OCR A Level Chemistry A: Practical skills assessed in the practical endorsement (H432) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover section 1.2 (statements 1.2.1 and 1.2.2, and the Practical Endorsement rules in section 5g) of the OCR A Level Chemistry A (H432) specification, Version 3.1 (May 2026), for first assessment in 2017. H432 is the full A level, so no question is labelled AS or A2. The endorsement itself is teacher assessed in the lab; these written questions practise the technique knowledge that 1.1.2(a) also brings into the written papers.

Work through the study guide or the revision notes before you start. Other H432 topics are on the OCR A Level Chemistry hub, and every statement is on the printable checklist.

Questions

1. (a) State how a Practical Endorsement result is reported on the certificate. [1] (b) State the minimum number of assessed practical activities needed for a Pass, and which Practical Activity Groups they must cover. [2]

2. You prepare cyclohexene by heating cyclohexanol with concentrated phosphoric acid and distilling off the product. Cyclohexene is highly flammable; concentrated phosphoric acid is corrosive. For each substance, state the risk and a specific control measure. [4]

3. You need 250.0 cm³ of 0.0200 mol dm⁻³ potassium iodate, KIO₃ (M = 214.0 g mol⁻¹). (a) Calculate the mass of solid needed. [1] (b) Describe how to make up the standard solution from the weighed solid. [4]

4. 2.428 g of sulfamic acid, H₃NSO₃ (M = 97.1 g mol⁻¹), a monoprotic strong acid, is made up to 250.0 cm³. 25.0 cm³ portions are titrated with sodium hydroxide. Titres / cm³: 24.80 (rough), 24.35, 24.55, 24.45, 24.40. (a) Calculate the mean titre. [2] (b) Calculate the NaOH concentration, in mol dm⁻³. [3] (c) The pipette is ±0.04 cm³ and each burette reading ±0.05 cm³. Calculate the percentage uncertainty in the pipette volume and in the mean titre. [2] (d) State a suitable indicator. [1]

5. 0.0350 g of lithium reacts with water: 2Li + 2H₂O → 2LiOH + H₂. Take Ar(Li) as 6.9; one mole of gas occupies 24.0 dm³ at RTP. (a) Find the hydrogen volume produced, in cm³. [3] (b) Suggest suitable apparatus to collect and measure the gas. [1]

6. (a) Explain why an organic reaction mixture is heated under reflux rather than in an open flask. [2] (b) State where the thermometer bulb and the water inlet go when distilling the product. [2]

7. 4.60 g of a crude organic solid is recrystallised from hot water. 3.52 g of dry crystals is obtained. (a) Describe the recrystallisation. [4] (b) Calculate the percentage recovery. [1] (c) Use these data: the pure compound melts at 122 °C. The crude solid melted at 117–120 °C; the crystals at 121–122 °C. Explain what the results show. [2]

8. On a TLC plate the solvent front moves 8.4 cm. A sample gives two spots, at 4.2 cm and 2.1 cm. A standard of compound A, on the same plate, has Rf 0.50. (a) Work out Rf for both spots. [2] (b) State what you can conclude. [1] (c) Give two reasons why the baseline is drawn in pencil above the solvent level. [2]

9. A white solid may contain ammonium, sulfate and bromide ions. Describe tests, in a suitable order, with expected positive observations. [5]

10. Use these values: Cu²⁺/Cu +0.34 V; Ni²⁺/Ni −0.25 V. (a) Calculate the standard cell potential. [1] (b) Describe how to set up the cell and measure its voltage. [3]

11. A and B react to form iodine. In a clock reaction, a fixed small amount of thiosulfate and starch is included, and t is the time until the blue-black colour appears.

Run	[A] / mol dm⁻³	[B] / mol dm⁻³	t / s
1	0.050	0.10	84
2	0.100	0.10	42
3	0.100	0.20	21

(a) Explain why the initial rate here is proportional to 1/t. [1] (b) Deduce the order with respect to A and to B. [2] (c) Write the rate equation. [1] (d) Describe a continuous monitoring method for a different reaction that gives off a gas, and how you would find the initial rate. [3] (e) State one way software helps process these results. [1]

12. Three unlabelled 0.0500 mol dm⁻³ solutions are nitric acid, propanoic acid (Ka = 1.3 × 10⁻⁵ mol dm⁻³) and potassium hydroxide. Use Kw = 1.00 × 10⁻¹⁴ mol² dm⁻⁶. (a) Calculate the expected pH of each. [3] (b) Describe how to calibrate the pH meter. [2] (c) Explain why a pH meter is better than a universal indicator chart here. [1]

Answers

1. (a) Separately from the A level grade, as Pass or Not Classified [1] (b) At least 12 [1]; covering all of PAG1 to PAG12 [1] Examiner insight: Both parts of (b) are separate points; giving the number without the PAG coverage earns only one mark.

2. Cyclohexene vapour could ignite [1]; heat with an electric heater, no flames nearby [1]. Phosphoric acid could burn skin or eyes if spilled [1]; wear goggles and gloves and add it slowly [1]. Examiner insight: A control measure gains credit only when it is linked to the named hazard, so “take care” scores nothing.

3. (a) 0.0200 × 0.2500 × 214.0 = 1.07 g [1] (b) Dissolve the solid in distilled water in a beaker [1]; transfer to a 250 cm³ volumetric flask with rinsings of beaker and rod [1]; make up with distilled water until the bottom of the meniscus is on the line at eye level [1]; stopper and invert to mix [1] Examiner insight: Rinsings and mixing are separate creditworthy steps; leaving either out loses a mark.

4. (a) Concordant: 24.35, 24.45, 24.40 (24.55 excluded) [1]; mean = 24.40 cm³ [1] (b) c(acid) = (2.428 / 97.1) / 0.2500 = 0.1000 mol dm⁻³ [1]; n in 25.0 cm³ = 2.500 × 10⁻³ mol = n(NaOH) [1]; c(NaOH) = 2.500 × 10⁻³ / 0.02440 = 0.102 mol dm⁻³ [1] (c) Pipette: 0.04 / 25.0 × 100 = 0.16% [1]; titre: 0.10 / 24.40 × 100 = 0.41% [1] (d) Phenolphthalein or methyl orange (strong acid, strong base) [1] Examiner insight: Using the rough or a non-concordant titre in the mean usually costs the mark for the mean, so list the titres you used to show your choice.

5. (a) n(Li) = 0.0350 / 6.9 = 5.07 × 10⁻³ mol [1]; n(H₂) = 2.536 × 10⁻³ mol [1]; V = 2.536 × 10⁻³ × 24 000 = 60.9 cm³ [1] (b) A 100 cm³ gas syringe (or an inverted burette over water) [1] Examiner insight: Missing the 2 : 1 ratio doubles the answer, and the final answer must be in the unit asked for.

6. (a) Volatile reactants or products would evaporate [1]; the vertical condenser returns them to the flask so heating can continue [1] (b) Bulb level with the side arm [1]; water in at the bottom of the condenser [1] Examiner insight: “Stops it boiling dry” is too vague; say that vapour condenses and returns.

7. (a) Dissolve in the minimum hot water [1]; filter hot to remove insoluble impurities [1]; cool, then in ice, to crystallise [1]; filter under reduced pressure, wash with ice-cold water and dry [1] (b) 3.52 / 4.60 × 100 = 76.5% [1] (c) The crude solid melted lower and over a range, so it was impure [1]; the crystals melt sharply close to 122 °C, so they are much purer [1] Examiner insight: “Minimum” and “hot” are both needed for the first mark; excess solvent explains a low recovery.

8. (a) 4.2 / 8.4 = 0.50 [1]; 2.1 / 8.4 = 0.25 [1] (b) The sample probably contains A, plus at least one other substance [1] (c) Ink would dissolve and run [1]; spots below the solvent would dissolve into it [1] Examiner insight: Measure to the solvent front, not the top of the plate, or both Rf values are wrong.

9. Warm with NaOH(aq) [1]; gas turns damp red litmus blue, showing ammonium [1]; add barium nitrate solution: white precipitate shows sulfate [1]; add silver nitrate: cream precipitate [1]; soluble in concentrated but not dilute ammonia, showing bromide [1] Examiner insight: Barium chloride would add chloride before the halide test, so name barium nitrate when a halide test follows.

10. (a) 0.34 − (−0.25) = +0.59 V [1] (b) Copper in 1.00 mol dm⁻³ Cu²⁺(aq) and nickel in 1.00 mol dm⁻³ Ni²⁺(aq), at 298 K [1]; join the solutions with a salt bridge of potassium nitrate [1]; connect the electrodes to a high-resistance voltmeter [1] Examiner insight: The voltmeter must be high-resistance so almost no current flows; “a voltmeter” alone may not earn that mark.

11. (a) Each run makes the same fixed amount of iodine, so rate is proportional to 1/t [1] (b) Runs 1 to 2: [A] doubles, t halves: first order in A [1]; runs 2 to 3: [B] doubles, t halves: first order in B [1] (c) rate = k[A][B] [1] (d) Collect gas in a gas syringe [1]; record the volume at regular time intervals [1]; plot volume against time and draw a tangent at t = 0; its gradient is the initial rate [1] (e) A spreadsheet calculates 1/t and plots graphs [1] Examiner insight: State the change in each variable and its effect; a bare “first order” without the comparison may not gain credit.

12. (a) HNO₃: −log(0.0500) = 1.30 [1]; propanoic acid: [H⁺] = √(1.3 × 10⁻⁵ × 0.0500), pH = 3.09 [1]; KOH: [H⁺] = 1.00 × 10⁻¹⁴ / 0.0500, pH = 12.70 [1] (b) Rinse the probe with distilled water [1]; calibrate with buffer solutions of known pH [1] (c) The meter gives a more precise value, so close pH values can be told apart [1] Examiner insight: Treating propanoic acid as fully dissociated gives pH 1.30, which loses the mark; use the Ka expression for a weak acid.

Where marks are usually lost

• Control measures not linked to a named hazard.
• Rough or non-concordant titres in the mean.
• Missing the rinsing or mixing steps when making up a standard solution.
• Forgetting the 2 : 1 mole ratio in gas-volume questions.
• Placing the thermometer bulb in the liquid during distillation.
• Saying impurities raise the melting point.
• Using barium chloride before a halide test.
• Writing “voltmeter” without “high-resistance”.
• Treating a weak acid as fully dissociated in a pH calculation.

Next steps

• Revision notes
• Study guide
• Course hub for OCR A Level Chemistry A
• Printable H432 checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

OCR A Level Chemistry A (H432) specification, Version 3.1 (May 2026), for first assessment in 2017, published by OCR. Sections 1.2.1, 1.2.2 and 5g.