Specific Ion Exchanger Reactions:

Suppose a solution holding Na⁺ ions is passed by hydrogen resin.  From the associative affinities provided previously here Na⁺ ions are attracted to the resin more strongly than H⁺ ions.  Therefore, Na⁺ ions will displace H⁺ ions from the resin or, alternatively, Na⁺ ions and H⁺ ions exchange place among resin and solution.  The procedure could be described through the following equilibrium reaction.

H - R+ Na⁺    ↔ Na - R+ H⁺

In most practical conditions, a solution holding impurities at low concentrations is passed by a huge amount of resin.  Through LeChatelier's Principle, the equilibrium of Reaction (4-1) is forced far to the right. Equilibrium is displaced so far in which, for practical reasons, all Na⁺ ions are erased from solution and exchange through H⁺ ions.  Conclusion, the solution will be acidic since of the excess of H⁺ ions.

If a solution containing Cl^- ions is passed by hydroxyl resin, Cl^- ions will be removed according to the subsequent reaction.

R - OH + Cl^-  ↔ R - Cl + OH^-

Once more, for a dilute solution and a huge amount of resin, a removal of Cl^- ions is fundamentally 100 % complete.  By this case, the last solution will be basic since of the excess of OH^- ions.

Let consider a situation in that the entering impurities are calcium sulfate (CaSO₄) and sodium chloride (NaCl), or the ion exchanger is a combination of both hydrogen and hydroxyl resins (mixed-bed).

H-R + R- OH + Ca⁺⁺ + SO₄⁼ → Ca - R +   R - SO₄ + H⁺  + OH^-

H-R + R- OH + Na⁺  + Cl^- → Na - R +      R - Cl + H⁺     + OH^-