Question

What is meant by ‘demineralised’ water and how can it be obtained?

Answer 1

Demineralised water is free from all soluble mineral salts. It does not contain any anions or cations.

Demineralised water is obtained by passing water successively through a cation exchange (in the H⁺ form) and an anion exchange (in the OH^– form) resin.

During the cation exchange process, H⁺ exchanges for Na⁺, Mg²⁺, Ca²⁺, and other cations present in water.

……. (1)

In the anion exchange process, OH^– exchanges for anions such as etc. present in water.

OH^– ions liberated in reaction (2) neutralize H⁺ ions liberated in reaction (1), thereby forming water.