pH of a buffer solution can be calculated using the following equation:
pKa is given as 5.28
the ratio of A⁻ to HA is given as 1.0 × 10²
putting all the values in the equation;
pH=5.28+log [1.0 × 10²]
pH=7.28
SO, when a buffer solution is made using a weak acid, HA, with a pka of 5.28. if the ratio of A⁻ to HA is 1.0 × 10², the pH of the buffer is 7.28.