## pH for strong acid and strong base titrations

If there is a perfect neutralisation reaction of a strong acid by a strong base, the resulting solution will have a pH that may be assumed to be almost identical to the pH for water at that temperature. So, the pH at the equivalence point for a strong acid and strong base titration is approximately equal to 7.0 at 298K.

## Buffer action

Definition A buffer solution maintains an approximately constant pH, despite dilution or addition of small amounts of acid or base. Acidic buffer solutions contain a mixture of a weak acid (e.g. CH3COOH) and the salt of that weak acid (e.g. CH3COONa). Basic buffer solutions contain a mixture of a weak base (e.g. NH3(aq)) and the salt of that weak base (e.g. NH4Cl). Calculating the pH of a

## pH curves titrations and indicators

pH curves Understand typical pH curves for acid–base titrations in all combinations of weak and strong monoprotic acids and bases. Students should be able to: • sketch and explain the shapes of typical pH curves • use pH curves to select an appropriate indicator. A titration curve shows a graphical representation of the neutralisation reaction occurring between an acid and a base.

## Weak acids and bases Ka for weak acids

Weak acids and weak bases dissociate only slightly in aqueous solution. Ka is the dissociation constant for a weak acid. pKa = –log10 Ka Examples of calculating pH in weak acids IMPORTANTLY, there is no requirement to repeatedly state the proof for the derivation of the pH in a weak acid calculation. Full credit will be awarded to candidates if you simply

## The ionic product of water Kw

Water is slightly dissociated. Kw is derived from the equilibrium constant for this dissociation. Kw = [H+][OH–] The value of Kw varies with temperature. The ionic product, Kw = [H+][OH–] may be used to determine the pH of strong bases (click here)   Examples of calculations using Kw