question_answer 1)

A 0.02 M solution of pyridinium hydrochloride has pH = 3.44. Calculate the ionisation constant of pyridine.

Answer:

Pyridinium hydrochloride is the salt of weak base and strong acid, its pH can be calculated using following relation: \[pH=\frac{1}{2}[p{{K}_{w}}-p{{K}_{b}}-logC]\] \[3.44=\frac{1}{2}[14-p{{K}_{b}}-log0.02]\] \[3.44\times 2=14-p{{K}_{b}}-[-1.6989]\] \[p{{K}_{b}}=14+1.6989-2\times 3.44=8.8189\] \[{{K}_{b}}=\text{Anitlog}[-p{{K}_{b}}]\] \[=\text{Anitlog}[-8.8189]\] \[=1.517\times {{10}^{-9}}\]