AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Carbonates: Carbonates react with dilute acids to form carbon dioxide gas.
Metal carbonates contain the carbonate ion, CO₃²⁻.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 1 of 2
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Metal carbonates contain the carbonate ion, CO₃²⁻. 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.
What earns the marks
- 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.
Common mistakes and how to put them right
Writing that carbon dioxide is the only product.
Put it right: A salt and water are also formed.
Naming the salt from the acid alone without considering the metal in the carbonate.
Put it right: Combine the metal ion with the acid's negative ion.
Assuming all carbonates react in exactly the same ratio with every acid.
Put it right: Balance the equation for the specific carbonate and acid used.
Exam 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.
Try the lesson
The start of the Carbonates: Carbonates react with dilute acids to form carbon dioxide gas. lesson, made from checked teaching notes for this specification point.
Have a go first
Which gas is formed when a carbonate reacts with a dilute acid?
Listen
Metal carbonates contain the carbonate ion, CO₃²⁻. 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. A strong answer earns marks for these 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. A common slip: Writing that carbon dioxide is the only product. Instead, a salt and water are also formed. Exam tip: Link the observation of bubbling to the production of carbon dioxide rather than to hydrogen or oxygen.
See it
Key words
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Acid–carbonate reactions
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Gas production and observation
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Salt formation
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Balanced chemical equations
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See every definition
- Acid–carbonate reactions
- Reactions in which a carbonate reacts with a dilute acid to produce a salt, water and carbon dioxide.
- Gas production and observation
- Carbon dioxide is seen as effervescence, and it turns limewater milky.
- Salt formation
- The salt is named from the metal in the carbonate and the acid used.
- Balanced chemical equations
- A balanced symbol equation for a named carbonate and dilute acid, including state symbols where required.
Label the diagram
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