Limestone is mainly calcium carbonate, CaCO3, which when heated breaks down to form calcium oxide and carbon dioxide. Calcium oxide reacts with water to produce calcium hydroxide. Limestone and its products have many uses, including being used to make cement, mortar and concrete.
Calcium carbonate breaks down when heated strongly. This reaction is called thermal decomposition. Here are the equations for the thermal decomposition of calcium carbonate:
calcium carbonatecalcium oxide + carbon dioxide
CaCO3CaO + CO2
Other metal carbonates decompose in the same way, including:
- sodium carbonate
- magnesium carbonate
- copper carbonate
For example, here are the equations for the thermal decomposition of copper carbonate:
copper carbonate copper oxide + carbon dioxide
CuCO3CuO + CO2
Metals high up in the reactivity series (such as sodium, calcium and magnesium) have carbonates that need a lot of energy to decompose them. Indeed, not all the carbonates of group 1 metals decompose at the temperatures reached by a Bunsen burner.
Metals low down in the reactivity series, such as copper, have carbonates that are easily decomposed. This is why copper carbonate is often used at school to show thermal decomposition. It is easily decomposed and its colour change, from green copper carbonate to black copper oxide, is easy to see.
Products from calcium carbonate
For your exam, you need to know how calcium hydroxide is obtained from calcium carbonate.
Making calcium oxide
If calcium carbonate is heated strongly, it breaks down to form calcium oxide and carbon dioxide. Calcium oxide is yellow when hot, but white when cold.
Here are the equations for this reaction:
calcium carbonate calcium oxide + carbon dioxide
CaCO3 CaO + CO2
This is a thermal decomposition…