Equilibrium · pH of weak acid and buffer

At 25$^\circ$C, 20.0 mL of 0.2 M weak monoprotic acid HX is titrated against 0.2 M NaOH. The pH of the solution (a) at the start of the titration (when NaOH has not been added) and (b) when 10 mL of NaOH is added respectively, are :

Given : $K_\mathrm{a} = 5\times10^{-4}$, p$K_\mathrm{a} = 3.3$, $\alpha \ll 1$