Steve Marsden’s

Up to this point our experimental evidence has pointed to pure water being a non-electrolyte. With better instruments it is found that a small number of water molecules actually dissociate:

H2O(ℓ) H+(aq) + OH-(aq)

or using Brønsted conventions:

2 H2O(ℓ) H3O+(aq) + OH-(aq)

This equilibrium lies very far to the left at 25oC. Following the pattern we have used to write Kc expressions for other reactions, the liquid water reactant would be excluded, giving:

Kc = [H+][OH-] = 1.0 x 10-14 = Kw