Acids & CarbonatesOxford AQA IGCSE Chemistry: Revision notes
Section 1
What happens when a metal carbonate reacts with an acid?
Metal carbonates react with acids to produce three products: carbon dioxide gas, a salt, and water. This is a standard reaction type that appears across many metal carbonates, such as calcium carbonate, magnesium carbonate, copper carbonate and sodium carbonate.
General word equation: metal carbonate + acid -> salt + water + carbon dioxide
Section 2
Which salt is formed depends on the acid used
As with any acid reaction, the identity of the salt produced depends on which acid reacts with the carbonate:
- Hydrochloric acid produces chloride salts.
- Nitric acid produces nitrate salts.
- Sulfuric acid produces sulfate salts.
The metal in the salt comes from the metal carbonate used.
Calcium carbonate + hydrochloric acid gives calcium chloride, water and carbon dioxide.
Section 3
How can you tell the reaction is happening?
When a metal carbonate reacts with an acid, effervescence (fizzing/bubbling) is seen as carbon dioxide gas is released. This gas can be confirmed as carbon dioxide by bubbling it through limewater, which turns cloudy white in its presence - this is exactly how the reaction between carbonates and acids is used as a chemical test for carbonates.
When writing a word or symbol equation for a carbonate-acid reaction, always include all three products - a salt, water, AND carbon dioxide. Missing one of these loses marks even if the others are correct.
Section 4
How do you write a symbol equation for this reaction?
- Identify the metal carbonate and the acid.
- Work out the salt formed (metal from the carbonate, and chloride/nitrate/sulfate depending on the acid).
- Balance the equation so the number of each type of atom is equal on both sides.
- Add state symbols: (s) for the solid carbonate, (aq) for the acid, and (aq), (l), (g) for the salt, water and carbon dioxide respectively.
CaCO3(s) + 2HCl(aq) -> CaCl2(aq) + H2O(l) + CO2(g)
Must Know
- Metal carbonate + acid -> salt + water + carbon dioxide.
- The acid used determines the salt formed: hydrochloric = chloride, nitric = nitrate, sulfuric = sulfate.
- Effervescence (fizzing) is observed as carbon dioxide gas is released.
- The carbon dioxide produced can be confirmed by bubbling it through limewater, which turns cloudy white.
- A full equation for this reaction must always show three products: a salt, water, and carbon dioxide.
That's the notes covered.
Carry on to the next subtopic.