Question

What causes the temporary and permanent hardness of water ?

Answer 1

Hint: Temporary and permanent hardness of water is due to the compounds present in the respective types of water. Determine the salts that can be separated from water by simple boiling or heating and the ones that do not separate. On this basis you can explain temporary and permanent hardness of water.

Complete step by step answer:
Hard water is the water having high mineral content in contrast to soft water. Hard water is formed when water percolates through deposits of ores like limestone, chalk or gypsum which contain the ions of calcium and magnesium.
Hardness of water can be of two types namely, Temporary and permanent hardness.
Temporary hardness is a type of water hardness caused by the presence of dissolved salts of bicarbonate minerals like calcium bicarbonate and magnesium bicarbonate. Temporary hardness can be removed by simple heating of the solution or through the process of lime softening.
Permanent hardness contains mainly salts like calcium sulphate and magnesium sulphate. These salts cannot be removed by simple boiling. This is because these salts do not precipitate when the solution is heated.

Additional Information:
Calgon is a chemical compound with the composition sodium hexametaphosphate used for treating hard water.
The chemical reaction taking place is given below:
${{[N{{a}_{4}}{{P}_{6}}{{O}_{18}}]}^{2-}}\text{ + }C{{a}^{2+}}\text{ }\to \text{ }\!\![\!\!\text{ }N{{a}_{2}}Ca{{P}_{6}}{{O}_{18}}{{]}^{2-}}$

Similar to the way Calgon reacts with calcium ions in hard water, it reacts with magnesium ions and forms a complex removing the hardness of water. The reaction is given below:
${{[N{{a}_{4}}{{P}_{6}}{{O}_{18}}]}^{2-}}\text{ + M}{{\text{g}}^{2+}}\text{ }\to \text{ }\!\![\!\!\text{ }N{{a}_{2}}Mg{{P}_{6}}{{O}_{18}}{{]}^{2-}}$

Note: Hard water is considered not fit for domestic use for various reasons. One such reason is its interference in the micelle formation of soap particles. Due to high mineral content, the oil particles form a complex which sticks to the human skin instead of being washed away. This is called scum and is an undesired result of hard water.