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 VISUAL CHEMISTRY

GROUP I : THE ALKALI EARTH METALS : COMPOUNDS

.1. Oxides

The metal oxides can be formed by heating the metal in a supply of air. They can also be produced by heating the metal hydroxide, metal nitrate or metal carbonate. The example below shows the decomposition of magnesium hydroxide on heating.
 

Mg(OH)2 MgO + H2O

When calcium carbonate (limestone) is roasted, calcium oxide is produced and carbon dioxide gas is liberated.

CaCO3 CaO  + CO2­

When water is added to the calcium oxide (quicklime), calcium hydroxide (lime water) is produced.

CaO + H2O  Ca(OH)2↓

2. Hydroxides

The metal hydroxide is produced by adding an alkali to a solution of the metal salt. Barium hydroxide is soluble on water. Strontium hydroxide is slightly soluble in water. Calcium and magnesium hydroxides are insoluble in water and form white precipitates.

MgCl2 + 2NaOH  Mg(OH)2↓ + 2NaCl

3. Chlorides

The metal chloride can be formed by heating the metal in a stream of chlorine gas.
 

Mg + Cl2 MgCl2

4. Carbonates

When calcium carbonate (limestone) is in contact with rain water over a period of time, there is a reaction that produces calcium hydrogen carbonate. This is the compound responsible for temporary hard water.

CaCO3 + H2O + CO2 Ca(HCO3)2
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