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 $pK_b$ of the base? The neutralization reaction is given by B + HA $\rightarrow$ BH$^+$ + A$^-$

Answer 1

3

Answer 2

The equivalence point is at 6 mL of HA added. The half-equivalence point is at 3 mL of HA added. At the half-equivalence point, pH = 11, so pOH = 14 - 11 = 3. At the half-equivalence point for a weak base titrated with a strong acid, pOH = $pK_b$. Therefore, $pK_b$ = 3.