Chemistry. Technician Notes. AQA AS and A Level. Objectives. Safety! Equipment. Background. Procedure

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1 Practical 1: Make up a volumetric solution and carry out a simple acid base titration AQA AS and A Level Objectives To be able to make a standard solution To be able to carry out a titration using volumetric equipment To be able to carry out titration calculations Wear eye protection. Sodium bisulfate solution is considered an irritant at the low concentrations being produced, but solid sodium bisulfate is corrosive in both anhydrous and monohydrate forms (see CLEAPSS Hazcard 98B). Sodium hydroxide is an irritant. Wear disposable nitrile gloves when handling the solid sodium bisulfate. Background 250 cm 3 volumetric (graduated) flask 250 cm 3 beaker 250 cm 3 conical flask sodium hydrogensulfate (sodium bisulfate) sodium hydroxide solution burette stand and clamp pipette and filler filter funnels weighing boat spatula deionised or distilled water (in a wash bottle) glass rod digital mass balance phenolphthalein indicator eye protection Students need to start by preparing 250 cm 3 of sodium hydrogensulfate solution with a known concentration. This is known as a standard solution. They will use this solution to find the concentration of sodium hydroxide using a titration. Part 1: Prepare a solution of sodium hydrogensulfate with a known concentration Before starting any experimental work, students need to calculate the mass of solid sodium hydrogensulfate (NaHSO 4 ) required to make a solution with a concentration of mol dm 3 and a volume of 250 cm 3. Answers will depend on the type of solid used. The mass of anhydrous solid should be between 2.5 g and 3.5 g. The mass of monohydrate should be between 3.1 g and 3.8 g. 1. A clean, dry weighing boat is placed on top of a pan balance. The balance must be accurate to 2 or 3 decimal places. 2. Students use a spatula to add the calculated mass of sodium hydrogensulfate to the weighing boat. 3. The boat plus contents is re-weighed accurately and the mass recorded. This is known as the precise mass. 4. The sodium hydrogensulfate is poured from the weighing boat into a beaker. 5. Students now re-weigh the weighing boat. It is likely that some traces of sodium hydrogensulfate will be left in the boat. They should use this value to calculate and record the mass of sodium hydrogensulfate transferred to the beaker cm 3 distilled (or deionised) water is now added to the beaker containing the sodium hydrogensulfate, and the mixture stirred with a glass rod until all the solid has dissolved. 7. The contents of the beaker should be transferred to a 250 cm 3 volumetric flask, using a funnel to ensure there is no spillage. A wash bottle should be used to rinse the beaker, funnel and glass rod, and the washings added to the volumetric flask. 1 Pearson Education Ltd 2018

2 Practical 1: Make up a volumetric solution and carry out a simple acid base titration AQA AS and A Level continued 8. Students add distilled water (if necessary) to make up the solution to the graduate mark on the volumetric flask. 9. The contents of the flask are mixed thoroughly by shaking gently. 10. Students calculate the exact concentration of the solution they have produced, using the precise mass of sodium hydrogensulfate in the volumetric flask, and label the flask with the name of the solution and the concentration. Part 2: Determine the concentration of a solution of sodium hydroxide by titration using a sodium hydrogensulfate solution with a known concentration 1. Fill the burette with sodium hydrogensulfate solution. 2. Pipette 25 cm 3 of the standard sodium hydroxide solution into a conical flask and titrate it with the sodium hydrogensulfate solution. Use phenolphthalein as the indicator. 3. Step 2 should be repeated until students have obtained concordant titres. There is a table provided in the lab book for recording results. 4. Teachers should check one of each student s burette readings. 5. Students then calculate and record the mean volume of sodium hydrogensulfate solution used in the titration, recording the results as instructed. 6. The students can now use their results to calculate the concentration of the sodium hydroxide. 2 Pearson Education Ltd 2018

3 Practical 2: Measurement of an enthalpy change AQA AS and A Level Objective To calculate the molar enthalpy change for two reactions and use Hess s Law to determine the enthalpy change for the reactions Wear goggles. 2 mol dm 3 hydrochloric acid is an irritant. Potassium carbonate is an irritant. two test tubes 2 mol dm 3 dilute hydrochloric acid solid potassium carbonate solid potassium hydrogencarbonate (bicarbonate) thermometer able to read up to 50 C or greater polystyrene cup 250 cm 3 or 400 cm 3 beaker burette, clamp and stand stirring rod mass balance (2 d.p.) spatula eye protection 1. Students place approximately 3 g of solid potassium carbonate into a test tube, weighing the test tube and its contents. 2. Using a burette, they dispense 30 cm 3 of 2 mol dm 3 hydrochloric acid into a polystyrene cup, which should be supported in a beaker. 3. Students measure and record the temperature of the acid. 4. Students continue to measure the temperature while adding potassium carbonate to the acid and stirring. The highest temperature reached should be recorded. 5. The empty test tube should be re-weighed. 6. Steps 1 5 are now repeated, using approximately 3.5 g of potassium hydrogencarbonate instead of potassium carbonate. This time, the lowest temperature reached should be recorded. 3 Pearson Education Ltd 2018

4 Practical 3: Investigation of how the rate of a reaction changes with temperature AQA AS and A Level Objectives To calculate reaction rate from the gradient of a graph, measuring how a physical quantity changes over time To know how concentration affects the rate of a chemical reaction To know the techniques that can be used to investigate reaction rates Perform the experiments in a well-ventilated laboratory because sulfur dioxide is toxic. Asthma sufferers should be particularly careful of the sulfur dioxide gas given off during the reaction. Hydrochloric acid should not be heated above 55 C. Do not operate a gas syringe when it is connected to a flask. Wear eye protection. 150 cm 3 of 0.1 mol dm 3 sodium thiosulfate 150 cm 3 of 0.1 mol dm 3 hydrochloric acid two boiling tubes six 10 cm 3 conical flasks two 25 cm 3 measuring cylinders stop clock two thermometers ( 10 C to 110 C) water bath filter paper with a cross marked in the centre hot/boiling water eye protection nitrile gloves Toxic Flammable Background The reaction between sodium thiosulfate and hydrochloric acid can be investigated using the time it takes for a cross to disappear from view. The cross is hidden by the sulfur produced during the reaction. The equation for this reaction is: Na 2 S 2 O 3 (aq) + 2HCl(aq) S(s) + SO 2 (g) + H 2 O(l) + 2NaCl(aq) Throughout this experiment, one boiling tube can be used for the sodium thiosulfate solution and the second can be used for the hydrochloric acid solution. 1. Students measure 10 cm 3 of sodium thiosulfate and pour into one of the boiling tubes. 2. They then measure and pour 10 cm 3 of hydrochloric acid into the second boiling tube. 3. The temperature of each solution should be measured and recorded. 4. Students should place their conical flask on the sheet of filter paper so the cross can be seen clearly from above. 5. They then pour the sodium thiosulfate solution into the conical flask. 6. Students then add the hydrochloric acid solution to the conical flask and start the stop clock. 7. The students should stop the clock when the cross on the filter paper is completely obscured by the precipitate. The experiment should be repeated at several different temperatures between room temperature and 55 C. Students will need at least six different sets of readings. For each temperature: 8. Students repeat steps 1 and 2, then place both boiling tubes in a water bath. They allow the solutions in the boiling tubes to reach the same temperature and record the temperature of each solution. 9. Steps 4 7 are now repeated with the heated solutions. 4 Pearson Education Ltd 2018

5 Practical 4: Carry out simple test tube reactions to identify cations and anions in aqueous solution AQA AS and A Level Objective To carry out simple tests for cations and anions in aqueous solutions Wear eye protection. Tie long hair back. Concentrated hydrochloric acid, sodium hydroxide and concentrated sulfuric acid are corrosive. Concentrated ammonia solution (> 3 mol dm 3 ) is corrosive and an irritant. Use a fume cupboard. Do not inhale vapour. See CLEAPSS Hazcard 6. Nitric acid, hydrochloric acid, acidified potassium dichromate(vi) solution and limewater are irritants. Barium chloride is toxic and an irritant. Ethanol is flammable do not use it near a lit Bunsen burner. Pay attention to the hazard warnings on the tubs and bottles of unknown substances. If anything is marked flammable, do not use or store it anywhere near a lit Bunsen burner. If you need to heat a flammable substance, you must do this by standing the substance in a beaker of hot water. solutions as detailed in the table below potassium chloride solid potassium bromide solid potassium iodide solid concentrated sulfuric acid in dropping bottles test tubes and stoppers test-tube racks delivery tubes pipettes distilled water forceps red litmus paper blue litmus paper kettle water bath Petri dish with lid filter paper small spatula eye protection The following solutions are required for this practical. Concentration Solutions 0.02 mol dm 3 limewater 0.05 mol dm 3 silver nitrate solution acidified potassium dichromate(vi) solution 0.1 mol dm 3 barium chloride solution calcium bromide solution magnesium chloride solution strontium chloride solution nitric acid magnesium sulfate solution 0.4 mol dm 3 sodium hydroxide solution 0.5 mol dm 3 sodium carbonate solution hydrochloric acid 1.0 mol dm 3 sulfuric acid 2.0 mol dm 3 ammonia solution concentrated ammonia solution potassium chloride solution potassium bromide solution potassium iodide solution ammonium chloride lead nitrate solution (or lead ethanoate solution) Remind students that space to record their observations for all these experiments is provided in the Lab Book. 5 Pearson Education Ltd 2018

6 Practical 4: Carry out simple test tube reactions to identify cations and anions in aqueous solution AQA AS and A Level continued Test A: Carbonate ions 1. 2 cm 3 of limewater is poured into a test tube and the test tube placed in a test-tube rack cm 3 of sodium carbonate solution and 2 cm 3 of hydrochloric acid are added to a second test tube. 3. The second test tube is sealed with a stopper and delivery tube. 4. The other end of the delivery tube is inserted into the limewater. 5. Students should record their observations in the space provided in the Lab Book. Test B: Sulfate ions 1. Students place 1 cm 3 of magnesium sulfate into a test tube. 2. The same volume of dilute hydrochloric acid and barium chloride is then added to the tube. Test C: Hydroxide ions 1. Students place dilute sodium hydroxide into a test tube. 2. Red litmus paper is then dipped into the test tube. Test D: Ammonium ions drops of ammonium chloride are put into a test tube. 2. Students then add the same amount of dilute sodium hydroxide solution and the mixture is shaken. 3. The test tube is then gently warmed in a water bath. 4. The fumes are tested by holding a piece of damp red litmus paper in the mouth of the test tube using forceps. Test E: Group 2 metal cations (sodium hydroxide) 1. Students put 10 drops of barium chloride into a test tube. 2. The same amount of dilute sodium hydroxide is added and well mixed. 3. The students add one drop of sodium hydroxide at a time until it is in excess, mixing all the while. 4. The test is repeated a further three times, using strontium chloride, magnesium chloride and calcium bromide in place of the barium chloride. Test F: Group 2 metal cations (sulfuric acid) 1. Students put 10 drops of barium chloride into a test tube. 2. The same amount of 1 mol dm 3 sulfuric acid is added and well mixed. 3. The students add one drop of sulfuric acid at a time until it is in excess, mixing all the while. 4. The test is repeated a further three times, using strontium chloride, magnesium chloride and calcium bromide in place of the barium chloride. 6 Pearson Education Ltd 2018

7 Practical 4: Carry out simple test tube reactions to identify cations and anions in aqueous solution AQA AS and A Level continued Test G: Halide ions (in solid salts) These experiments must be carried out in a fume cupboard. Students should wear gloves at all times. 1. Half a spatula of solid potassium chloride is placed into a test tube drops of concentrated sulfuric acid are added to the test tube. 3. Any gas released should be tested with moist blue litmus paper. 4. Steps 1 3 are repeated with potassium iodide. Any gas released should be tested using filter paper dipped in lead nitrate solution. 5. Steps 1 3 are repeated with solid potassium bromide. Any gas released should be tested using filter paper dipped in acidified potassium dichromate solution. Test H: Halide ions (in aqueous solution) 1. About 10 drops of potassium chloride are put into a test tube drops of dilute nitric acid are added and well mixed drops of silver nitrate solution are added mol dm 3 ammonia solution is added in excess and shaken to mix well. The contents of the test tube should be discarded once students have recorded their observations. 5. Steps 1 2 are repeated. 6. Working carefully in a fume cupboard, an excess of concentrated ammonia solution is added. The contents of the test tube should be discarded once students have recorded their observations. 7. Steps 1 6 are repeated twice more, using potassium bromide and potassium iodide in place of potassium chloride. 7 Pearson Education Ltd 2018

8 Practical 5: Distillation of a product from a reaction AQA AS and A Level Objective To oxidise ethanol and use heating under reflux and distillation as practical techniques Wear splash-proof goggles. Ethanol is flammable. Acidified sodium dichromate is an oxidising agent. It is both corrosive and a carcinogen. Wear disposable nitrile gloves. 2 mol dm 3 sodium hydroxide solution is corrosive (see CLEAPSS Hazcard 91A). 1 mol dm 3 dilute ammonia solution is an irritant (see CLEAPSS Hazcard 6). simple distillation apparatus or Quickfit apparatus acidified sodium dichromate(vi) 0.05 mol dm 3 silver nitrate solution 1 mol dm 3 dilute ammonia solution 2 mol dm 3 sodium hydroxide solution 1 mol dm 3 dilute sulfuric acid nitrile gloves stand and clamp measuring cylinder anti-bumping granules test tube thermometer 250 cm 3 beakers ethanol teat pipette ice-water bath hot-water bath kettle splash-proof goggles Protective gloves must be worn at all times when handling acidified sodium dichromate solution. You may wish to prepare Tollens reagent for the students immediately before the practical. 1. Students carefully add 20 cm 3 of acidified sodium dichromate solution to a 50 ml pear-shaped flask. Cool the flask in an ice-water bath. 2. Students set up the flask for reflux, keeping it in the ice-water bath. 3. The students should add a few anti-bumping granules into the pear-shaped flask. 4. Using a pipette, students add 1 cm 3 ethanol to the reflux condenser, a few drops at a time. Remind students to add the ethanol slowly, and to allow time for the reaction to subside each time before adding more ethanol. 5. When all the ethanol has been added, students should remove the flask from the icewater bath and allow it to warm to room temperature. (This will take approximately 5 minutes.) 6. Students should place the flask in a hot-water bath prepared with boiling water from a kettle. The water bath is kept at boiling point for 20 minutes, using a Bunsen burner. The apparatus is then allowed to cool. 7. Students now distil their product using the distillation apparatus. They will collect 3 4 cm 3 of clear, colourless liquid in a test tube which should then be immersed in cold water in a beaker. 8. Students may now prepare their own sample of Tollens reagent by adding 5 drops of sodium hydroxide solution to 2 cm 3 of silver nitrate solution in a test tube or you may wish to pre-prepare the solution for them. 9. Students should add just enough dilute ammonia solution to this test tube to dissolve the brown precipitate completely. 10. Students now use a water bath to warm the test tube gently drops of the distillate obtained in step 8 are now added. If ethanol has been produced, a silver mirror will appear on the walls of the test tube. 8 Pearson Education Ltd 2018

9 Practical 6: Tests for alcohol, aldehyde, alkene and carboxylic acid AQA AS and A Level Objective To research and carry out tests on alcohols, aldehydes, alkenes and carboxylic acids Wear eye protection. Sodium hydroxide and concentrated sulfuric acid are corrosive. Nitric acid, hydrochloric acid and limewater are irritants. Barium chloride and bromine water are toxic and irritants. Ethanol is flammable do not use it near a lit Bunsen burner. Pay attention to the hazard warnings on the tubs and bottles of unknown substances. If anything is marked flammable, do not use it anywhere near a lit Bunsen burner. If you need to heat a flammable substance, do this by standing it in a beaker of hot water rather than heating directly. Do not provide sodium to the students to use as a test for ethanol. Although this is a common test for alcohols, there is a danger of the students reacting sodium with concentrated sulfuric acid. concentrated sulfuric acid sodium carbonate solution a metal carbonate or hydrogencarbonate (e.g. calcium carbonate) limewater potassium dichromate(vi) solution Fehling s solution bromine water test tubes and bungs water bath delivery tube dropping pipettes ethanoic acid, cyclohexene, ethanal (or propanal) and ethanol (do not use tertiary alcohols) labeled as unknown substances W, X, Y and Z nitrile gloves eye protection Part 1: Research Students conduct their own research into the tests for alkenes, aldehydes, carboxylic acids and alcohols. They then write detailed plans for experiments to test for all four of these compounds, describing how they would conduct the test and the results they would expect. Ensure students reference all sources in an appropriate format. Part 2: Testing for alkenes, aldehydes, carboxylic acids and alcohols Students now carry out their experiments to identify substances W, X, Y and Z, ensuring they take all appropriate safety precautions. 9 Pearson Education Ltd 2018

10 Practical 7: Part A: Measuring the rate of reaction by an initial rate method AQA A Level Objectives To investigate the reaction of iodide(v) ions with hydrogen peroxide in acidic solution and to determine the order of the reaction with respect to iodide ions Wear a lab coat and use eye protection Tie long hair back Background 0.25 mol dm 3 dilute sulfuric acid 0.10 mol dm 3 potassium iodide solution 0.05 mol dm 3 sodium thiosulfate solution (in a shared burette) 0.10 mol dm 3 hydrogen peroxide solution (in a shared burette) starch solution burette white tile funnel stand with burette clamp pipette stop clock paper towels measuring cylinders small (100 cm 3 ) beaker large (250 cm 3 ) beaker stirrer distilled water Clock reactions are good experiments to use when attempting to follow a reaction, because they often involve a sudden change (for example, a colour change, the appearance of a precipitate or the disappearance of a solid). The reaction between hydrogen peroxide and iodide ions is a clock reaction. When these chemicals react, iodine is formed. This iodine reacts with thiosulfate ions, which are immediately changed to iodide ions. This continues until all of the thiosulfate ions have been used up; at this point, the iodine that remains suddenly turns blue-black with starch. Students are given the following reaction equations: H 2 O 2 (aq) + 2H + (aq) + 2I (aq) I 2 (aq) + 2H 2 O(l) 2S 2 O 2 3 (aq) + I 2 (aq) 2I (aq) + S 4 O 2 6 (aq) It is possible to determine the order of reaction with respect to iodine ions by altering the concentration of iodine ions. 1. Students set up a burette with potassium iodide. 2. They add 10 cm 3 hydrogen peroxide to a clean, dry 100 cm 3 beaker. This will be used in step Students now take a clean, dry 250 cm 3 beaker and add: 25 cm 3 sulfuric acid 20 cm 3 distilled water 1 cm 3 starch 5 cm 3 potassium iodide (taken from the burette set up in step 1) 5 cm 3 sodium thiosulfate (taken from the shared burette) The sodium thiosulfate must be added last. Once all the reactants have been added, the mixture should be stirred. 10 Pearson Education Ltd 2018

11 Practical 7: Part A: Measuring the rate of reaction by an initial rate method AQA A Level continued 4. The hydrogen peroxide from step 2 is now added to the 250 cm 3 beaker. A stop clock is started and the mixture stirred. 5. When the mixture turns blue-black, students stop the clock and record the time. 6. The beaker should be rinsed out with distilled water and dried using a paper towel. 7. The experiment is repeated a further four times, using different volumes of reactants in the 250 cm 3 beaker, as shown in the table below. Experiment 2 Experiment 3 Experiment 4 Experiment 5 sulfuric acid 25 cm 3 25 cm 3 25 cm 3 25 cm 3 distilled water 15 cm 3 10 cm 3 5 cm 3 0 cm 3 starch 1 cm 3 1 cm 3 1 cm 3 1 cm 3 potassium iodide 10 cm 3 15 cm 3 20 cm 3 25 cm 3 sodium thiosulfate 5 cm 3 5 cm 3 5 cm 3 5 cm 3 11 Pearson Education Ltd 2018

12 Practical 7: Part B: Measuring the rate of reaction by a continuous monitoring method AQA A Level Objectives To investigate the reaction between magnesium and hydrochloric acid Wear a lab coat and use eye protection 1.0 mol dm 3 hydrochloric acid 3 cm magnesium ribbon strip 50 cm 3 measuring cylinder 100 cm 3 conical flask rubber bung and delivery tube to fit conical flask trough 100 cm 3 measuring cylinder stand, boss and clamp stop clock distilled water 1. Students set up the equipment as shown in the diagram below. delivery tube rubber bung conical flask magnesium ribbon hydrochloric acid stand and clamp inverted measuring cylinder trough water 2. A 3 cm strip of magnesium ribbon is then placed in the conical flask and the stop clock started. 3. Students should record the volume of gas produced every 20 seconds for 3 minutes. 4. The experiment should be repeated with a different concentration of acid. Distilled water is used to alter the concentration. 12 Pearson Education Ltd 2018

13 Practical 8: Measuring the EMF of an electrochemical cell AQA A Level Objectives To construct an electrochemical cell To measure the cell potential of a selection of electrochemical cells Wear eye protection and disposable nitrile gloves. Zinc sulfate is harmful. 1 mol dm 3 iron(ii) sulfate is harmful. Potassium nitrate is oxidising. Note that the recommended concentration of silver nitrate is 0.1 mol dm cm 3 of 0.4 mol dm 3 zinc sulfate solution 50 cm 3 of 0.4 mol dm 3 copper(ii) sulfate solution 50 cm 3 of 1 mol dm 3 iron(ii) sulfate solution 50 cm 3 of 0.1 mol dm 3 silver nitrate solution saturated potassium nitrate solution distilled/deionised water one strip each of zinc, copper, iron and silver sandpaper four 100 cm 3 beakers strips of filter paper about 12 cm long 100 cm 3 measuring cylinder voltmeter (20 V) reading to 2 d.p. connecting wires and crocodile clips 1. Students use sandpaper to clean the strips of zinc and copper. 2. A zinc half-cell is set up by pouring 50 cm 3 of zinc sulfate solution into a 100 cm 3 beaker and standing the strip of zinc in the beaker. V voltmeter copper 3. The copper half-cell is set up by pouring 50 cm 3 of copper(ii) zinc sulfate solution into a separate 100 cm 3 beaker and standing the strip of copper in the beaker. copper(ii) solution 4. Students make an electrical contact between the two beakers zinc sulfate solution salt bridge by joining them with a strip of filter paper dipped in a saturated solution of potassium nitrate, as shown in the Figure A: Experimental set-up diagram. This is known as a salt bridge. 5. The two metal strips are joined with a voltmeter, using the connecting wires and crocodile clips. 6. Students record the cell potential of the [Zn(s) Zn 2+ (aq)] and [Cu 2+ (aq) Cu(s)] system. If the voltmeter gives a negative value, reverse the connections so that it gives a positive value. 7. Steps 1 6 are repeated using the following combinations of metal/metal ion half-cells. Remind students to clean the metal strips with sandpaper before use. [Zn(s) Zn 2+ (aq)] and [Fe 2+ (aq) Fe(s)] [Fe(s) Fe 2+ (aq)] and [Cu 2+ (aq) Cu(s)] [Zn(s) Zn 2+ (aq)] and [Ag + (aq) Ag(s)] [Cu(s) Cu 2+ (aq)] and [Ag + (aq) Ag(s)] Reference data Standard cell potentials for these cells are: [Zn(s) Zn 2+ (aq)] and [Cu 2+ (aq) Cu(s)] = 1.10 V [Zn(s) Zn 2+ (aq)] and [Fe 2+ (aq) Fe(s)] = 0.32 V [Fe(s) Fe 2+ (aq)] and [Cu 2+ (aq) Cu(s)] = 0.78 V [Zn(s) Zn 2+ (aq)] and [Ag + (aq) Ag(s)] = 1.56 V* [Cu(s) Cu 2+ (aq)] and [Ag + (aq) Ag(s)] = 0.46 V* *Assumes the solution of silver ions is 1.0 mol dm 3 13 Pearson Education Ltd 2018

14 Practical 9: Investigate how ph changes when a weak acid reacts with a strong base and when a strong acid reacts with a weak base AQA A Level Objectives To investigate how the ph of a solution of ethanoic acid changes as sodium hydroxide solution is added To investigate how the ph of a solution of hydrochloric acid changes as ammonia solution is added Wear a lab coat and use eye protection. Tie long hair back. 0.1 mol dm 3 sodium hydroxide is an irritant (see CLEAPSS Hazcard 91A). 0.1 mol dm 3 ammonia solution is an irritant (see CLEAPSS Hazcard 6). 0.1 mol dm 3 sodium hydroxide solution 0.1 mol dm 3 ethanoic acid solution 0.1 mol dm 3 hydrochloric acid solution 0.1 mol dm 3 ammonia solution burettes funnels stand and clamp burette clamp small (100 cm 3 ) beaker deionised (or distilled) water in a wash bottle ph meter/probe standard ph buffer solutions at ph 4.0, 7.0 and 9.2 glass stirring rod Part A: Calibrate the ph meter Remind students that to ensure accurate readings, they will need to calibrate their ph meters before using them in the investigation. 1. The ph probe should first be washed in deionised water, shaking off any excess water. 2. Students immerse the ph probe in a ph 7.0 buffer solution, and the ph reading recorded. 3. This process is repeated with other buffer solutions (ph 4.0 and ph 9.2), and the readings also recorded. 4. Students now plot a graph of recorded ph values against the ph of the buffer solutions. They will use this graph to convert experimental values to more accurate values. 14 Pearson Education Ltd 2018

15 Practical 9: Investigate how ph changes when a weak acid reacts with a strong base and when a strong acid reacts with a weak base AQA A Level continued Part B: Measure the ph of the mixture of acid and alkali 1. Students set up a burette with ethanoic acid, then use the burette to place 20 cm 3 of ethanoic acid in a small beaker. 2. A second burette is then set up with sodium hydroxide. 3. A clean, rinsed ph probe is placed in the ethanoic acid beaker. The probe is stirred gently and the ph value recorded. clamp burette containing sodium hydroxide solution tap stirrer ph probe beaker ethanoic acid solution ph meter/ data logger Figure A: Experimental set-up 4. 2 cm 3 of sodium hydroxide solution is then added to the ethanoic acid beaker. The solution is stirred and the ph recorded. 5. Step 4 is repeated until 18 cm 3 of sodium hydroxide has been added. Students stir and record the ph after each addition of sodium hydroxide solution. 6. A small amount (around 0.2 cm 3 ) of sodium hydroxide solution is added to the ethanoic acid beaker, the mixture stirred and the ph recorded. 7. Step 6 is repeated until a further 4 cm 3 of sodium hydroxide solution has been added (22 cm 3 in total). The ph is recorded after each addition of sodium hydroxide solution. 8. Step 4 is now repeated until a further 40 cm 3 of sodium hydroxide in total has been added. Stir and record the ph after each addition of sodium hydroxide solution. 9. The ph probe should be rinsed with deionised water once all measurements have been taken. 10. Steps 1 9 are now repeated but: the weak acid (ethanoic acid) is replaced with a strong acid (hydrochloric acid) the strong base (sodium hydroxide solution) is replaced with a weak base (ammonia solution). 15 Pearson Education Ltd 2018

16 Practical 10: Part A: Preparation of a pure organic solid and test of its purity AQA A Level Objectives To synthesise aspirin from 2-hydroxybenzoic acid To test the purity of aspirin by measuring its melting point Perform the experiment in a well-ventilated room. Wear a lab coat and use eye protection. Wear heat-protective gloves when handling hot equipment. Tie long hair back. Ethanoic anhydride is corrosive. Concentrated sulfuric acid is corrosive. 2-hydroxybenzoic acid is harmful. 10 cm 3 ethanoic anhydride 2 g 2-hydroxybenzoic acid 1 cm 3 concentrated sulfuric acid distilled/deionised water two 10 cm 3 measuring cylinders condenser round-bottom flask stand, clamp and boss two 250 cm 3 beakers dropping pipette ice Bunsen burner, tripod, gauze and safety mat mass balance (2 d.p.) and weighing boat Büchner funnel, Büchner flask, water/ suction pump and filter paper to fit funnel melting temperature apparatus and melting temperature tube water bath 1. Students weigh 2 g of 2-hydroxybenzoic acid and put it into a round-bottom flask. The flask is clamped and suspended in a beaker of water cm 3 of ethanoic anhydride is added to the 2-hydroxybenzoic acid. 5 drops of concentrated sulfuric acid are then added to the mixture in the flask. A condenser should also be fitted onto the flask. 3. Make sure the room is well ventilated. Students now carefully warm the mixture in the water bath using a Bunsen burner, gently swirling the mixture until all the solid has dissolved. 4. The mixture should be warmed for a further 10 minutes. 5. After 10 minutes, the flask is removed from the hot water bath and 10 cm 3 of crushed ice is added, along with some distilled/deionised water to break down any unreacted ethanoic anhydride. 6. The flask is now placed in a beaker of iced water until precipitation appears to be complete. 7. The product is filtered off using a Büchner funnel and suction apparatus. 8. The crystals are now washed with the minimum volume of iced water. 9. Students recrystallise the aspirin in the minimum volume of a mixture of ethanol to water (1 : 3). 10. The mixture is now filtered and dried. 11. Students measure and record the mass of the pure, dry crystals, along with the melting temperature using melting temperature apparatus. 16 Pearson Education Ltd 2018

17 Practical 10: Part B: Preparation of a pure organic liquid AQA A Level Objectives To prepare ethyl ethanoate and purify by distillation Wear a lab coat and use eye protection. Tie long hair back. Glacial ethanoic acid is corrosive. Ethanol is flammable. Sulfuric acid is corrosive. glacial ethanoic acid sodium carbonate anhydrous sodium sulfate ethanol concentrated sulfuric acid anti-bumping granules disposable dropping pipette measuring cylinders small and large beakers 50 cm 3 round-bottom flask condenser (with rubber tubing) clamp, stand and bosses Bunsen burner, heatproof mat, tripod and gauze distilled water separating funnel and stopper boiling tube thermometer (0 100 C) and adapter three-way adapter receiver adapter joint clips balance Part A: Preparation of ethyl ethanoate 1. Working in a fume cupboard, students add the following to a round-bottom flask: anti-bumping granules 10 cm 3 ethanol 10 cm 3 glacial ethanoic acid 10 drops of concentrated sulfuric acid. 2. They now half fill a 250 cm 3 beaker with water and stand the beaker on a tripod and gauze. 3. The round-bottom flask is clamped into the beaker of water. The contents of the flask must be below the level of the water in the beaker. 4. Students set up a condenser on the flask, so the mixture can be refluxed. The condenser must be clamped in place without a stopper. 5. Using a Bunsen burner, students heat the beaker of water until it boils. The mixture should be boiled for 15 minutes, then allowed to cool. Note: For Parts B and C of this procedure, students are required to plan how to isolate and purify ethyl ethanoate. Teachers should check these plans are functional and safe before students attempt the practical work. 17 Pearson Education Ltd 2018

18 Practical 11: Carry out simple test-tube reactions to identify transition metal ions in aqueous solution AQA A Level Objectives To investigate some transition metal compounds Wear a lab coat and use eye protection. Tie long hair back. Sodium hydroxide is an irritant (see CLEAPSS Hazcard 91A). Silver nitrate is an irritant (see CLEAPSS Hazcard 97). Chromium sulfate is harmful. Iron nitrate is harmful. four unknown solutions, labelled Solution 1 to Solution 4 The following solutions are suggested: Solution 1: chromium(iii) sulfate solution Solution 2: iron(iii) nitrate solution Solution 3: copper(ii) chloride solution Solution 4: ammonium iron(ii) sulfate solution 0.4 mol dm 3 sodium hydroxide solution 0.5 mol dm 3 sodium carbonate solution 0.01 mol dm 3 silver nitrate solution 12 test tubes seven dropping pipettes test-tube rack 250 cm 3 beaker access to hot water plentiful supply of distilled or deionised water anti-bumping granules joint clips balance Test A 1. Students label four test tubes They add 10 drops of unknown solution 1 to test tube 1 and record the colour of the solution. 3. They add sodium hydroxide, one drop at a time, until it is in excess, shaking the test tube all the time, and record any observations. 4. Steps 2 and 3 are repeated with the other unknown solutions and test tubes. 5. A large beaker is filled with some freshly boiled water, to create a water bath. 6. All four test tubes are placed in the water bath for about 10 minutes, and any observations recorded. Test B 1. Students label four test tubes 1 4 and add 10 drops of sodium carbonate to each test tube. 2. They add 10 drops of unknown solution 1 to test tube 1, shake gently and record any observations. 4. Step 3 is repeated with the other unknown solutions and test tubes. Test C 1. Students label four test tubes 1 4 and add 10 drops of each unknown solution to the corresponding test tube. 2. They add 10 drops of silver nitrate to each test tube and mix gently. 3. All four test tubes are allowed to stand for about 10 minutes, and any observations recorded. 18 Pearson Education Ltd 2018

19 Practical 12: Separation of species by thin-layer chromatography AQA A Level Objectives To analyse the composition of some common medicines by thin-layer chromatography Wear a lab coat and use eye protection. Perform the experiment in a well-ventilated room. Ethanol is highly flammable. Do not look directly into UV light. ibuprofen tablet paracetamol tablet aspirin tablet caffeine tablet Anadin Extra tablet pestle and mortar weighing boat ethanol ethyl acetate TLC plate capillary tubes developing chamber access to UV lamp Part A: Preparing samples 1. For aspirin, ibuprofen and paracetamol tablets: Students crush the tablet using a pestle and mortar and place it in a weighing boat. Dissolve approximately 0.1 g of the powdered tablet dissolved in 0.5 cm 3 of ethanol. 2. For caffeine and Anadin Extra tablets: Crush the tablet using a pestle and mortar and place it in a weighing boat. Dissolve approximately 0.1 g of the powered tablet dissolved in 7 cm 3 of ethanol. Part B: Thin-layer chromatography 1. Students should draw a pencil line 1 cm from the bottom of the TLC plate, and make five equally-spaced marks along this line. 2. They then use a capillary tube to transfer a drop of each solution prepared in Part A to one of the marks on the line. They should make a note of which solution has been applied to which spot, and then allow the plate to dry. 3. Students put 10 cm 3 of ethyl acetate into a developing chamber. 4. They then put the TLC plate into the developing lid chamber, ensuring the spots of solution are above the level of the solvent, and place the lid on top of the developing chamber. TLC plate developing chamber ethanol 5. When the solvent is about 1 cm from the top of the TLC plate, the plate is removed from the chamber and the solvent front (the level the solvent reached) marked with a pencil. 6. The plate is now placed into a fume cupboard to dry. 7. Once dry, the plate is put under a UV lamp so the spots become visible. Students draw around each spot with a pencil. 8. Students can now calculate the R f value of each spot. R f = distance travelled by substance distance travelled by solvent 19 Pearson Education Ltd 2018

20 AQA AS and A Level Published by Pearson Education Limited, 80 Strand, London, WC2R 0RL. Text Pearson Education Limited 2018 Typeset and illustrated by Tech-Set Ltd Gateshead Original illustrations Pearson Education Limited First published 2018 Copyright notice All rights reserved. The material in this publication is copyright. Activity sheets may be freely photocopied for classroom use in the purchasing institution. However, this material is copyright and under no circumstances may copies be offered for sale. If you wish to use the material in any way other than that specified you must apply in writing to the publishers. Acknowledgements The publishers would like to thank John Kavanagh for his contributions to the text. Note from the publisher Pearson has robust editorial processes, including answer and fact checks, to ensure the accuracy of the content in this publication, and every effort is made to ensure this publication is free of errors. We are, however, only human, and occasionally errors do occur. Pearson is not liable for any misunderstandings that arise as a result of errors in this publication, but it is our priority to ensure that the content is accurate. If you spot an error, please do contact us at resourcescorrections@pearson.com so we can make sure it is corrected.