What factors affect acidity in solution?

Approach this question in a logical manner breaking it down into constituent parts and then explaining these in turn.

1. Give a defination for acidity i.e. pH: pH=-log10[H+] or pKa=-long10Ka

2. The question is concerned with changes in H+ and Ka. Think how the concentration of H+ is affected in solution i.e. bond strength, stability of the conjugate base, solvent properties. If using pKa think about how the equilibrium position is affected by these factors.

3. A more in-depth answer will further explain these factors, in particular further breaking down 'stability of the conjugate base' into inductive and mesomeric conjugation as well as orbital hybridisation. Diagrams (and examples of strong/weak acids) make it easy for the examiner to know that the student understands these concepts.

Note: Solvent effects are not so important at A-level as it is nearly always assumed to be in H2O.