Reactions of Group 2 Compounds

This lesson covers: 

  1. Role of group 2 oxides as bases
  2. Applications of group 2 elements and compounds

Group 2 oxides are bases

The oxides of group 2 elements (MO) are basic and alkaline:

They readily react with water to form metal hydroxides that dissolve in water:

  • MO(s) + H2O(l) ➔ M(OH)2(aq)

This releases hydroxide ions (OH-) making the solutions strongly alkaline. For example:

BaO(s) + H2O(l) ➔ Ba2+(aq) + 2OH-(aq)

The pH of the resulting solutions increases down the group as the solublity of the hydroxides increases.

An exception is MgO which reacts slowly and has low solubility.

Applications of group 2 elements and compounds

Group 2 elements and compounds have important practical uses including:


Calcium hydroxide for neutralising soil acidity

Calcium hydroxide (Ca(OH)2), also called slaked lime, counters high acidity in soils by neutralising hydrogen ions. It is spread over agricultural fields to raise pH levels optimal for healthy crop growth. The ionic equation for the neutralisation is:

H+(aq) + OH−(aq) ➔ H2O(l)


Magnesium hydroxide as an antacid

Magnesium hydroxide (Mg(OH)2) is an effective antacid, which is a base substance that neutralises stomach acid. It works by reacting with the hydrochloric acid in the stomach, neutralising the excess acid that causes the symptoms of indigestion. The ionic equation for the neutralisation is:

H+(aq) + OH−(aq) ➔ H2O(l)