9701 Chemistry November 2025 Question Paper 34

1 Sodium carbonate can be manufactured using a two‑step process. The first step involves making sodium hydrogencarbonate, NaHCO3, which is then converted into sodium carbonate, Na2CO3, in the second step of the process by the following reaction. 2NaHCO3(s) Na2CO3(s) + H2O(l) + CO2(g)

In this experiment you will determine the enthalpy change, ΔHr, for this reaction. You will do this by calculating the enthalpy changes when separate samples of sodium hydrogencarbonate and sodium carbonate are added to excess hydrochloric acid, HCl (aq). You will then combine these values using Hess’s law. NaHCO3(s) + HCl (aq) NaCl (aq) + H2O(l) + CO2(g) ΔH1 Na2CO3(s) + 2HCl (aq) 2NaCl (aq) + H2O(l) + CO2(g) ΔH2

FB 1 is 2.0 mol dm–3 hydrochloric acid, HCl.

FB 2 is sodium hydrogencarbonate, NaHCO3.

FB 3 is sodium carbonate, Na2CO3.

(a) Method

Experiment 1 • Support a cup in the 250 cm3 beaker. • Use the 25 cm3 measuring cylinder to transfer 20.0 cm3 of FB 1 into the cup. • Weigh the container with FB 2. Record the mass. • Measure the temperature of the acid in the cup. Record this temperature. • Carefully add all of the FB 2, in small portions to avoid acid spray. Stir to dissolve. Record the lowest temperature. • Reweigh the container with any residual FB 2. Record the mass. • Calculate and record the mass of FB 2 used. • Calculate and record the decrease in temperature.

Experiment 2 • Support the second cup in the 250 cm3 beaker. • Use the 25 cm3 measuring cylinder to transfer 20.0 cm3 of FB 1 into the second cup. • Weigh the container with FB 3. Record the mass. • Measure the temperature of the acid in the cup. Record this temperature. • Carefully add all of the FB 3, in small portions to avoid acid spray. Stir to dissolve. Record the highest temperature. • Reweigh the container with any residual FB 3. Record the mass. • Calculate and record the mass of FB 3 used. • Calculate and record the increase in temperature. Keep FB 1 for use in Question 3.

Results I II III IV

[4]

(b) Calculations

(i) Calculate the amount, in mol, of FB 2 that reacts with FB 1 and the amount, in mol, of FB 3 that reacts with FB 1. Experiment 1 Experiment 2 amount of FB 2 = mol amount of FB 3 = mol

[2]

(ii) Calculate the energy changes, in J, for each reaction. Experiment 1 Experiment 2 energy change = J energy change = J

[1]

(iii) Calculate the enthalpy change, ΔH, in kJ mol–1 for each reaction. Experiment 1 Experiment 2 ΔH1 = kJ mol–1

sign value ΔH2 = kJ mol–1

sign value

[2] , ,

(iv) Construct an enthalpy cycle and use Hess’s law to determine the enthalpy change, ΔHr, for the reaction shown.

Show your working. 2NaHCO3(s) Na2CO3(s) + H2O(l) + CO2(g)

(If you were unable to calculate values in (b)(iii) then assume that ΔH1 is +27.3 kJ mol–1 and that ΔH2 is –24.9 kJ mol–1. These may not be the correct values.) ΔHr = kJ mol–1

sign value

[2]

[Total: 11] , ,

2 In this experiment you will determine the percentage by mass of a sodium halide impurity present in a sample of sodium hydrogencarbonate by titration. NaHCO3(s) + HCl (aq) NaCl (aq) + H2O(l) + CO2(g)

FB 4 is an aqueous solution made by dissolving 17.20 g of the impure sodium hydrogencarbonate in each dm3 of solution.

FB 5 is 0.200 mol dm–3 hydrochloric acid, HCl.

FB 6 is methyl orange indicator.

(a) Method • Fill the burette with FB 5. • Pipette 25.0 cm3 of FB 4 into a conical flask. • Add several drops of FB 6 to the conical flask. • Perform a rough titration and 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 all your burette readings and the volume of FB 5 added in each accurate titration. Keep FB 4 for use in Question 3.

Results 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 FB 4 required cm3 of FB 5. [1] , ,

(c) Calculations

(i) Give your answers to (c)(ii) and (c)(iii) to an appropriate number of significant figures.

[1]

(ii) Use your answer to (b) to calculate the amount, in mol, of hydrochloric acid in your mean titre.

amount of HCl = mol

Hence determine the amount, in mol, of sodium hydrogencarbonate present in 25.0 cm3 of FB 4.

amount of NaHCO3 = mol

[1]

(iii) Calculate the mass of sodium hydrogencarbonate present in each dm3 of solution.

mass of NaHCO3 = g

Hence calculate the percentage by mass of the sodium halide impurity in FB 4.

Show your working.

percentage by mass = %

[2]

(d) A student carries out the experiment in Question 1 using the impure sodium hydrogencarbonate dissolved to make FB 4.

State how this affects the value of ΔH1 determined in 1(b)(iii) compared to the value the student would get if pure sodium hydrogencarbonate were used State what assumption you have made about the sodium halide impurity [2]

[Total: 14] , , 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. If any solid is heated a hard‑glass test‑tube must be used. Rinse and reuse test‑tubes and boiling tubes where possible. No additional tests should be attempted. , ,

3 (a) (i) To a 1 cm depth of FB 4 in a boiling tube, slowly add a 1 cm depth of dilute nitric acid. Stir gently until the reaction is complete. Use this solution for your tests.

Select reagents to identify which sodium halide is present.

Record details of the reagents used and your observations.

Identify the sodium halide that is present as an impurity in FB 4.

The formula of the impurity is [2]

(ii) Suggest why it is necessary to add the nitric acid to FB 4 before carrying out your tests in (a)(i) [1]

(b) FB 7 contains a metal cation which is listed in the Qualitative analysis notes.

(i) Place half the sample of FB 7 in a hard‑glass test‑tube. Heat gently at first and then more strongly.

Record your observations [2]

(ii) Use the 25 cm3 measuring cylinder to measure 20 cm3 of FB 1.

Place the remaining sample of FB 7 in a boiling tube and add portions of FB 1 from the measuring cylinder until all the FB 7 has reacted. Stir until the reaction is complete.

Record your observations. Keep this solution for use in (b)(iii) [2]

(iii) Carry out the following tests. For each test use a 1 cm depth of the solution from (b)(ii) in a test‑tube.

Record your observations in Table 3.1.

Identify the metal ion present in FB 7. Table 3.1 test observations Test 1 Add aqueous sodium hydroxide. Test 2 Add aqueous ammonia. Test 3 Add a piece of aluminium foil.

The formula of the metal ion in FB 7 is [4] , ,

(c) FB 8 is an acidified aqueous solution containing a metal cation which is listed in the Qualitative analysis notes.

(i) Carry out the following tests. For each test use a 1 cm depth of FB 8 in a test‑tube.

Record your observations in Table 3.2.

Identify the metal ion present in FB 8. Table 3.2 test observations Test 1 Add aqueous sodium hydroxide. Test 2 Add a 1 cm depth of acidified aqueous potassium manganate(VII).

The formula of the metal ion in FB 8 is [3]

(ii) State the type of reaction between the metal ion in FB 8 and acidified aqueous potassium manganate(VII).

Explain how your observations support your answer [1]

[Total: 15] , , Qualitative analysis notes 1 Reactions of cations cation reaction with NaOH(aq) NH3(aq) aluminium, Al 3+(aq) white ppt. soluble in excess white ppt. insoluble in excess ammonium, NH4 +(aq) no ppt. ammonia produced on warming – barium, Ba2+(aq) faint white ppt. is observed unless [Ba2+(aq)] is very low no ppt. calcium, Ca2+(aq) white ppt. unless [Ca2+(aq)] is very low no ppt. chromium(III), Cr3+(aq) grey‑green ppt. soluble in excess giving dark green solution grey‑green ppt. insoluble in excess copper(II), Cu2+(aq) pale blue ppt. insoluble in excess pale blue ppt. soluble in excess giving dark blue solution iron(II), Fe2+(aq) green ppt. turning brown on contact with air insoluble in excess green ppt. turning brown on contact with air insoluble in excess iron(III), Fe3+(aq) red‑brown ppt. insoluble in excess red‑brown ppt. insoluble in excess magnesium, Mg2+(aq) white ppt. insoluble in excess white ppt. insoluble in excess manganese(II), Mn2+(aq) off‑white ppt. rapidly turning brown on contact with air insoluble in excess off‑white ppt. rapidly turning brown on contact with air insoluble in excess zinc, Zn2+(aq) white ppt. soluble in excess white ppt. soluble in excess 2 Reactions of anions anion reaction carbonate, CO3 2– CO2 liberated by dilute acids chloride, Cl –(aq) gives white ppt. with Ag+(aq) (soluble in NH3(aq)) bromide, Br –(aq) gives cream / off‑white ppt. with Ag+(aq) (partially soluble in NH3(aq)) iodide, I–(aq) gives pale yellow ppt. with Ag+(aq) (insoluble in NH3(aq)) nitrate, NO3 –(aq) NH3 liberated on heating with OH–(aq) and Al foil nitrite, NO2 –(aq) NH3 liberated on heating with OH–(aq) and Al foil; decolourises acidified aqueous KMnO4 sulfate, SO4 2–(aq) gives white ppt. with Ba2+(aq) (insoluble in excess dilute strong acids); gives white ppt. with high [Ca2+(aq)] sulfite, SO3 2–(aq) gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acids); decolourises acidified aqueous KMnO4 thiosulfate, S2O3 2–(aq) gives off‑white / pale yellow ppt. slowly with H+ , , 3 Tests for gases gas test and test result ammonia, NH3 turns damp red litmus paper blue carbon dioxide, CO2 gives a white ppt. with limewater hydrogen, H2 ‘pops’ with a lighted splint oxygen, O2 relights a glowing splint , ,