Ncert Exercises & Solutions

Discuss briefly de-mineralisation of water by ion exchange resin.

Water which is free from all soluble minerals salts is called demineralised water. Demineralised water is obtained by passing water successively through a cation exchange and an anion exchange resins.

In cation exchanger, Ca²⁺, Mg²⁺, Na⁺ and other cations present in water are removed by exchanging them with H⁺ ions while in anion exchanger,

{Cl}^{-}, {HCO}_{3}^{-}, {SO}_{4}^{2 -},

etc., present in water are removed by exchanging them with OH^- ions.

\underset{(Released in cation exchanger)}{H^{+}} + \underset{(Released in anion exchanger)}{{OH}^{-}} \to H_{2} O

Synthetic ion exchange resis are of two types.

Cation exhcange resins contain large organic molecule with SO₃H group are water soluble. It is changed to RNa by treating it with NaCl. The resin RNa exchanges Mg²⁺ and Ca²⁺ ions present in hard water to make the water soft.

2 RNa (s) + M^{2 +} (aq) \to R_{2} M (s) + 2 {Na}^{+} (aq) (M = {Ca}^{2 +} or {Mg}^{2 +})

The resin can be regenerated by passing NaCl (aqueous solution) in it.

Pure demineralised (deionised) water is obtained by passing water successively through a cation exchange and anion exchange resins. In the cation exchange process.

2 RH (s) + M^{2 +} (aq) ⇌ \underset{(Cation exchange}{{MR}_{2} (s) + 2 H^{+} (aq)}

resin in the H^{+} form)

H⁺ exchanges for Ca²⁺, Mg²⁺ and other cations present in water.

This process results in proton and thus, makes the water acidic. In the anion exchange process

{RNH}_{2} (s) + H_{2} O (l) ⇌ R \overset{+}{N} H_{3} . {OH}^{-} (s)

R \overset{+}{N} H_{3} . {OH}^{-}

is substituted ammonium hydroxide anion exchange resin.

R \overset{+}{N} H_{3} . {OH}^{-} (s) + X^{-} (aq) ⇌ R \overset{+}{N} H_{3} . X^{-} (s) + {OH}^{-} (aq)

NEET Information

courses

Company

Botany Questions

Chemistry Questions

Physics Questions

Zoology Questions