Carbonates (chemistry only) - AQA GCSE Chemistry Exam Questions

Practise 10 exam-style questions on Carbonates (chemistry only) for AQA GCSE Chemistry. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.

10 questions
1–6 marks each
Instant marking
No sign-up needed

10 questions, marked as you go

Sample questions with model answers

Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.

Question 1

2 marks

When any carbonate reacts with a dilute acid, the reaction between the carbonate ions and the hydrogen ions can be shown by one ionic equation.

Write this balanced ionic equation.

Model answer

CO₃²⁻ + 2H⁺ → H₂O + CO₂

Explanation

The metal ion and the acid's negative ion are spectator ions, so they are left out. A carbonate ion has a 2− charge, so it needs two H⁺ ions; the charges balance (zero on each side).

Mark scheme

1 mark
CO₃²⁻ + H⁺ → H₂O + CO₂
correct species; ignore state symbols
1 mark
balanced: CO₃²⁻ + 2H⁺ → H₂O + CO₂

Question 2

3 marks

Describe how to test a solid to show that it contains carbonate ions. Give the results you would expect.

Model answer

Add dilute hydrochloric acid to the solid. If it contains carbonate ions, it fizzes. Bubble the gas given off through limewater: the limewater turns milky, showing the gas is carbon dioxide.

Explanation

Fizzing on its own is not enough, because other substances (such as reactive metals) also fizz with acids. The limewater test confirms that the gas is carbon dioxide, which shows a carbonate was present.

Mark scheme

1 mark
add a dilute acid to the solid
allow any named dilute acid
1 mark
fizzing / effervescence / bubbles
1 mark
bubble the gas through limewater, which turns milky / cloudy
both limewater and milky / cloudy needed

Question 3

3 marks

Limescale forms inside kettles in hard water areas. Limescale is mainly calcium carbonate. When a descaler containing a dilute acid is added to the kettle, the limescale fizzes and disappears.

Explain why the limescale fizzes, and describe how you could show which gas is produced.

Model answer

The acid in the descaler reacts with the calcium carbonate to form a soluble calcium salt, water and carbon dioxide. The carbon dioxide gas causes the fizzing. To show the gas is carbon dioxide, bubble it through limewater: the limewater turns milky.

Explanation

This is the same reaction used to test for carbonate ions: acid plus carbonate gives carbon dioxide. The limescale disappears because the calcium salt formed dissolves in water.

Mark scheme

1 mark
the acid reacts with calcium carbonate
1 mark
carbon dioxide gas is produced
1 mark
bubble the gas through limewater, which turns milky / cloudy

Question 4

4 marks

An indigestion tablet has a mass of 1.25 g. It contains calcium carbonate. A student adds the tablet to excess dilute hydrochloric acid and collects 0.240 dm³ of carbon dioxide at room temperature and pressure.

CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)

Relative atomic masses (Ar): C = 12, O = 16, Ca = 40
The volume of one mole of any gas at room temperature and pressure is 24 dm³.

Calculate the percentage by mass of calcium carbonate in the tablet. Assume that only calcium carbonate produces gas.

Model answer

moles of CO₂ = 0.240 ÷ 24 = 0.0100 mol
1 mol CaCO₃ gives 1 mol CO₂, so moles of CaCO₃ = 0.0100 mol
Mr of CaCO₃ = 40 + 12 + (3 × 16) = 100
mass of CaCO₃ = 0.0100 × 100 = 1.00 g
percentage = (1.00 ÷ 1.25) × 100 = 80%

Explanation

Work backwards from the gas: volume ÷ 24 gives moles of carbon dioxide, which equals the moles of calcium carbonate. Convert to a mass and compare it with the mass of the whole tablet.

Mark scheme

1 mark
moles of CO₂ = 0.240 ÷ 24 = 0.0100 mol
1 mark
moles of CaCO₃ = 0.0100 mol
allow ecf; 1:1 ratio
1 mark
mass of CaCO₃ = 0.0100 × 100 = 1.00 g
allow ecf; Mr of CaCO₃ = 100
1 mark
percentage = 1.00 ÷ 1.25 × 100 = 80(%)
allow ecf; correct answer with no working scores 4 marks

Ready to try the rest? Every answer you write is marked against the mark scheme, so you can see exactly where the marks are.

AI Tutor Hints first, answers after you try

Hi! Stuck? Ask me for a hint and I’ll help you work it out. Once you’ve checked your answer I can explain exactly where the marks are.