What is the autoionization constant of water (Kw) at 25°C?

The autoionization constant of water, also known as the ion product of water, is a critical value in chemistry, particularly in acid-base chemistry. At 25°C, the value of Kw is 10⁻¹⁴. This constant represents the equilibrium constant for the self-ionization reaction of water, which can be expressed as:

[ 2 H_2O (l) \rightleftharpoons H_3O^+ (aq) + OH^- (aq) ]

In this reaction, two water molecules donate a proton (H⁺) and create hydronium (H₃O⁺) and hydroxide (OH⁻) ions. The ion product of water is a reflection of the concentrations of these ions in pure water, where at 25°C, each of them has a concentration of approximately 10⁻⁷ M, leading to the product:

[ [H_3O^+][OH^-] = (10^{-7})(10^{-7}) = 10^{-14} ]

The significance of Kw is that it dictates the relationship between the concentrations of hydronium and hydroxide ions in any aqueous solution. It remains constant at a given temperature, thus