AQA GCSE Chemistry 8462: Chemical changes – 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 4.4 Chemical changes (4.4.1.1 to 4.4.3.5) of the AQA GCSE Chemistry (8462) specification, for teaching from September 2016 and exams from June 2018 onwards. The topic is assessed on Paper 1, set at Foundation and Higher Tier. Question 4 and the parts marked below test content the specification marks (HT only) and are labelled Higher tier only. Questions 6, 8 and 10 are based on required practicals 1, 2 and 3.

Learn the content first in the Chemical changes study guide and the revision notes. The course hub is AQA GCSE Chemistry, and the printable checklist lists every point. For more mole calculations, try the Quantitative chemistry practice questions.

Relative atomic masses: H = 1, N = 14, O = 16, Na = 23.

Questions

1. Lead is extracted by heating lead oxide with carbon: 2PbO + C → 2Pb + CO₂ Identify the substance that is oxidised and the substance that is reduced. Give a reason for each in terms of oxygen. [2]

2. A student adds four metals to water and to dilute hydrochloric acid at room temperature.

Metal	Water	Dilute hydrochloric acid
W	Fizzes vigorously and melts	Not tested
X	No visible reaction	Steady fizzing
Y	No reaction	No reaction
Z	A few bubbles slowly	Vigorous fizzing

(a) Put the metals in order of reactivity, most reactive first. [2] (b) Which metal could be copper? [1]

3. Explain why potassium reacts more vigorously with water than magnesium does. [2]

4. (Higher tier only) Zinc powder is added to blue copper sulfate solution. The solution fades and a brown solid forms.

(a) Write the ionic equation for the reaction. [1] (b) Write the two half equations. [2] (c) Identify the species that is oxidised. Explain your answer. [1]

5. This question is about salts.

(a) Name the salt made when zinc oxide reacts with nitric acid. [1] (b) Aluminium ions are Al³⁺ and sulfate ions are SO₄²⁻. Give the formula of aluminium sulfate. [1] (c) Name all the products when calcium carbonate reacts with hydrochloric acid. [2]

6. Describe how to make a pure, dry sample of zinc sulfate crystals from zinc carbonate and dilute sulfuric acid. [6]

7. This question is about acids.

(a) (Higher tier only) The pH of a solution falls from 6 to 2. Calculate the factor by which the hydrogen ion concentration increases. [2] (b) (Higher tier only) A bottle is labelled “dilute nitric acid”; another is labelled “concentrated ethanoic acid”. Explain what “dilute” and “weak” mean for these acids. [2] (c) Write the ionic equation for the reaction between an acid and an alkali. [1]

8. A student titrates 25.0 cm³ of nitric acid with 0.200 mol/dm³ sodium hydroxide solution. HNO₃ + NaOH → NaNO₃ + H₂O

Titration	Rough	1	2	3
Titre / cm³	24.10	23.70	23.80	23.75

(a) Describe how the student should carry out the titration to find the reacting volume accurately. [4] (b) Calculate the mean titre using the three accurate results. [1] (c) (Higher tier only) Calculate the concentration of the nitric acid in mol/dm³. [3] (d) (Higher tier only) Calculate the concentration of the nitric acid in g/dm³. Give your answer to 3 significant figures. [1]

9. This question is about electrolysis.

(a) Name the products at the cathode and at the anode when molten calcium bromide is electrolysed with inert electrodes. [2] (b) Explain why solid calcium bromide cannot be electrolysed. [1] (c) Aluminium is made by electrolysing aluminium oxide dissolved in molten cryolite, using carbon anodes. Explain why a mixture is used, and why the anodes must be replaced regularly. [4] (d) (Higher tier only) Write the half equation for the formation of aluminium. [1]

10. A student electrolyses aqueous solutions using inert electrodes.

(a) Predict the product at each electrode for sodium bromide solution and for copper sulfate solution. [4] (b) Explain why sodium is not produced from sodium bromide solution. [1] (c) (Higher tier only) Write the half equation for the reaction at the anode with sodium bromide solution. [1]

11. Zinc can be extracted by heating zinc oxide with carbon: ZnO + C → Zn + CO

(a) Identify what is oxidised and what is reduced in this reaction, in terms of oxygen. [2] (b) Explain why carbon can be used to extract zinc but not magnesium. [2] (c) (Higher tier only) In the laboratory, molten zinc chloride is electrolysed. Write the half equation at the cathode and state whether this is oxidation or reduction. [2] (d) (Higher tier only) Zinc reacts with dilute sulfuric acid: Zn + 2H⁺ → Zn²⁺ + H₂. Explain why this is a redox reaction. [2]

Answers

1. Carbon is oxidised because it gains oxygen (to form CO₂) [1]. Lead oxide is reduced because it loses oxygen (to form lead) [1]. Examiner insight: Naming “lead” as reduced is not credited; the substance reduced is lead oxide, the one that loses the oxygen.

2. (a) W most reactive and Y least [1]; Z above X: W, Z, X, Y [1] (b) Y [1] Examiner insight: Placing X above Y needs the acid column, because neither reacts visibly with water; using one column alone cannot give the full order.

3. Potassium atoms form positive ions more easily than magnesium atoms [1], so potassium is higher in the reactivity series and reacts faster [1]. Examiner insight: “Potassium is more reactive” repeats the question; the first mark needs the tendency to form positive ions.

4. (a) Zn + Cu²⁺ → Zn²⁺ + Cu [1] (b) Zn → Zn²⁺ + 2e⁻ [1]; Cu²⁺ + 2e⁻ → Cu [1] (c) Zinc (atoms) is oxidised because it loses electrons [1]. Examiner insight: Including sulfate ions in (a) loses the mark, because an ionic equation must leave out spectator ions.

5. (a) Zinc nitrate [1] (b) Al₂(SO₄)₃ [1] (c) Calcium chloride [1]; water and carbon dioxide [1] Examiner insight: In (c), the second mark needs both water and carbon dioxide; missing either loses it.

6. Any six from: warm the dilute sulfuric acid in a beaker using a Bunsen burner [1]; add zinc carbonate a little at a time, stirring [1]; continue until fizzing stops and solid remains, so the acid is all used up [1]; filter to remove the excess zinc carbonate [1]; heat the filtrate in an evaporating basin on a water bath or electric heater to evaporate some water [1]; leave to cool so crystals form, then filter them off and dry them between filter paper [1]. Examiner insight: A six-mark “describe” is marked by levels, so the steps must be in a logical order; a method that evaporates to dryness or skips filtering the excess cannot reach the top level.

7. (a) 6 − 2 = 4 pH units [1]; 10⁴ = 10 000 times [1] (b) Dilute means there is a small amount of acid in a given volume of solution [1]. Weak means the acid is only partially ionised in water, as ethanoic acid is [1]. (c) H⁺ + OH⁻ → H₂O [1] Examiner insight: In (a), answering “4 times” or “40 times” scores zero; each unit is a factor of 10, so the method mark needs 10 raised to the power 4.

8. (a) Use a pipette to put 25.0 cm³ of nitric acid in a conical flask with a few drops of indicator [1]; add sodium hydroxide from a burette while swirling the flask [1]; add dropwise near the end point and stop when the indicator changes colour [1]; repeat until results are concordant (close together) [1]. (b) (23.70 + 23.80 + 23.75) ÷ 3 = 23.75 cm³ [1] (c) Moles NaOH = 0.200 × 23.75 ÷ 1000 = 0.00475 mol [1]; ratio 1 : 1, so moles HNO₃ = 0.00475 mol [1]; concentration = 0.00475 ÷ 0.0250 = 0.190 mol/dm³ [1] (d) 0.190 × 63 = 11.97 = 12.0 g/dm³ [1] Examiner insight: Including the rough titre in the mean loses the mark in (b); the wrong mean can still be carried forward into (c) and (d).

9. (a) Calcium at the cathode [1]; bromine at the anode [1] (b) In the solid the ions are fixed in place and cannot move to the electrodes [1]. (c) The mixture melts at a lower temperature than aluminium oxide alone [1], so less energy is needed and costs are lower [1]. Oxygen forms at the carbon anodes and reacts with the carbon to make carbon dioxide [1], so the anodes wear away [1]. (d) Al³⁺ + 3e⁻ → Al [1] Examiner insight: “Electrons cannot move in the solid” earns nothing in (b); conduction in electrolysis is by moving ions.

10. (a) Sodium bromide: hydrogen at the cathode [1], bromine at the anode [1]. Copper sulfate: copper at the cathode [1], oxygen at the anode [1]. (b) Sodium is more reactive than hydrogen, so hydrogen is produced instead [1]. (c) 2Br⁻ → Br₂ + 2e⁻ [1] Examiner insight: Each electrode product is a separate mark, so a correct cathode prediction still scores even if the anode product is wrong.

11. (a) Carbon is oxidised because it gains oxygen [1]; zinc oxide is reduced because it loses oxygen [1]. (b) Zinc is less reactive than carbon, so carbon can remove the oxygen from zinc oxide [1]; magnesium is more reactive than carbon, so carbon cannot reduce magnesium oxide and electrolysis is needed [1]. (c) Zn²⁺ + 2e⁻ → Zn [1]; reduction, because the zinc ions gain electrons [1] (d) Zinc atoms lose electrons, so zinc is oxidised [1]; hydrogen ions gain electrons, so they are reduced [1]. Examiner insight: In (d), each mark needs the species and the electron transfer together; “zinc is oxidised” without the electron reason does not score.

Where marks are usually lost

• Naming the metal instead of the metal oxide as the substance reduced.
• Ordering metals from one set of results when a second set is needed to separate two of them.
• (Higher tier only) Leaving spectator ions in an ionic equation.
• Writing salt formulae without brackets, e.g. Al2SO43 instead of Al₂(SO₄)₃.
• In required practical 1, forgetting to add the solid in excess or to filter off the excess.
• Using the rough titre when calculating the mean.
• (Higher tier only) Confusing weak with dilute.
• Saying electrons, rather than ions, move through an electrolyte.
• Predicting the metal at the cathode for every aqueous solution.
• (Higher tier only) Putting electrons on the wrong side of a half equation.

Next steps

• Chemical changes revision notes
• Chemical changes study guide
• AQA GCSE Chemistry course hub
• Printable AQA GCSE Chemistry checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

AQA GCSE Chemistry (8462) specification, Version 1.1 (October 2019), for teaching from September 2016 and exams from June 2018 onwards (AQA), section 4.4 Chemical changes.