OCR GCSE Chemistry A: Types of chemical reactions (J248) – 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.

Every question below is on sub-topic C3.3 Types of chemical reactions of the OCR GCSE (9–1) Chemistry A (Gateway Science) J248 specification (Version 4.0, August 2026). Together the questions test outcomes C3.3a–C3.3k, mathematical learning outcome CM3.3i, and the PAG C6 and PAG C7 practical suggestions. Questions on C3.3b, C3.3g, C3.3i and C3.3j are labelled Higher Tier only; the rest suit both tiers.

Before you start, work through the Types of chemical reactions study guide or the Types of chemical reactions revision notes. The OCR GCSE Chemistry hub and the J248 checklist place C3.3 in the whole course; a free 10-minute diagnostic points you to weak areas.

Questions

1. A mixture of zinc powder and copper(II) oxide is heated. A glow spreads through the mixture and pink-brown copper forms: Zn + CuO → ZnO + Cu

(a) State which substance is oxidised. Give a reason. [2] (b) Identify the reducing agent. [1]

2. Silicon can be made in the laboratory by heating dry sand (silicon dioxide) with magnesium powder: SiO₂ + 2Mg → Si + 2MgO

Explain, in terms of oxygen, which substance is oxidised and which is reduced, and identify the oxidising agent. [3]

3. (Higher Tier only) Aluminium powder reacts with copper(II) sulfate solution. The ionic equation is: 2Al + 3Cu²⁺ → 2Al³⁺ + 3Cu

(a) Write the two half equations for this reaction. [2] (b) Explain, in terms of electrons, which species is oxidised. [1] (c) State which species is the oxidising agent. [1]

4. Acid and alkali solutions both contain ions.

(a) Give the name of the ion every acid produces in water. [1] (b) Write an equation to show the ions formed when nitric acid, HNO₃, dissolves in water. [1] (c) A student writes: “In hydrochloric acid, the hydrogen ions stay joined to the chlorine.” Explain why the student is wrong. [1] (d) Name the ion present in every alkali solution. [1]

5. Write a balanced equation for each reaction.

(a) Potassium carbonate with hydrochloric acid. [2] (b) Zinc with hydrochloric acid, forming zinc chloride. [2] (c) Copper(II) carbonate with nitric acid, forming copper(II) nitrate, Cu(NO₃)₂. [2]

6. Barium hydroxide solution is neutralised by dilute nitric acid.

(a) Describe what is meant by neutralisation. [1] (b) Name the salt formed. [1] (c) Write the ionic equation for this neutralisation, with state symbols. [2] (d) Explain why the barium ions and nitrate ions are not shown in the ionic equation. [1]

7. Describe how to make a pure, dry sample of copper(II) nitrate crystals from copper(II) carbonate powder and dilute nitric acid. Explain how you would know that all the acid had reacted. [6]

8. (Higher Tier only) A technician has four bottles of acid.

Bottle	Acid	Concentration (mol/dm³)
P	hydrochloric acid	2.0
Q	hydrochloric acid	0.05
R	ethanoic acid	2.0
S	ethanoic acid	0.05

(a) Identify the bottle that contains a dilute, strong acid. [1] (b) Identify the bottle that contains a concentrated, weak acid. [1] (c) Explain what makes an acid strong rather than weak. [2] (d) In a simple model of a weak acid solution, 6 molecules out of every 500 are ionised. Calculate the percentage ionised. [1] (e) Bottle T holds 0.25 mol of nitric acid in 125 cm³ of solution. Calculate its concentration in mol/dm³, and state which bottle in the table has the same concentration. [2]

9. (Higher Tier only)

(a) A solution changes from pH 13 to pH 10. Describe how the hydrogen ion concentration changes, and by what factor. [2] (b) An acid solution changes from pH 3 to pH 5 when water is added. By what factor has the hydrogen ion concentration decreased? [1] (c) 10 cm³ of a strong acid with pH 1 is diluted with water to a total volume of 100 cm³. Predict the new pH. Show your reasoning. [2]

10. (Higher Tier only) A student adds hydrochloric acid from a burette to 25.0 cm³ of sodium hydroxide solution, recording the pH with a probe.

Acid added (cm³)	0	10	20	24	24.9	25.0	25.1	26	30	50
pH	13	13	12	11	10	7	4	3	2	1

(a) Describe the shape of the pH data as the acid is run in. [3] (b) State the volume of acid that exactly neutralises the alkali. [1] (c) State the pH at that point and what it shows. [1] (d) Explain, in terms of ions, why the pH changes only slowly between 0 and 20 cm³. [1]

11. A student tests four unknown solutions, W to Z, with universal indicator paper.

Solution	W	X	Y	Z
Colour	yellow	red	purple	green

(a) Put the solutions in order from most acidic to most alkaline, and identify the neutral solution. [2] (b) Describe how to use a pH probe to measure the pH of solution W. [3] (c) Give two advantages of a pH probe over universal indicator paper. [2]

Answers

1. (a) Zinc is oxidised [1] because it gains oxygen, forming zinc oxide [1]. (b) Zinc (Zn) [1] Examiner insight: In (a), the reason needs the word “gains” and the link to oxygen; just saying “it forms zinc oxide” leaves out why that counts as oxidation.

2. Magnesium gains oxygen (forms MgO), so magnesium is oxidised [1]. Silicon dioxide loses oxygen (forms Si), so silicon dioxide is reduced [1]. The oxidising agent is silicon dioxide [1]. Examiner insight: Naming “silicon” as the substance reduced is a common slip: silicon is the product, while silicon dioxide is the substance that lost oxygen.

3. (a) Al → Al³⁺ + 3e⁻ [1]; Cu²⁺ + 2e⁻ → Cu [1] (b) Aluminium (atoms) is oxidised because each atom loses electrons (three) [1]. (c) Copper(II) ions, Cu²⁺ [1] Examiner insight: Half equations are usually written for one atom or ion, as here; check each balances for charge, because a half equation with electrons on the wrong side shows the opposite process.

4. (a) Hydrogen ion, H⁺ [1] (b) HNO₃ → H⁺ + NO₃⁻ [1] (c) In water the acid splits into ions, so the H⁺ ions are separate and free to move in the solution, not bonded to chlorine [1]. (d) Hydroxide ion, OH⁻ [1] Examiner insight: “Hydrogen” alone in (a) is ambiguous; give the ion and its charge so it cannot be read as hydrogen gas.

5. (a) Products potassium chloride, water and carbon dioxide [1]; K₂CO₃ + 2HCl → 2KCl + H₂O + CO₂ [1] (b) Products zinc chloride and hydrogen [1]; Zn + 2HCl → ZnCl₂ + H₂ [1] (c) Products copper(II) nitrate, water and carbon dioxide [1]; CuCO₃ + 2HNO₃ → Cu(NO₃)₂ + H₂O + CO₂ [1] Examiner insight: Count atoms on both sides before moving on; the balancing mark depends on every element matching, including oxygen in the carbonate.

6. (a) An acid reacts with an alkali (or base) to form a salt and water [1]. (b) Barium nitrate [1] (c) H⁺(aq) + OH⁻(aq) → H₂O(l) [1] correct state symbols [1] (d) They are spectator ions: they are in the solution before and after the reaction and do not change [1]. Examiner insight: When a question asks for state symbols, leaving them out loses credit even if every formula is right.

7.

• Warm the dilute nitric acid in a beaker [1].
• Add copper(II) carbonate a little at a time, stirring [1].
• Keep adding until fizzing stops and some solid stays undissolved: the acid has all reacted [1].
• Filter to remove the excess copper(II) carbonate [1].
• Warm the filtrate in an evaporating basin until crystals start to appear at the edge, then set it aside to cool and crystallise [1].
• Filter off or pick out the crystals and dry them between filter paper or in a warm oven [1].

Examiner insight: A six-mark method needs steps in a workable order; describing filtration before the excess solid has been added, or heating the solution to dryness, weakens the answer.

8. (a) Q [1] (b) R [1] (c) A strong acid is completely ionised in water [1]; a weak acid is only partially ionised [1]. (d) 6 ÷ 500 × 100 = 1.2% [1] (e) 125 cm³ = 0.125 dm³; 0.25 ÷ 0.125 = 2.0 mol/dm³ [1]; same as P (and R) [1] Examiner insight: In (c), “strong means more concentrated” confuses the two pairs of words and scores nothing; the answer must refer to ionisation.

9. (a) The H⁺ concentration increases [1] by a factor of 1000 (10 × 10 × 10) [1]. (b) 100 [1] (c) Volume increases 10 times, so H⁺ concentration falls by a factor of 10 [1]; pH rises by 1, to pH 2 [1]. Examiner insight: In (a), stating the factor without the direction (increase) answers only half the question; check whether the pH went up or down first.

10. (a) The pH starts high, at 13 [1], and falls slowly at first [1]; near 25 cm³ it drops steeply through 7, then levels off at a low pH (about 1) [1]. (b) 25.0 cm³ [1] (c) pH 7: the solution is neutral [1]. (d) There is still a large excess of OH⁻ ions, so neutralising some of them hardly changes the pH [1]. Examiner insight: Describing a curve gains credit for using the data: quote the starting pH, the volume at the steep drop and the final level rather than “it goes down”.

11. (a) X, W, Z, Y (most acidic to most alkaline) [1]; Z is neutral [1]. (b) Calibrate the probe using buffer solutions of known pH [1]. Rinse the probe with distilled water [1]. Put the probe into solution W and read the pH on the display when it is steady [1]. (c) Any two: more precise reading [1]; not affected by the colour of the solution [1]; no subjective colour matching; can record pH continuously. Examiner insight: “More accurate” on its own is vague; say what makes it better, such as a reading to a decimal place or no colour judgement.

Where marks are usually lost

• Naming the product (copper, silicon) instead of the oxide as the substance reduced.
• Calling the oxidising agent “oxidised” when it is reduced.
• (Higher Tier only) Showing electrons as gained in a half equation for an oxidation.
• Missing water or carbon dioxide from an acid + carbonate equation.
• Forgetting brackets in formulae such as Cu(NO₃)₂.
• Missing (aq) and (l) in an ionic equation that asks for state symbols.
• Describing salt preparation without saying the solid is added in excess.
• (Higher Tier only) Using “strong” to mean “concentrated”.
• (Higher Tier only) Treating a pH change of 3 as a factor of 3 rather than 1000.
• Not converting cm³ to dm³ in a concentration calculation.

Next steps

• Recap with the Types of chemical reactions revision notes.
• Go back to the Types of chemical reactions study guide for the outcomes that caught you out.
• Tick off C3.3 on the J248 checklist and pick your next topic from the OCR GCSE Chemistry hub.
• Try one of the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

OCR GCSE (9–1) Chemistry A (Gateway Science) J248 specification, Version 4.0 (August 2026), for first assessment in 2018, published by OCR. Sub-topic C3.3 Types of chemical reactions, learning outcomes C3.3a–C3.3k, mathematical learning outcome CM3.3i and practical suggestions (PAG C6, PAG C7).