Describe the method which is used to provide residual hardness of water lessthan 2ppm. Draw diagram and write equations for the same.

The method used to reduce the residual hardness of water to less than 2ppm is called the Lime-Soda process. This process is typically used in water treatment to soften large amounts of hard water.

Here are the steps involved in the Lime-Soda process:

1. Lime and soda ash are added to the hard water. The lime reacts with the calcium and magnesium ions in the water to form precipitates of calcium carbonate and magnesium hydroxide. The soda ash reacts with the remaining calcium and magnesium ions to form precipitates of calcium carbonate and magnesium carbonate.

2. The precipitates are allowed to settle and are then removed, leaving the water softer.

The chemical reactions involved in this process are as follows:

For lime: Ca(HCO3)2 + Ca(OH)2 → 2CaCO3↓ + 2H2O Mg(HCO3)2 + 2Ca(OH)2 → 2CaCO3↓ + Mg(OH)2↓ + 2H2O

For soda: CaCl2 + Na2CO3 → CaCO3↓ + 2NaCl MgCl2 + Na2CO3 → MgCO3↓ + 2NaCl

Unfortunately, I can't draw diagrams here. But you can easily find diagrams of the Lime-Soda process in water treatment textbooks or online. The diagrams typically show a tank where lime and soda ash are added to the hard water, and another tank where the precipitates are allowed to settle and are then removed.