normal radiation levels

Beta particles emitted from Sr-90 source

Radiation too high Too thin

Heat generated from its decay can be used as an electricity source in remote locations. Benefits Problems

Long half-life means it can be used for long periods without need for replacement Can contaminate foods such as milk. If ingested/inhaled, Sr-90 replaces calcium in bone, causing leukaemia Long half-life means it remains in the environment for long periods. It is difficult to remove waste nuclear material Prolonged exposure may cause cancer.

Radioisotopes in Society: Nuclear powers stations utilise the decay of U-235 to generate energy for electricity. In industry, radioisotopes are used for detecting flaws in soldered joints. Gamma emitters are used to sterilise food and medical instruments. Beta emitters can be used as thickness gauges. In medicine, gamma emitters are used to detect and diagnose diseases. Alpha and beta emitters are used therapeutically to treat cancers. Some of these are generated in particle accelerators while other are made in nuclear reactors.

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