Cambridge A Level Chemistry 9701 — 2022 Oct/Nov Paper 3 · Variant 1

1 Group 1 elements form salts with ethanedioic acid. These salts are ethanedioates and have the formula (COOM)2•2H2O, where M is the Group 1 metal. Ethanedioate ions react with manganate(VII) ions as shown. 5(COO–)2(aq) + 2MnO4–(aq) + 16H+(aq) → 10CO2(g) + 2Mn2+(aq) + 8H2O(l) You will determine which metal is present in (COOM)2•2H2O by titrating a solution of this salt with manganate(VII) ions. FA 1 is 10.14 g dm–3 aqueous hydrated ethanedioate of metal M, (COOM)2•2H2O. FA 2 is 0.0200 mol dm–3 potassium manganate(VII), KMnO4. FA 3 is 1 mol dm–3 sulfuric acid, H2SO4. (a) Method ● Fill the burette with FA 2. ● Pipette 25.0 cm3 of FA 1 into a conical flask. ● Use the measuring cylinder to add approximately 20 cm3 of FA 3 into the conical flask. ● Place the conical flask on a tripod and gauze and heat carefully until the temperature of the solution is approximately 70 °C. ● Remove the flame. ● Carefully lift the hot conical flask and place it on the white tile under the burette. ● During titrations, add FA 2, slowly at first, until a permanent pale pink colour is formed. The pink colour on initial addition may take several seconds to disappear. ● If the reaction mixture turns brown, reheat it to about 70 °C. If the brown colour disappears, continue with the titration. If the brown colour remains, discard the contents of the flask and begin a new titration. ● Perform a rough titration with FA 2. Record your burette readings in the space below. The rough titre is .............................. cm3. ● Carry out as many accurate titrations as you think necessary to obtain consistent results. ● Make sure any recorded results show the precision of your practical work. ● Record in a suitable form below all your burette readings and the volume of FA 2 added in each accurate titration. I II III IV V VI VII [7] (b) From your accurate titration results, calculate a suitable mean value to be used in your calculations. Show clearly how you obtained this value. 25.0 cm3 of FA 1 required .............................. cm3 of FA 2. [1] (c) Calculations (i) Give your answers to (c)(ii), (c)(iii) and (c)(iv) to the appropriate number of significant figures. [1] (ii) Calculate the amount, in mol, of manganate(VII) ions, MnO4–, in the volume of FA 2 calculated in (b). amount of MnO4– = .............................. mol [1] (iii) Calculate the amount, in mol, of ethanedioate ions that reacted with the manganate(VII) ions in (c)(ii). amount of (COO–)2 = .............................. mol Hence calculate the concentration, in mol dm–3, of ethanedioate ions in FA 1. concentration of (COO–)2 = .............................. mol dm–3 [1] (iv) Calculate the relative formula mass, Mr, of the hydrated ethanedioate, (COOM)2•2H2O. Mr = .............................. [1] (v) Identify M. Show your working. M is .............................. . [2] (d) Explain why it is necessary to add FA 3 in each titration. .................................................................................................................................................... .............................................................................................................................................. [1] [Total: 15] Question 2 starts on the next page.

Mark scheme: Question Answer Marks 1(a) I all the following data recorded 7 • two burette readings and titre for rough titration • initial and final burette readings for two (or more) accurate titrations II titre values shown for accurate titrations and appropriate headings and units in the accurate titration table • initial / start and (burette) reading / volume • final / end and (burette) reading / volume • titre or volume / FA 2 and used / added • unit: /cm3 or (cm3) or in cm3 (for each heading) or cm3 unit given for each volume recorded III all accurate burette readings are to nearest 0.05 cm3 IV the final accurate titre recorded is within 0.10 cm3 of any other accurate titre V, VI, VII award V if  ⩽ 0.60 (cm3) award VI if  ⩽ 0.40 (cm3) award VII if  ⩽ 0.20 (cm3) where  is the difference between the supervisor’s and candidate’s mean titre 1(b) candidate calculates mean correctly to 2 decimal places (dp) 1 • candidate must take the average of two (or more) titres that are within a total spread of not more than 0.20 cm3 • working / explanation must be shown or ticks must be put next to the two (or more) accurate readings selected • the mean should be quoted to 2 dp and be rounded to the nearest 0.01 cm3 1(c)(i) significant figures (sf) 1 all quoted answers in (c)(ii) – (c)(iv) are expressed to 3 or 4 sf 1(c)(ii) correctly calculates amount of MnO4− used 1 0.02  vol in (b) amount of MnO4− = (mol) 1000 1(c)(iii) correctly uses equation and converts volume 1 amount of (COO−)2 that reacted = (c)(ii)  52 (mol) and concentration of (COO−)2 in FA 1 = amount of (COO−)2  100025 (mol dm−3) 1(c)(iv) 1 correctly uses Mr = massmoles Mr = 10.14concentration from (c)(iii) 1(c)(v) identity of M 2 Mr from (c)(iv) − 124 M1: Ar of M = 2 M2: identifies M as being the Group 1 element with the nearest Ar (Li ⩽ 14.9; 15.0 ⩽ Na ⩽ 31.0; 31.1 ⩽ K ⩽ 62.3; 62.3 ⩽ Rb ⩽ 111.4; 111.4 ⩽ Cs ⩽ 250) 1(d) explanation for use of acid 1 to provide H+ and for the reaction (to proceed) / as given in the equation / to acidify the KMnO4

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2 Hydrated copper(II) sulfate, CuSO4•5H2O, can lose its water of crystallisation to form anhydrous copper(II) sulfate. The enthalpy change for the dehydration of hydrated copper(II) sulfate is shown in the equation. CuSO4•5H2O(s) → CuSO4(s) + 5H2O(l) You will carry out experiments to determine the enthalpy changes for the solution of hydrated and anhydrous copper(II) sulfate and then use Hess’s law to determine the enthalpy change of dehydration. FA 4 is hydrated copper(II) sulfate, CuSO4•5H2O. FA 5 is anhydrous copper(II) sulfate, CuSO4. (a) Determination of the enthalpy change of solution of hydrated copper(II) sulfate. Method ● Weigh the container with FA 4. Record the mass. ● Support the cup in the 250 cm3 beaker. ● Use the measuring cylinder to transfer 25.0 cm3 of distilled water into the cup. ● Measure and record the temperature of the water. ● Tip all the FA 4 into the water and stir until the solid dissolves. ● Measure and record the lowest temperature reached. ● Rinse and dry the cup ready for the next experiment. ● Weigh the container with any residual FA 4. Record the mass. ● Calculate and record the change in temperature. ● Calculate and record the mass of FA 4 used. Results [2] (b) Calculations (i) Calculate the energy change during this reaction. energy change = .............................. J [1] (ii) Calculate the amount, in mol, of hydrated copper(II) sulfate, FA 4, used in the experiment. Show your working. amount of CuSO4•5H2O = .............................. mol [1] (iii) Calculate the enthalpy change, in kJ mol–1, when 1.00 mol of hydrated copper(II) sulfate dissolves in water. This is the enthalpy of solution. enthalpy change of solution = ...... ............................. kJ mol–1 [1] sign value (c) Determination of the enthalpy change of solution of anhydrous copper(II) sulfate. Method ● Weigh the container with FA 5. Record the mass. ● Support the cup in the 250 cm3 beaker. ● Use the measuring cylinder to transfer 25.0 cm3 of distilled water into the cup. ● Measure and record the temperature of the water. ● Tip all the FA 5 into the water and stir until the solid dissolves. ● Measure and record the highest temperature reached. ● Weigh the container with any residual FA 5. Record the mass. ● Calculate and record the change in temperature. ● Calculate and record the mass of FA 5 used. Results [1] (d) Calculations (i) Calculate the enthalpy change, in kJ mol–1, for the enthalpy change of solution of anhydrous copper(II) sulfate. enthalpy change = ...... ............................. kJ mol–1 [2] sign value (ii) Use the enthalpy changes calculated in (b)(iii) and (d)(i) to calculate the enthalpy change of dehydration of hydrated copper(II) sulfate. CuSO4•5H2O(s) → CuSO4(s) + 5H2O(l) Show clearly how you obtained your answer. enthalpy change = ...... ............................. kJ mol–1 [1] sign value (e) In the experiments in (a) and (c) you used the same method to determine the enthalpy change of solution of two solids. Tick the box to indicate which statement is correct. Ignore the effect of differences in mass used. The percentage error in (b)(iii) is less than the percentage error in (d)(i). The percentage errors in (b)(iii) and (d)(i) are equal. The percentage error in (b)(iii) is greater than the percentage error in (d)(i). Explain your choice. .................................................................................................................................................... .............................................................................................................................................. [1] [Total: 10] Qualitative analysis For each test you should record all your observations in the spaces provided. Examples of observations include: ● colour changes seen ● the formation of any precipitate and its solubility (where appropriate) in an excess of the reagent added ● the formation of any gas and its identification (where appropriate) by a suitable test. You should record clearly at what stage in a test an observation is made. Where no change is observed you should write ‘no change’. Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. If any solution is warmed, a boiling tube must be used. Rinse and reuse test-tubes and boiling tubes where possible. No additional tests should be attempted.

Mark scheme: 2(a) M1: table of readings with unambiguous headings and correctly displayed units for all entries in the space for Results 2 • (mass of) container + FA 4 • (mass of) container (+ residue) • first / start / initial temperature / temperature of water • lowest / final temperature M2: readings in 2(a) • both thermometer readings shown to 0.0 °C or 0.5 °C • balance readings shown consistently to either 2 dp or to 3 dp • mass and temperature rise in (a) subtracted correctly and shown in the space for results 2(b)(i) correctly calculates energy change 1 energy change = 25  4.18  T fall (J) and answer to 2–4 sf 2(b)(ii) correctly calculates amount of FA 4 1 amount = mass FA 4 249.6 (mol) and answer to 2–4 sf 2(b)(iii) (b)(i) 1 correctly uses (b)(ii) (b)(ii) enthalpy change = (kJ mol−1) (b)(ii) 1000 and + sign and answer to 2–4 sf 2(c) readings 1 mass of FA 5 and temperature rise are correctly calculated two thermometer readings are both above 10 °C temperature rise is greater than T fall in (a) 2(d)(i) correct expressions shown for enthalpy change 2 • energy change = 25  4.18  T change (J) • amount used = mass of FA 5 used159.6 (mol) energy change • H = –1 number of moles  1000 (kJmol ) • negative sign in answer 2(d)(ii) Hess’s cycle calculation 1 correct calculation of H = (b)(iii) − (d)(i) (kJ mol−1) and some working shown e.g., equation as shown and 2 downward arrows with labelling / correct values from (b)(iii) and (d)(i) with correct signs 2(e) explanation for answer selected 1 box 1 ticked: T is larger for (b)(iii) (ora) box 2 ticked: T is the same for both experiments box 3 ticked: T is larger for (d)(i) (ora)

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3 (a) FA 6 is an aqueous solution that contains one cation and two anions. The three ions are listed in the Qualitative analysis notes. (i) Carry out the following tests on FA 6 and record your observations. test observations Test 1 To a 1 cm depth of FA 6 in a boiling tube add aqueous sodium hydroxide, then heat gently. Test 2 To a 1 cm depth of FA 6 in a boiling tube add a 1 cm depth of aqueous sodium hydroxide and a piece of aluminium foil. Heat gently. Test 3 To a 1 cm depth of FA 6 in a test‑tube add a few drops of hydrogen peroxide. [4] (ii) From your observations suggest two possible identities for the cation in FA 6. possible cations: ..................................... and ..................................... [1] (iii) Suggest a test that would allow you to determine which of the cations you suggested in (a)(ii) is present in FA 6. Carry out this test, record the result and hence identify the cation in FA 6. test ...................................................................................................................................... result ................................................................................................................................... The cation present is ....................................................... . [2] (iv) From your observations in (a)(i) suggest two anions that could be present in FA 6 and give their formulae. possible anions: ..................................... or ..................................... [1] (v) Suggest an additional test that could be carried out to confirm the presence of one of the anions you suggested in (a)(iv). Carry out this test, record the result and hence state the identity of the anion. test ...................................................................................................................................... result ................................................................................................................................... The anion present is ....................................................... . [2] (b) Half fill the 250 cm3 beaker with water and heat to approximately 80 °C. Turn off the Bunsen burner. This will be your hot water bath. FA 7 is an organic compound with an Mr between 40 – 57. (i) Carry out Test 2 and Test 3 on FA 7 and record your observations. The result for Test 1 is shown in the table. test observations Test 1 Add a small piece of sodium. no change Test 2 To a 0.5 cm depth of aqueous iodine in a test‑tube add aqueous sodium hydroxide dropwise until the yellow colour just disappears. Then add a few drops of FA 7 and shake the test‑tube. If no change is seen, warm the test‑tube in your hot water bath. Test 3 To a 1 cm depth of FA 7 in a test‑tube add a few drops of acidified potassium manganate(VII). Warm the test‑tube in your hot water bath. [2] (ii) Using the observations in (b)(i) suggest what can be deduced from each test about the functional groups present in FA 7. Test 1 .................................................................................................................................. Test 2 .................................................................................................................................. Test 3 .................................................................................................................................. [2] (iii) Use your deductions in (b)(ii) to suggest the identity of FA 7. FA 7 is ........................................... . [1] [Total: 15]

Mark scheme: 3(a)(i) observations 4 Test 1 M1: NaOH: white ppt and soluble in excess M2: Heat: no change / no (visible) reaction / litmus stays red Test 2 M3: Al: fizz and NH3 / gas turns (damp red) litmus blue Test 3 M4: H2O2: brown / (darker) yellow / yellow-brown / orange-brown / red-brown (solution) 3(a)(ii) possible cations: aluminium / Al 3+ and zinc / Zn2+ 1 3(a)(iii) identifying the cation 2 M1: cation test: add (aqueous) ammonia M2: white ppt soluble in excess NH3(aq) shows Zn2+ 3(a)(iv) possible anions: any two from NO3−, NO2− I− 1 3(a)(v) identifying the anion 2 if iodide in (iv) M1: test: add (aqueous) silver nitrate / AgNO3 M2: yellow ppt (insol in NH3) shows I− if nitrite and nitrate (no iodide) in (iv) M1: test: add (acidified aqueous) potassium manganate(VII) / KMnO4 M2: purple / KMnO4 solution turns (dark) yellow / yellow-brown / orange-brown / red-brown / brown / decolourised shows nitrite OR M1: add named (dilute) acid M2: no fizzing / no brown gas shows nitrate 3(b)(i) M1: Test 2 (triiodomethane test) 2 (Pale) yellow ppt M2: Test 3 add (acidified aqueous) potassium manganate(VII) purple / KMnO4 decolourised 3(b)(ii) any 2 of the following tests correct 2 Test 1: does not contain –OH / not an alcohol / not a carboxylic acid / not hydroxyl group Test 2: contains −CH2C=O (or −CH(OH)CH3) group Test 3: is an aldehyde (or a 1º or 2º alcohol) 3(b)(iii) FA 7 is ethanal / CH3CHO 1

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