Ionic Equilibrium Past Papers Collection MCQ and Structured Question 1983 - 2014 Download Ionic Equilibrium H 2 O is the medium of biological systems one must consider the role of this molecule in the dissociation of ions from biological molecules. Water is essentially a neutral molecule but will ionize to a small degree. This can be described by a simple equilibrium equation: H 2 O ↔ H + + OH – This equilibrium can be calculated as for any reaction: Since the concentration of H 2 O is very high (55.5M) relative to that of the [H + ] and [OH – ], consideration of it is generally removed from the equation by multiplying both sides by 55.5 yielding a new term, K w : K w = [H + ][OH – ] This term is referred to as the ion product. In pure water, to which no acids or bases have been added: K w = 1 x 10 –14 M 2 As K w is constant, if one considers the case of pure water to which no acids or bases have been added: [H + ] = [OH - ] = 1 x...