Reactions of calcium compounds.

This reaction shows the relationships between different calcium compounds.

Limewater is used to test for carbon dioxide, if carbon dioxide is bubbled through limewater it forms insoluble calcium carbonate. This turns the limewater cloudy.

When calcium carbonate is heated it undergoes thermal decomposition to form calcium oxide and carbon dioxide.

When water is added to calcum oxide a lot of heat is released. The mixture fizzes, steam is given off and the calcium oxide crumbles to a white powder of calcium hydroxide. If more water is added to the reactants, the calcium hydroxide dissolves to form a solution called limewater.

Word equations that you need to know: ​Using calcium compounds
 * calcium carbonate = calcium oxide + carbon dioxide
 * calcium oxide + water = calcium hydroxide
 * calcium hydroxide + carbon dioxide = calcium carbonate

Calcium carbonate, calcium oxide and calcium hydroxide can all be used to neutralise acidic compunds. Some soils are acidic. Farmers use calcium compounds to neutralise the acidity so their crops will grow better.