The Bronsted-Lowry theory states that an acid is a substance which donates protons, and a base is a substance that accepts protons. The equilibrium law can be applied to aqueous solutions of acids. For example, the following equilibrium is established in an aqueous. solution of ethanoic acid: CH3COOH(aq) + H20(l) CH3COO-(aq) + H30+(aq) The equilibrium constant is given by: Or Ka is the Acid dissociation constant which is a measure of the strength of an acid. pKa = lgKa - for most acids this gives the range of values between 0-14. Strong acids have low pKa values. Kw is the ionic product of water, it is based on the equilibrium that occurs due to waters ability to self-ionise. Kw = [H+][OH-] At 25°C it has a value of 1.0 x 10-14 pKw = 14. To calculate pH: pH = -lg [H+] A buffer is a solution in which the pH of which does not change significantly when small amounts of acid or base is added to it. Solubility product is a measure of a compounds solubility: Ksp.