In pure water, one H2O molecule donates proton and acts as an acid and another H2O molecule accepts a proton and acts as a base at the same time. So, the following equilibrium exists –
Dissociation constant K = \(\frac{[H_3O^+][OH^-]}{[H_2O]}\)
The concentration of water is omitted from the denominator as water is a pure liquid and its concentration remains constant. [H2O] is incorporated with in the equilibrium constant to give a new constant, Kw, which is called the ionic product of water.
Kw = [H+][OH-]
The value of ionic product (Kw) increases with increase in temperature.
