Neutral, Acidic and Basic Solutions

In pure water H+ (aq) and OH (aq) ions are produced in equal numbers as a result of dissociation of water and therefore, their concentrations are also equal.

1. Neutral Solutions

In all neutral aqueous solutions, the concentrations of H+ (aq) and OH (aq) ions remains equal.

[H+] = [OH]

The neutral solution is the one in which the concentrations of H+ and OH ions are equal.

2. Acidic Solutions

Acids furnish H+ (aq) ions in their solutions resulting in increase in their concentration. Thus, in acidic solutions

[H+] > [OH]

[H+] > 1.0 × 10–7 mol L–1

The acidic solution is the one in which the concentration of H+ (aq) is greater than that of OH (aq) ions.

The ionic product of water Kw is constant at a given temperature. It can remain so only if the concentration of OH (aq) ions decreases.

[OH] < 10–7 mol L–1

3. Basic Solutions

Bases furnish OH (aq) ions in their solutions. This results in an increase in their concentration. Therefore, in basic solution

[OH] > [H+]

[OH] > 1.0 × 10–7 mol L–1

The basic solution is the one in which the concentration of H+ (aq) ions is smaller than that of OH–1 (aq) ions. Here also, because of constancy of ionic product of water Kw, the concentration of H+ (aq) decreases.

[H+] < 1.0 × 10–7 mol L–1