Question

What is meant by the temporary and permanent hardness of water and how is it caused?

Answer 1

Hardness of water

• Water that does not give lather with the soap is called hard water.
• The hardness of water is due to the presence of soluble bicarbonates, chlorides, and sulfates of calcium and magnesium.

Temporary hardness of water

• Hard water contains soluble salts of magnesium and calcium in the form of hydrogen carbonates ( ${\mathrm{MgHCO}}_3$ and ${\mathrm{CaHCO}}_3$) is called temporary hardness of the water.
• Magnesium bicarbonate ${\mathrm{MgHCO}}_3$and calcium bicarbonate ${\mathrm{CaHCO}}_3$are responsible for causing the temporary hardness of the water.
• Temporary hardness can be removed by boiling it, as the magnesium carbonates get converted to magnesium hydroxide, which is insoluble in water and so can be easily filtered out.

Permanent hardness of water

• Hard water contains soluble salts of calcium and magnesium that are present in the form of sulfides, nitrates, or chlorides are called permanent hardness of the water.
• The permanent hardness of water is caused by the presence of soluble chlorides and sulpates of magnesium and calcium i.e ${\mathrm{CaCl}}_{2,}{\mathrm{CaSO}}_4$and ${\mathrm{MgCl}}_2,{\mathrm{MgSO}}_4$
• The permanent hard water can be converted into soft water by treating it with washing soda and some other methods.