The Acid-Carbonate Reaction
How can we test for acids and carbonates?
- Carbonates all contain the carbonate ion, CO32–
- If we add an acid to a carbonate ion we see fizzing
- This is because the gas produced is CO2
- We can test for this gas by bubbling it through limewater. This then forms a white precipitate of calcium carbonate
CO32– (aq) + 2H+ (aq) → CO2 (g) + H2O (l)
CO2 (g) + Ca(OH)2 (aq) → CaCO3(s) + H2O (l)
Diagram showing the chemical test identifying acids and carbonates
Limewater turns milky in the presence of CO2 caused by the formation of insoluble calcium carbonate
Examiner Tip
You’ll need to connect the test tube of the suspected ion to the test tube of limewater quickly so none of the CO2 gas escapes.
Stating that carbon dioxide is formed is not actually an observation. Your observation in this reaction should be fizzing.
