Basic Features of Ion Exchange Mechanism:

The term ion exchange generally means exchange of ions of like sign between a solution and a solid highly insoluble within it. The solid called as ion exchanger carries exchangeable cations and anions. While the exchanger is in contact along with an electrolyte, these ions could be exchanged for a stoichiometrically equivalent amount of other ions of similar sign. Carriers of exchangeable cations are called as cation exchangers and carriers of exchangeable anions as anion exchangers. Certain materials are capable of both cation and anion exchange. These are called as amphoteric exchangers.

A classical cation exchange reaction is shown below:

2 NaX + CaCl₂(aq)  ↔ CaX₂  + 2 NaCl_(aq)

Same, typical anion exchange reaction is as follows:

2 XCl + Na₂SO_4(aq)  ↔ X₂SO₄ + 2 NaCl_(aq)

where, X represents a structural unit of the ion exchange.

In the first procedure, a solution containing dissolved CaCl₂, say something such as hard water, is treated along with a solid exchanger, NaX, holding exchangeable Na⁺ ions. An exchanger erases the Ca²⁺ ions from the solution and replaces them along with Na⁺. Thus, a cation exchanger in Na+ form is converted to Ca²⁺ form.

Ion exchange, with extremely few exceptions, is a reversible procedure. In water softening, a cation exchanger has lost its Na⁺ ions and could be reproduced along with a solution of a sodium salt such as NaCl. Ion exchange resembles adsorption in that, in both cases, a dissolved species is taken up through a solid. The features difference among the two is that the ion exchange in contrast to sorption is a stoichiometric process. Each ion removed from the solution is replaced through an equivalent amount of another ionic species of the similar sign. Therefore, in the case of sorption a solute, an electrolyte or non-electrolyte, might be taken up without any species being replaced.