Question

A solution of $0.1 \,M$ weak base $(B)$ is titrated with $0.1\, M$ of a strong acid $(HA)$. The variation of $pH$ of the solution with the volume of $HA$ added is shown in the figure below. What is the $p K_{ b }$ of the base? The neutralization reaction is given by $B + HA \rightarrow BH ^{+}+ A ^{-}$

Answer 1

• From the graph, it is clear, that the equivalence point is reached at a titre value of 6 mL i.e. when 6 mL of HA are added base (B) is completely neutralized.
  • So it will be half neutralized at titre value of 3 mL; when 3 mL of HA is added, ‘B’ is half – neutralized.
  • So at this stage it will form a best buffer.
  • So, pKb of weak base = 3