Carbonates — AQA GCSE Chemistry
Test yourself on Carbonates with AQA GCSE practice questions.
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Carbonates explained
Metal carbonates contain the carbonate ion, CO₃²⁻.
Read the full explanation
When a carbonate reacts with a dilute acid, such as hydrochloric, sulfuric or nitric acid, a salt, water and carbon dioxide are produced. For example, calcium carbonate plus dilute hydrochloric acid gives calcium chloride, water and carbon dioxide: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). The carbon dioxide is seen as effervescence, and it turns limewater milky. The reaction is a neutralisation in which the carbonate ion accepts hydrogen ions, releasing carbon dioxide and water. Students should be able to name the salt formed from the acid used and the metal in the carbonate, and to describe a simple test-tube method for observing the gas.
Your focus
- Describe the reaction between a named carbonate and a dilute acid, including the products formed.
- Write a balanced equation for a carbonate–acid reaction.
- Explain how carbon dioxide production can be observed and tested in the laboratory.
Carbonates exam tips
Marking Points
- State that a carbonate reacts with a dilute acid to produce a salt, water and carbon dioxide.
- Identify carbon dioxide as the gas responsible for effervescence or bubbling during the reaction.
- Name the salt formed from the metal in the carbonate and the acid used, for example calcium chloride from calcium carbonate and hydrochloric acid.
- Write a balanced symbol equation for a named carbonate and dilute acid, including state symbols where required.
- Describe how the gas can be collected or tested, for example using limewater to confirm carbon dioxide.
- Explain that the carbonate ion reacts with hydrogen ions from the acid, releasing carbon dioxide and water.
Examiner Tips
- 💡Link the observation of bubbling to the production of carbon dioxide rather than to hydrogen or oxygen.
- 💡When asked to name a salt, identify the metal from the carbonate and the negative ion from the acid before writing the name.
- 💡Practise balancing equations for group 1 and group 2 carbonates with hydrochloric, sulfuric and nitric acids.
Common Mistakes
- Writing that carbon dioxide is the only product; the correction is that a salt and water are also formed.
- Naming the salt from the acid alone without considering the metal in the carbonate; the correction is to combine the metal ion with the acid's negative ion.
- Assuming all carbonates react in exactly the same ratio with every acid; the correction is to balance the equation for the specific carbonate and acid used.