question_answer 92)

Ionisation constant of chloroacetic acid is\[1.35\times {{10}^{-3}}\].What will be the pH of 0.1 M acid and 0.1 M salt solution?

Answer:

pH of acid = \[-\log \sqrt{C{{K}_{a}}}\] \[=-\log \sqrt{0.1\times 1.35\times {{10}^{-3}}}\] \[=1.934\] pH of salt = \[\frac{1}{2}[p{{K}_{w}}+p{{K}_{a}}+logC]\] \[=\frac{1}{2}[14+(-log1.35\times {{10}^{-3}})+log0.1]\] \[=\frac{1}{2}[14+2.869-1]\] \[=7.93\] When the salt and acid are present together, it will be a buffer solution. \[\therefore \] \[pH=p{{K}_{a}}+\log \frac{[Salt]}{[Acid]}\] \[=2.869+\log \frac{0.1}{0.1}=2.869\]