Explain — 3 marks
A student is cleaning a bathroom and notices limescale (calcium carbonate) deposits on the shower head. They decide to use a bottle of dilute hydrochloric acid cleaner to remove the limescale. The student observes vigorous fizzing as the acid reacts with the limescale.
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(a) Write the chemical equation for the reaction between hydrochloric acid and calcium carbonate.
[1 mark]
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(b) Explain why the student observes vigorous fizzing when the acid is applied to the limescale.
[1 mark]
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(c) Explain why dilute hydrochloric acid is more suitable for cleaning the shower head than concentrated hydrochloric acid, in terms of both safety and the rate of reaction.
[1 mark]
Show mark scheme
- (a) 2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂ (or correct equation with state symbols)
- (b) Carbon dioxide gas is produced/released during the reaction (fizzing is the escape of CO₂ gas bubbles)
- (c) Dilute acid is safer because it is less corrosive/less likely to cause burns to skin OR concentrated acid reacts too quickly/violently and is harder to control, whereas dilute acid reacts at a manageable rate
Suggest — 2 marks
A student is cleaning a bathroom and notices limescale deposits on the shower head. Limescale is mainly calcium carbonate. The student decides to use a bottle of white vinegar, which contains ethanoic acid, to remove the limescale.
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(a) Suggest why ethanoic acid in vinegar is suitable for removing limescale deposits.
[1 mark]
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(b) Suggest what type of substance would be produced when the ethanoic acid reacts with the calcium carbonate in the limescale.
[1 mark]
Show mark scheme
- (a) Acid reacts with (calcium) carbonate / acid dissolves limescale
- (a) Ethanoic acid is a weak acid so it is safe to use on bathroom surfaces
- (a) The reaction produces carbon dioxide gas which helps remove deposits
- (b) A salt (calcium ethanoate) would be produced
- (b) Water would be produced
- (b) Carbon dioxide gas would be produced
- (b) A solution / liquid would be produced
Define — 3 marks
A student is investigating the reaction between hydrochloric acid and calcium carbonate in a laboratory. The reaction produces a gas that causes limewater to turn cloudy. The student needs to understand the key chemical concepts involved in this acid reaction.
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(a) Define what is meant by an acid.
[1 mark]
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(b) Define what is meant by a base.
[1 mark]
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(c) Define what is meant by a salt in the context of acid-base reactions.
[1 mark]
Show mark scheme
- (a) A substance that produces hydrogen ions (H⁺ or H₃O⁺) when dissolved in water / donates protons
- (b) A substance that produces hydroxide ions (OH⁻) when dissolved in water / accepts protons / neutralises an acid
- (c) An ionic compound formed when an acid reacts with a base / produced when the hydrogen ions from an acid are replaced by metal ions (or ammonium ions)
Calculate — 2 marks
Copper sulfate is used in laboratories to test for the presence of water. It is prepared by reacting copper oxide powder with sulfuric acid. The equation for the reaction is: CuO + H₂SO₄ → CuSO₄ + H₂O. Relative formula masses: CuO = 80, CuSO₄ = 160.
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(a) Calculate the mass of copper sulfate produced when 4.0 g of copper oxide completely reacts with sulfuric acid.
[1 mark]
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(b) Calculate the mass of copper oxide needed to produce 20 g of copper sulfate.
[1 mark]
Show mark scheme
Explain — 3 marks
A student adds magnesium ribbon to dilute hydrochloric acid in a test tube. The mixture fizzes vigorously and the magnesium disappears.
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(a) Explain why the mixture fizzes.
[1 mark]
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(b) Explain what happens to the magnesium and name the salt formed in this reaction.
[2 marks]
Show mark scheme
- (a) hydrogen gas is produced / gas is given off
- (b) the magnesium reacts with the acid / the magnesium is used up
- (b) magnesium chloride
GCSE Perfect