Ionic Strength: Overview

When a salt dissolves in water, the cation and anion dissociate. Each ion attracts ions of the opposite charge due to electrostatic attraction.

This ionic atmosphere around the ions weakly shields the charge of the central ion.

The effectiveness of the ionic atmosphere shielding is related to the ionic strength, which is determined by the concentration and the charge of the ions.

Formally symbolized as I, the ionic strength of a solution incorporates the total concentration of all the ions in the solution and is proportional to the molar concentration of the salt.

As the charge of the ion is squared in the calculation, the greater the charge on an ion, the more significant its contribution to the ionic strength value.

For example, the ionic strength of a potassium nitrate solution is the same as its concentration.

However, the ionic strengths of solutions of potassium sulfate, a 2:1 electrolyte, and calcium sulfate, a 2:2 electrolyte, are three and four times their concentrations, respectively.