Chemical Changes: Metal Carbonates
Chemical Changes: Metal Carbonates
Properties and Stability
- Metal carbonates are compounds that contain a metal, carbon and oxygen.
- These compounds are generally stable, however they can decompose when exposed to heat.
Thermal Decomposition
- Thermal decomposition is a chemical process where a substance breaks down into simpler substances when heated.
- Metal carbonates decompose to form a metal oxide and carbon dioxide gas when heated.
- For example, copper carbonate decomposes into copper oxide and carbon dioxide: CuCO3 → CuO + CO2
The Carbonate Test
- The carbonate test identifies the presence of carbonate ions within a substance.
- This involves adding an acid to the suspected carbonate and observing if carbon dioxide gas is produced, often visible through effervescence or fizzing.
- Carbon dioxide will turn limewater from clear to milky, confirming its presence.
Reactions with Acids
- Metal carbonates also react with acids to produce a salt, water and carbon dioxide.
- This can be represented in the general equation: Metal carbonate + Acid → Salt + Water + Carbon dioxide
- For instance, calcium carbonate reacts with hydrochloric acid to produce calcium chloride, water and carbon dioxide: CaCO3 + 2HCl → CaCl2 + H2O + CO2
Carbonate and Bicarbonate
- A related group of compounds are metal bicarbonates, also known as hydrogen carbonates.
- These compounds also react with acids to produce a salt, water and carbon dioxide, and decompose when heated.
Environmental Impact
- Carbon dioxide is a greenhouse gas that contributes to global warming.
- Whilst naturally occurring, the volume of carbon dioxide in the atmosphere is disproportionately increased by human activities, such as by the thermal decomposition of metal carbonates.
- Consequently, the use and disposal of metal carbonates should be managed to minimise environmental impact.