Soft water - water softening methods

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Soft water:

The water which does not contain HCO₃^-, Cl^-, SO₄^2- salt of Ca²⁺, Mg²⁺, Fe²⁺, Al³⁺ & form foam easily by reacting with soap is called soft water e.g. Rain water.

Water softening methods:

Water softening process is done in order to remove Ca²⁺ and Mg²⁺ ions from water. Since, Na and Mg are nonvolatile salt, it is needed to separate them from water by precipitation or any other way.

There is a simple process of softening temporary hardness of water and it is boiling. When water is boiled the dissolved Calcium & Magnesium salt converted to Calcium Carbonate and Magnesium Carbonate & precipitated. That way they can be separated from water. The reaction is here:

Ca(HCO₃) --> CaCO₃ + CO₂ + H₂O

                            ppt.

Mg(HCO₃) --> MgCO₃ + CO₂ + H₂O

                            ppt.

For both temporary and permanent hard water there are three industrial softening methods. These are:

1. Soda lime mthod
2. Base exchange method (permutit)
3. Demineralisation method.