HARDNESS OF WATER
INTRODUCTION.
Water is very essential substance for all living things. Over 70% of the earth is water and there are different sources of water for daily use. These sources include rivers, lakes, wells, ponds, springs, and streams.
Water can also be obtained from taps that are supplied with treated from the local or nearest water works.
In some places, water lathers easily with soap, this water is said to be soft. In other places, the same amount of soap would give scum and very little lather. This water is said to be hard. Scum is an insoluble layer of impurities that accumulates at the surface of a liquid, especially water.
Hardness of water is caused by dissolved calcium and magnesium compounds. They include calcium, calcium hydrogen carbonate, magnesium sulphate and magnesium hydrogen carbonate. For example
Calcium sulphate + sodium stearate → calcium stearate + sodium sulphate
(Hardness) (Soap) (Scum)
The soap and the hardness join to form scum. The other compound sodium sulphate which is formed dissolves in water.
Calcium hydrogen carbonate is the most common cause of hardness of water. It forms when rain falls on the rocks of limestone and chalk, which are mainly composed of the insoluble calcium carbonate. As the rain falls through the air, it dissolves carbon dioxide to form weak acidic solution. This solution is able to attack the calcium carbonate to form the soluble calcium hydrogen carbonate.
Water + carbon dioxide + calcium carbonate → calcium hydrogen carbonate
H2O(l) + CO2(g) +CaCO3(s) → Ca (HCO3)2(aq)
Dolomite and gypsum are other rocks that are sources of hard water.
TYPES OF HARDNESS OF WATER.
There are two types of hardness of water, namely Temporary and Permanent hardness of water.