O Level Chemistry 5070 · Topic 7

Acids, bases and salts: past paper questions

144 real questionsasked in 9 of the last 10 exam series2019–2025usually: State, Describe, Name, Explain, Identify

Real questions on acids, bases and salts

The newest 20 of 71 written questions, plus 73 multiple-choice. Open one to see it on the real paper.

5070/21 · May/June 2025 · Q4c(ii)[1]
Water is added to the reaction mixture to make an aqueous solution. A few drops of litmus are then added. The litmus changes colour to blue. Suggest the name of the ion present in the aqueous solution responsible for the colour change.
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5070/21 · May/June 2025 · Q6d(i)[2]
The temperature of the equilibrium mixture is increased. State and explain what happens to the acidity of the equilibrium mixture. statement explanation
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5070/21 · May/June 2025 · Q6d(ii)[2]
HCl (aq) is a strong acid and HOCl (aq) is a weak acid. Describe the difference between a strong acid and a weak acid.
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5070/22 · May/June 2025 · Q4c(i)[1]
State the name of the compound Ca(CH 3 COO) 2 .
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5070/42 · May/June 2025 · Q3a(i)[2]
Describe how to do a flame test on a solid.
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5070/42 · May/June 2025 · Q3a(ii)[1]
The student observes a blue-green colour in the flame. Identify the cation present in A.
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5070/42 · May/June 2025 · Q3b(i)[5]
Describe the observations the student makes. Describe the chemical test and the positive result used to identify the gas formed. observations test
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5070/42 · May/June 2025 · Q3c[4]
Explain how the student uses aqueous ammonia to confirm the metal ion present in C. Include the observations you expect.
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5070/42 · May/June 2025 · Q3d[1]
The student does tests on B. The results are shown in Table 3.1. Table 3.1 test observation adds dilute nitric acid and aqueous barium nitrate colourless solution formed adds dilute nitric acid and aqueous silver nitrate cream precipitate formed adds aqueous sodium hydroxide and aluminium foil then warms the mixture co...
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5070/21 · October/November 2024 · Q4d(i)[1]
Name product X.
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5070/21 · October/November 2024 · Q7a(ii)[2]
Propanoic acid is a weak acid. CH 3 CH 2 COOH + H 2 O Explain how this equation shows that: • CH 3 CH 2 COOH is an acid by referring to proton transfer • CH 3 CH 2 COO – + H 3 O + CH 3 CH 2 COOH is a weak acid.
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5070/22 · October/November 2024 · Q1a(v)[1]
an atom that forms a stable ion with a charge of 2–.
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5070/42 · October/November 2024 · Q1a[1]
The student makes aqueous copper( II ) sulfate by reacting a dilute acid with excess copper( II ) oxide. Name the acid.
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5070/21 · May/June 2024 · Q3d[2]
One way to measure the pH of aqueous ammonium nitrite is to use a pH meter. Describe one other way to measure the pH of aqueous ammonium nitrite.
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5070/21 · May/June 2024 · Q8d[2]
State the name and formula of compound D. name formula
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5070/21 · May/June 2024 · Q8e[2]
State the name of gas E and of gas F. E F
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5070/22 · May/June 2024 · Q3d(i)[1]
State which ion is responsible for this pH value.
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5070/22 · May/June 2024 · Q3d(ii)[2]
A pH meter is used to measure the pH of an aqueous solution. Describe one other way to measure the pH of an aqueous solution.
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5070/21 · October/November 2023 · Q6c(i)[1]
Name this salt.
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5070/21 · October/November 2023 · Q7c(i)[1]
Define the term weak in the phrase weak acid.
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What examiners said

The name of the salt was well derived. Common incorrect responses included ammonia nitrate, ammonium and nitrogen hydroxide. A small number omitted the question.
— Examiner report, October/November 2023, 5070/21 Q6(c)(i) (Cambridge)

The term weak was well known. Incorrect responses included: dissolved instead of dissociated; has few H+ or has a high pH.
— Examiner report, October/November 2023, 5070/21 Q7(c)(i) (Cambridge)

The ion was quite well known. OH− was a popular response as was the neutralisation equation H+ + OH− H2O.
— Examiner report, October/November 2023, 5070/21 Q7(c)(ii) (Cambridge)

Practise this topic

Answer these questions online and get each one marked against the official mark scheme, with what you missed and how to fix it.

Practise acids, bases and salts

In the syllabus

7.1 The characteristic properties of acids and bases

State that aqueous solutions of acids contain H+ ions and aqueous solutions of alkalis contain OH – ions
Define acids as proton donors and bases as proton acceptors
State that bases are oxides or hydroxides of metals and that alkalis are soluble bases
Describe the characteristic properties of acids in terms of their reactions with: (a) metals (b) bases (c) carbonates
Describe the characteristic properties of bases in terms of their reactions with: (a) acids (b) ammonium salts
State that a neutralisation reaction occurs between an acid and a base
Describe the neutralisation reaction between an acid and an alkali to produce water, H+(aq) + OH−(aq) → H2O(l )
Describe acids and alkalis in terms of their effects on: (a) litmus (b) thymolphthalein (c) methyl orange
Define a strong acid as an acid that is completely dissociated in aqueous solution and a weak acid as an acid that is partially dissociated in aqueous solution
State examples of strong acids, including hydrochloric acid, nitric acid and sulfuric acid and construct the symbol equations to show their complete dissociation, e.g. HCl(aq) → H+(aq) + Cl – (aq)
State examples of weak acids, including carboxylic acids and construct the symbol equations to show their partial dissociation, e.g. for ethanoic acid, CH3COOH(aq) ⇌ H+(aq) + CH3COO – (aq)
Describe how to compare hydrogen ion concentration, neutrality, relative acidity and relative alkalinity in terms of colour and pH using universal indicator paper

7.2 Oxides

Describe amphoteric oxides as oxides that react with acids and bases to produce a salt and water
Classify oxides as acidic, including SO2 and CO2, basic, including CuO and CaO, or amphoteric, limited to Al 2O3 and ZnO, related to metallic and non-metallic character

7.3 Preparation of salts

Describe the preparation, separation and purification of soluble salts by reaction of an acid with: (a) an alkali by titration (b) excess metal (c) excess insoluble base (d) excess insoluble carbonate
Describe the preparation of insoluble salts by precipitation
Describe the general solubility rule for salts: (a) sodium, potassium and ammonium salts are soluble (b) nitrates are soluble (c) chlorides are soluble, except lead and silver (d) sulfates are soluble, except barium, calcium and lead (e) carbonates are insoluble, except sodium, potassium and ammonium (f) hydroxides are insoluble, except sodium, potassium, ammonium and calcium (partially)
Define a hydrated substance as a substance that is chemically combined with water and an anhydrous substance as a substance containing no water
Define the term water of crystallisation as the water molecules present in hydrated crystals, including CuSO4•5H2O and CoCl 2•6H2O

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