Unit 1 Cape Chemistry Lab Manual2013-14

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UNIT 1 CHEMISTRY PRACTICALS 2013 - 2014

Page 2 of 18 TABLE OF CONTENTS Title of experiment Plan and design experiments Qualitative Analysis of Cu2+, Fe2+ and Fe3+ ions Determination of concentration of NaOH Qualitative Analysis of colourless cations Reactivity of metals Chemical Equilibrium Rate of reaction (effect of concentration) Qualitative Analysis of nitrate and halide ions Qualitative Analysis of R Group II Sulphates Enthalpy of Reaction Redox Reaction Rates of reaction (effect of temperature) Ligand Exchange Solubility product of calcium hydroxide

Page number 3 4 6 7 8 9 10 11 12 13 14 15 16 17 18

Page 3 of 18 You are to choose ANY TWO problems listed below and write a full plan and design report on them. Catalysts SBA skills tested: P&D

Module 2

Problem The substance hydrogen peroxide decomposes naturally to water and oxygen gas. You are given THREE substances X, Y and Z and are told that they catalyse the decomposition process of hydrogen peroxide. Your task is to determine which of the three substances is the most efficient catalyst. The format of ALL plan and design reports should be as follows Title Date Hypothesis Chemical principles (theory which would influence your procedure) Aim Apparatus and Materials Procedure Variables Expected results Treatment of results Sources of error / precautions / limitations Brown eggshell vs white eggshell

Skills tested: P&D

Module 1

Problem “Brown egg shells are harder!” “No, you are wrong!” These exclamations are heard by you, a chemistry student as you enter the lab, where other students are waiting for the teacher to arrive. You decided to ask what is going on. After listening to the students who were initially arguing, you then find out that one set of students are claiming that brown egg shells are harder than white egg shells. Devise a hypothesis based on the argument and plan and design an experiment to reject or accept your hypothesis. PX55 vs PX90 Skills tested: P&D

Module 1

Problem For manned exploration of exo-planets (planets not in the Solar System), two new fuels have been developed. PX55 and Px90. Both have similar molar mass and thus weight consideration is not an issue. However, the amount of energy generated by each fuel is the major concern. Devise a hypothesis based on the problem and plan and design an experiment to reject or accept your hypothesis

Baking Powder

Skills tested: P&D

Module 1

You have always observed baking powder being added to flour when a cake is being made. The majority of the time, the cake is nice and fluffy, but on a few occasions, especially when a different brand of baking powder was used, the cake came out flat. Two new brands of baking powder have now appeared on the supermarket shelves:- Blast Off & The Elevator. Both brands have similar prices, so your mother is not sure which one she should buy. You being a CAPE Chemistry student offered to help. Determine which brand would be the more effective as a raising agent in baking.

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Page 9 of 18 Chemical Equilibrium Module: 2

Skills tested: None

In today’s experiment, the effect of changes in concentration in equilibrium systems will be observed. The system studied is: Pink Co(H2O)62+ (aq) + 4Cl- (aq)

Blue CoCl42- (aq) + 6H2O (l)

Procedure 1. 2. 3. 4. 5. 6. 7.

Label three test tubes 1, 2, 3. Equally divide a small amount of 0.2M CoCl2 solution between test tubes 1 and 2. Pour a little concentrated HCl into test tube 1. Stir the contents gently and record observations in Section 2 of the data table. Pour half of the contents of test tube 1 into test tube 3. Add a little distilled water into test tube 1. Stir the contents and records observations in the data table. Add a little AgNO3 to test tube 3. Stir the contents gently and record the results in the data table. Tilt test tube 2 and gently pour a very small amount of the acetone down the side of the tube to avoid mixing the acetone and the cobalt solution. Ensure that the acetone remains in a separate layer to accurate results. Do not write a full lab report, write in the space provided.

Results Step 2

Procedure HCl added

4

H2O added

5

AgNO3 added

6

Acetone added

Observations

Treatment of results 1. In step 2, hydrochloric acid is used as a source of chloride ions. Explain the observations recorded. ……………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………… …………………………………………………………………………… 2. In step 4, why did the addition of water cause the change that it did? ……………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………… 3. In step 5, silver ions from the silver nitrate react with chloride ions to produce an insoluble precipitate. Write the equation for the reaction forming the precipitate and explain the observations. ……………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………… 4. Using the fact that acetone has an attraction for water, explain the observations from step 6. ……………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………

Page 10 of 18 MODULE 2

RATES OF REACTION – EFFECT OF CONCENTRATION

SKILLS TESTED: ORR,AI

Aim: To investigate the effect of concentration on the rate of a reaction Introduction Hydrogen peroxide reacts with iodide ions to form iodine. The thiosulphate ions react with iodine H2O2 + 2H+ + 2I-  I2 + 2H2O 2S2O32- + I2  2I- + S4O62The initial rate of the oxidation of the iodide ions by the hydrogen peroxide in acid solution is found by measuring the time taken to liberate sufficient iodine to react with the thiosulphate ins present, and then to produce a blue colour with starch solution. Procedure Using pipettes and burettes, place the following volumes of solutions in suitable containers The order in which the reagents are added to the container IS VERY IMPORTANT! Please add the reagents in the following order: 1. Sodium thiosulphate 2. Potassium Iodide 3. Water 4. Starch 5. Sulphuric acid 6. Finally the hydrogen peroxide Experimen t#

Sulphuric acid cm3

Starch solution cm3

Water cm3

potassium sodium iodide solution thiosulphate cm3 solution cm3 1 10 1 20 5 5 2 10 1 15 10 5 3 10 1 10 15 5 4 10 1 5 20 5 5 10 1 0 25 5 When you are ready to time a run, add 10 cm3 of hydroxide peroxide from a pipette. Start timing when half has been added and record the time taken (in seconds) for the blue colour of the starch-iodine complex to appear. Remember to rinse containers provided thoroughly with both tap water and distilled water and dry the bottom before starting a new experiment run. Construct a suitable table for the recording your results. Write a full lab report. Treatment of results 1. Construct a suitable table with experiment #, time, volume of potassium iodide and 1 time 2. On the graph paper provided plot a graph of 1 on y axis against volume of potassium iodide on x axis time Draw the best fit straight line through the points. 3. What conclusion can you draw about the effect of changing the concentration of the iodide ion on the rate of the reaction and give a reason for your answer. 4. With REASON, state the order of the reaction with respect to potassium iodide. 5. If you were given a graph using the concentration of potassium iodide vs time, explain how you can use this to confirm the order of reaction that you have stated in question 4 above.

Page 11 of 18 MODULE 3

Qualitative Analysis of NO3-, Cl-, Br-, I-

SKILLS TESTED: NONE

Use no more than 2 cm3 of test solution for each test All observations are to be recorded in tabular form ( tests and observations and inferences). Please note that the inferences must contain the identity of any precipitate formed and the ionic equation(s) for any positive reaction(s). Do not write a full lab report NO3-(aq) 1. Add Devarda’s alloy followed by aqueous sodium hydroxide then warm the mixture. Test any gases with moist red and blue litmus. 2. Add copper turnings, then concentrated sulphuric acid and warm carefully. Cl-(aq), Br-(aq) and I- (aq) The following tests must be carried out on each of the halide solutions except for test 5 which uses the SOLID samples. 3. Add lead(II) nitrate solution to each halide ion. Divide the mixture in half. a) To one portion add dilute nitric acid. b) To the second portion add distilled water to the mixture, heat and then allow to cool. 4. Add silver nitrate solution, followed by a little dilute nitric acid and then dilute aqueous ammonia 5. Add concentrated sulphuric acid CAREFULLY to the SOLID SAMPLES. Please be advised that these gases have a strong smell and care must be taken by all persons involved. Test any gases evolved with moist blue and red litmus. Do as a demonstration. Treatment of results 1. What is noticeable about the lead(II) halides solubility in warm or hot water? 2. What is the role of dilute nitric acid be added before the aqueous ammonia in test 4 and why must dilute nitric acid be used as opposed to hydrochloric or sulphuric acid? 3. For the reaction of concentrated sulphuric acid and the solid iodide, there is a smell of rotten eggs. What chemical is responsible for this smell and give an explanation why this substance would have been produced if the sample is a solid iodide.

Page 12 of 18 Qualitative Analysis of R Module: 3

Skills tested: ORR, A&I

Solid R contains one cation and two anions. INSTRUCTIONS: Complete the table below, performing the tests listed and add the observations and inferences for each test. Do not write a full lab report. Tests 1. Describe solution R

Observations

Inferences

2. Use a 2cm3 sample of solution R and add aqueous sodium hydroxide slowly until in excess

3. Repeat step 2 using aqueous ammonia instead of sodium hydroxide solution

4. To a 2 cm3 sample of solution R add a small amount of lead(II) nitrate solution 5. Use a 2cm3 sample of solution R and add a small amount of dilute nitric acid then aqueous barium chloride solution. 6. Use a 2 cm3 sample of solution R and add a small amount of silver nitrate solution followed by aqueous ammonia. Cation present in R…………..………..

Anions present in R……………..

Page 13 of 18 Module 3

Group II sulphates

Skills tested: ORR, AI

Aim: To determine the trend of solubility of group II sulphates Procedure Using a burette place 3 cm3 of each of the aqueous ions in a separate test-tube. Then add an equal volume of sulphate ions using another burette to each of the three test tubes. Allow to stand for 5 minutes. Then using a ruler, measure and record the height of the precipitate in mm (if any) as well as the colour of the precipitate. 5. Record your results in tabular form. 6. Write a full lab report 1. 2. 3. 4.

Treatment of results 1. Construct a suitable table with appropriately labelled columns with units to record the results. 2. Draw an appropriate graph to illustrate the trend of the heights of the precipitates for each of the group II sulphates. 3. Based on the results, give the DECREASING order of solubility of the sulphates. 4. Strontium ions were not available for this experiment, however if they were used, suggest a reasonable value for the height of the resulting precipitate that would have formed. 5. Write a balanced ionic equation with state symbols for any ONE of the reactions. 6. Give the steps of an alternative procedure that can be used to determine the trend of solubilities of group II sulphates.

Page 14 of 18 MODULE 1

ENTHALPY OF REACTION

SKILLS TESTED: M&M

Aim: To determine the enthalpy of the reaction CaO(s) + CO2(g)  CaCO3(s) Introduction The enthalpy change of the above reaction cannot be determined experimentally, thus Hess’s Law will be applied to achieve this objective. Two reactions will be conducted and via Hess’s Law, the enthalpy change of the above reaction will be determined. Both calcium oxide and calcium carbonate will be reacted with dilute hydrochloric acid and the enthalpy changes of those reactions will allow one to achieve the aim of this experiment. Procedure 1. Measure 1g of calcium oxide using a suitable weighing vessel and place in a calorimeter. 2. Measure 50 cm3 of 1M HCl and allow three minutes to pass and then measure and record its temperature. 3. Pour the acid quickly but carefully into the calorimeter and stir the mixture with the thermometer and record its final temperature. 4. Repeat steps 1-3 using calcium carbonate instead of calcium oxide. 5. Do not write a full lab report. Results Place your results in the table below Temperature (°C) Acid used with calcium oxide Resulting mixture from reaction of calcium oxide and acid Acid used with calcium carbonate Resulting mixture from reaction of calcium carbonate and acid Treatment of results 1. Calculate the # of moles of i) calcium oxide used ii) calcium carbonate used 2. Calculate the enthalpy change of the reaction involving i) calcium oxide ii) calcium carbonate Given that the heat capacity of the solution is 4.18 J g -1 °C-1 and that 1 cm3 of aqueous solution has a mass of 1g 3. Using your answers to questions 1 and 2, determine the enthalpy change of reaction for i) one mole of calcium oxide ii) one mole of calcium carbonate 4. Draw an energy cycle for the enthalpy change of the reaction CaO(s) + CO2(g)  CaCO3(s) using the TWO BALANCED chemical equations for the reactions you have conducted. 5. Use the energy cycle and your answers from question 3 to determine the enthalpy change of the reaction CaO(s) + CO2(g)  CaCO3(s) for one mole of calcium carbonate.

Page 15 of 18 MODULE 2 AIM:

REDOX TITRATION

SKILLS TESTED: M&M, A&I

To determine the concentration of a solution of hydrogen peroxide

Introduction Your task is to use 0.020 moldm-3 potassium manganate (VII) solution to find the actual concentration of a solution of hydrogen peroxide, H2O2, which is believed to have partially decomposed. Procedure 1. Prepare 250 cm3 of a solution of hydrogen peroxide by adding 7.5 cm3 of the stock solution supplied to the volumetric flask and diluting to the required volume. 2. Pipette 25.0 cm3 of this solution into a conical flask. 3. Add 10 cm3 of 1 mol dm-3 sulphuric acid in a measuring cylinder. 4. Titrate the mixture against the potassium manganate (VII) until a permanent pale pink colour appears in the conical flask. 5. Record the titre volume and repeat until concordant values are obtained. 6. Do not write a full lab report, write your results in the table below and answer the questions that follow. Results Burette Reading/cm3 Final

Trial

1

2

Initial Volume used/cm3

Treatment of results 1. Write the relevant half equations for i) the reduction of MnO4- ions to Mn2+ in acidic solution ii) the oxidation of H2O2 to O2 in acidic solution 2. Using the two half equations from question 1, write the full balanced ionic equation. 3. If the stock solution of hydrogen peroxide had a molar concentration of 1.67 mol dm -3, determine the molar concentration of the hydrogen peroxide solution prepared by you. 4. Determine the molar concentration of the hydrogen peroxide solution prepared by you using your titration results. 5. Determine the error in your results. 6. Hydrogen peroxide is sold using terms such as “20-volume”. This means that 1cm 3 of hydrogen peroxide would produce 20 cm3 of oxygen upon decomposition. Using the molar concentration of the stock solution of 1.67 mol dm-3, determine what designation you would assign this hydrogen peroxide.

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Rates of Reaction

Module 2

Skills tested: M&M, ORR

Aim: To determine the effect of temperature on the rate of a chemical reaction and the value of activation energy of the reaction Procedure 1. Measure 20 cm3 of 2M HCl and then measure 5 cm3 of water and pour both into the beaker provided. 2. Simultaneously add the strip of magnesium metal to the acid and start the stop-watch. 3. Stop recording the time as soon as all of the metal strip has dissolved. 4. Discard the mixture and wash the beaker thoroughly with tap water and then with distilled water. 5. Repeat step 1, then setup up a water bath and heat the water to 50 °C. 6. Quickly remove the beaker and place on the counter, allow the temperature to drop to 45 °C and simultaneously add the magnesium strip and start the stop-watch and again stop when all the metal has dissolved and repeat step 4. 7. Repeat the experiment 3 more times, raising the temperature by 10 °C as shown in the table below. 8. Write a full lab report. Results Copy and complete this table to use in your full lab report Experiment # Temperature /°C Time (s) 1 room temp. (please note the temperature of the mixture) 2 3 4 5

45 55 65 75

Treatment of results 1. Based on your results, state the effect of concentration on rate of reaction and give a suitable explanation for your results. 2. Complete the table by calculating i) 1/time ii) the temperature in Kelvin iii) 1/T (K-1) iv) ln rate (which is the ln of the value 1/t) for each of the experiments Experiment # 1 2 3 4 5

Temperature (K)

1/K (K-1)

1/t (s-1)

ln (1/t)

Page 17 of 18 3. Plot a line of best fit of ln 1/t vs 1/K and calculate the gradient of the line. 4. The gradient of the line corresponds to the formula – EA where EA is the activation energy and R is the molar gas R constant 8.314 J K-1 mol-1. Use the gradient of the line to calculate the activation energy for the reaction of magnesium metal and dilute HCl.

Ligand Exchange Module: 3 Aim: To demonstrate the process of ligand exchange

Skills tested: ORR, A&I

Introduction Transition metal ions in aqueous solution form complexes. However depending on amount of a competing ligand and its stability constant, ligand exchange can occur with an accompanying colour change. Procedure 1. Add 3 cm3 of aqueous Cu2+ ions to a test-tube. Record its colour 2. Add conc. HCl slowly to the test-tube until no further change occurs. Record all observations. 3. Decant about ¾ of the mixture and then add distilled water slowly until no further change occurs. 4. Add 3 cm3 of aqueous Fe3+ ions to a test-tube. 5. Add a small volume of ammonium thiocyanate to the test tube and record observations. 6. Repeat test 3 using the mixture obtained from test 5 7. Complete the table below. No full lab report is required. Results Test Observations 1 2

Inferences Write the most likely formula for the complex ion present ………………………………………….. Give the formula of the complex ion present when no further change occurs

3

…………………………………………….. Formula of complex ion that remains when no further change occurs

4

……………………………………………. Write the most likely formula for the complex ion present

5

………………………………………….. Give the formula of the complex ion present when no further change occurs

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…………………………………………….. Give the formula of the complex ion present …………………………………………….

Questions 1. Comment on the magnitude of the differences of the complexes formed in test 1 and test 2. As well as for test 4 and 5. Refer to ease of reversibility of complexes and thus stability constants. 2. Carbon monoxide is poisonous to humans. With reference to stability constants, oxygen and haemoglobin, explain why this is so, and suggest what can be done for a person who has suffered mild carbon monoxide poisoning. Determination of solubility product of calcium hydroxide Module: 1/2

Skills tested: None

Introduction The equilibrium between solid calcium hydroxide and its ions in an aqueous solution is The concentration of hydroxide ions can be determined by titration with hydrochloric acid; the concentration of calcium ions can be calculated from the titration result. Procedure 1. Filter the saturated solution, allowing the first 5 cm3 to run to waste and collecting the rest in a dry beaker. 2. Pipette 25 cm3 of the solution to a conical flask and add few drops of phenolphthalein. 3. Titrate the solution with hydrochloric acid until the first drop turns the solution colourless. 4. Repeat the titration until consistent results are obtained. 5. Write a full lab report. Treatment of results 1. Construct a suitable table with all burette readings for your titration. 2. Write a balanced equation for the reaction of hydrochloric acid and calcium hydroxide. 3. If the molar concentration of the acid is 0.1 mol dm-3, then use the average titre volume to determine - the # of moles of H+ ions present in the reaction mixture - the # of moles of OH- ions present in the reaction mixture - the molar concentration of OH- ions 4. Use the formula of calcium hydroxide to determine the molar concentration of calcium ions present 5. Determine the Ksp of calcium hydroxide and include the accepted Ksp value of calcium hydroxide from a data book or an internet source. Questions: 1. The saturated solution was obtained by adding 4 g of solid calcium hydroxide to 150 cm3 of water and stirring and it was set aside for several days. Why the solution need to be set aside for several days? 2. Why the solution should be saturated? 3. Explain how a saturated solution can also be dilute. 4. Would calcium hydroxide be more or less soluble in the presence of 0.1 moles of NaOH? Explain your answer fully.