• The characteristics of the pH curves produced by the different combinations of strong and weak acids and bases.

• An acid–base indicator is a weak acid or a weak base where the components of the conjugate acid–base pair have different colours.

• The relationship between the pH range of an acid–base indicator, which is a weak acid, and its pKa value.

• The buffer region on the pH curve represents the region where small additions of acid or base result in little or no change in pH.

• The composition and action of a buffer solution.

• The general shapes of graphs of pH against volume for titrations involving strong and weak acids and bases with an explanation of their important features.

• Selection of an appropriate indicator for a titration, given the equivalence point of the titration and the end point of the indicator.

• While the nature of the acid–base buffer always remains the same, buffer solutions can be prepared by either mixing a weak acid/base with a solution of a salt containing its conjugate, or by partial neutralization of a weak acid/base with a strong acid/base.

• Prediction of the relative pH of aqueous salt solutions formed by the different combinations of strong and weak acid and base.

• Only examples involving the transfer of one proton will be assessed. Important features are:

– intercept with pH axis

– equivalence point

– buffer region

– points where pKa = pH or pKb = pOH.

• For an indicator which is a weak acid:

– HIn(aq) <------> H+(aq) + In-(aq)

Colour A Colour B

– The colour change can be considered to take place over a range of pKa ± 1.

• For an indicator which is a weak base:

– BOH(aq) B+(aq) + OH-(aq) Colour A Colour B

• Examples of indicators are listed in the data booklet in section 22.

• Salts formed from the four possible combinations of strong and weak acids and bases should be considered. Calculations are not required.