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9701/31 — Paper 3 Advanced Practical Skills 1

Cambridge Assessment International Education · October/November 2025

DOCUMENTS
CI · QP · MS
TOTAL PAGES
33
QUESTIONS
19
MARKS
40
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WHAT THIS PAPER ASKS YOU TO DO

Question 1PRACTICAL

Redox titration: ethanedioic acid vs manganate(VII)

Heat FA 1 with dilute sulfuric acid to about 70°C, then titrate against acidified potassium manganate(VII) to a self-indicating pale pink end-point, and use the stoichiometry to find x in (COOH)₂·xH₂O.

[15]
  1. 1(a)Perform a rough titration of FA 1 (heated with FA 3) against FA 2, then carry out as many accurate titrations as you need for consistent results. Record all your burette readings and titres.[7]
  2. 1(b)From your accurate titration results, calculate a suitable mean value to be used in your calculations: 25.0 cm³ of FA 1 required ___ cm³ of FA 2.[1]
  3. 1(c)(i)Give your answers to (c)(ii), (c)(iii) and (c)(iv) to the appropriate number of significant figures.[1]
  4. 1(c)(ii)Calculate the amount, in mol, of manganate(VII) ions, MnO₄⁻, in the volume of FA 2 calculated in (b).[1]
  5. 1(c)(iii)Calculate the amount, in mol, of ethanedioic acid that reacts with the manganate(VII) ions in (c)(ii). Hence calculate the concentration, in mol/dm³, of ethanedioic acid in FA 1.[2]
  6. 1(c)(iv)Calculate the relative molecular mass, Mr, of the ethanedioic acid in FA 1.[1]
  7. 1(c)(v)Calculate the value of x in (COOH)₂·xH₂O. Show your working.[1]
  8. 1(d)Explain why it is necessary to add FA 3 in each titration.[1]
Sit this question →Run it on the guided bench →
Question 2PRACTICAL

Thermal decomposition of hydrated zinc sulfate

Heat FA 4 in a crucible to constant mass, then use the mass lost as water of crystallisation to find y in ZnSO₄·yH₂O.

[10]
  1. 2(a)Weigh the crucible with lid, then with FA 4 added, then heat and reweigh after cooling — twice, to constant mass. Record all masses and calculate the mass of FA 4 used and the mass of residue obtained.[5]
  2. 2(b)(i)Calculate the amount, in mol, of anhydrous zinc sulfate residue formed in the decomposition of FA 4, and the amount, in mol, of water of crystallisation lost.[2]
  3. 2(b)(ii)Calculate the value of y in the formula ZnSO₄·yH₂O. Show your working.[2]
  4. 2(c)A student suggests using this thermal decomposition method to investigate the number of moles of water of crystallisation in hydrated ethanedioic acid. The teacher says that this method is unsuitable. Suggest why this method is unsuitable.[1]
Sit this question →Run it on the guided bench →
Question 3PRACTICAL

Qualitative analysis: a mislabelled salt and three manganese oxidation states

Devise your own tests for zinc, sulfate and water of crystallisation on FA 5, then heat solid FA 6 and compare it against FA 7, FA 8 and FA 9 to work out what links them.

[15]
  1. 3(a)(i)A bottle labelled FA 5 is thought to contain hydrated zinc sulfate. Devise and carry out tests to investigate whether zinc ions, sulfate ions and water of crystallisation are present. Record the tests you carry out and the observations you see.[5]
  2. 3(a)(ii)Use your observations in (a)(i) to complete Table 3.1 to show whether Zn²⁺, SO₄²⁻ and H₂O are present in FA 5 (tick if present, cross if not).[1]
  3. 3(b)(i)Heat a few crystals of FA 6 in a hard-glass test-tube until no further gas is evolved. Record all your observations.[2]
  4. 3(b)(ii)To the cooled residue from (b)(i), add approximately 3 cm depth of distilled water and stir. Filter the solution formed into a test-tube. State the colour of the solution.[1]
  5. 3(c)(i)You are provided with aqueous FA 7 (the same solution as FA 2), aqueous FA 8 and solid FA 9. Carry out Test 1 (add hydrogen peroxide) on all three; Test 2 (add aqueous sodium hydroxide, then leave to stand) on FA 8 and FA 9 only; and Test 3 (add aqueous iron(II) sulfate) on FA 7 and FA 8 only. Record your observations in Table 3.2.[4]
  6. 3(c)(ii)Suggest the identity of the metal in FA 6/FA 7, FA 8 and FA 9.[1]
  7. 3(c)(iii)Complete Table 3.3 to suggest the oxidation state of the metal in FA 6/FA 7 and FA 8.[1]
Sit this question →Run it on the guided bench →

What the lab technician is told: exact solutions, concentrations and apparatus to set out. This is where the bench comes from.

QUESTION 1 — SOLUTIONS

Told to the candidate only as concentrations of named FA numbers, not by mass or true identity.

  • FA 1— aqueous ethanedioic acid, (COOH)₂·xH₂O — true concentration 0.0492 mol/dm³ (prepared from 6.20 g/dm³ of the dihydrate, i.e. x = 2, but the candidate must determine x from their own titration)150 cm³
  • FA 2MH— acidified potassium manganate(VII), 0.0200 mol/dm³ KMnO₄ in 0.5 mol/dm³ H₂SO₄150 cm³
  • FA 3MH— sulfuric acid, 1.00 mol/dm³ H₂SO₄100 cm³

QUESTION 1 — APPARATUS

  • 25 cm³ pipette1
  • pipette filler1
  • 50 cm³ burette1
  • burette stand and clamp1
  • funnel— for filling burette1
  • 150 cm³ or 250 cm³ conical flask2
  • 25 cm³ measuring cylinder1
  • 100 cm³ beaker1
  • white tile1
  • thermometer— –10 °C to +110 °C, 1 °C graduations1
  • tripod1
  • gauze1
  • Bunsen burner and means to light it1
  • heat-proof mat1
  • wash bottle of distilled water1

QUESTION 2 — SOLID

  • FA 4CMHN— hydrated zinc sulfate, ZnSO₄·yH₂O3.20 ± 0.20 g

QUESTION 2 — APPARATUS

  • crucible with lid— approximate capacity 15 cm³1
  • crucible tongs1
  • pipeclay triangle1
  • tripod1
  • Bunsen burner and means to light it1
  • heat-proof mat1
  • spatula1
  • stop-clock— accuracy 1 second — for timing the heating stages1
  • balance— single-pan, direct reading, 0.01 g accuracy, weighing to 200 gshared, 1 per 8–12 candidates
  • wash bottle of distilled water1

QUESTION 3 — LABELLED MATERIALS

FA 5's label claims hydrated zinc sulfate; its true identity (hydrated magnesium sulfate) is exactly what the devised tests are meant to catch.

  • FA 5— labelled as suspected hydrated zinc sulfate — actually hydrated magnesium sulfate, MgSO₄·7H₂O2.0 ± 0.1 g
  • FA 6OMHHHN— solid potassium manganate(VII), KMnO₄0.4 ± 0.1 g
  • FA 7MH— acidified potassium manganate(VII) — the same solution as FA 210 cm³
  • FA 8HHN— aqueous manganese(II) sulfate or manganese(II) chloride, 0.10 mol/dm³10 cm³
  • FA 9MH— solid manganese(IV) oxide, MnO₂2.0 ± 0.2 g
  • hydrogen peroxide— 10-volume10 cm³
  • aqueous iron(II) sulfateMH— 0.20 mol/dm³10 cm³

QUESTION 3 — GENERAL QUALITATIVE-ANALYSIS REAGENTS

Available for whatever cation/anion tests the candidate devises in 3(a)(i), on top of the named FA solutions.

  • dilute hydrochloric acid— 2.0 mol/dm³10 cm³
  • dilute nitric acidC— 2.0 mol/dm³10 cm³
  • dilute sulfuric acidMH— 1.0 mol/dm³10 cm³
  • aqueous ammoniaCMHN— 2.0 mol/dm³10 cm³
  • aqueous sodium hydroxideC— 2.0 mol/dm³10 cm³
  • aqueous barium chloride or aqueous barium nitrate— 0.1 mol/dm³10 cm³
  • limewaterMH— saturated aqueous calcium hydroxide10 cm³
  • aqueous silver nitrate— 0.05 mol/dm³10 cm³
  • acidified aqueous potassium manganate(VII)MH— 0.01 mol/dm³ KMnO₄ in 0.5 mol/dm³ H₂SO₄ — a separate, more dilute stock from FA 2/FA 710 cm³
  • apparatus normally used in the centre for testing carbon dioxide with limewater

QUESTION 3 — APPARATUS

  • test-tube8
  • hard-glass test-tube— for heating solid FA 6 directly2
  • test-tube rack1
  • test-tube holder1
  • glass rod1
  • spatula1
  • teat/dropping pipette3
  • funnel— for filtering1
  • filter paper1
  • Bunsen burner and means to light it1
  • heat-proof mat1
  • red and blue litmus papers
  • wooden splints
  • aluminium foil
  • wash bottle of distilled water1
  • pen for labelling glassware1
  • paper towels

⚠ Compounds with water of crystallisation: any number of water molecules is acceptable, provided it is noted in the supervisor's report. FA 7 is the same solution as FA 2, just relabelled and issued in a smaller volume for Question 3.

THE CURATED BENCHES BUILT FROM THIS

Same skills, taught rather than examined — guided step by step, with the apparatus mistakes explained as you make them.

Redox titration: ethanedioic acid vs potassium manganate(VII) →Thermal decomposition: water of crystallisation in hydrated zinc sulfate →Qualitative analysis: a mislabelled salt and three manganese oxidation states →