question_answer 126)

  Ionisation constant of a weak base MOH, is given by the expression \[{{K}_{b}}=\frac{[{{M}^{+}}][O{{H}^{-}}]}{[MOH]}\] Values of ionisation constant of some weak bases at a particular temperature are given below:  

Base	Dimethylamine	Urea	Pyridine	Ammonia
\[{{K}_{b}}\]	\[5.4\times {{10}^{-4}}\]	\[1.3\times {{10}^{-14}}\]	\[1.77\times {{10}^{-9}}\]	\[1.77\times {{10}^{-5}}\]

  Arrange the bases in decreasing order of the extent of their ionisation at equilibrium. Which of the above base is the strongest?

Answer:

    \[\frac{\text{Dimethyl amine  Ammonia  Pyridine  Urea}}{\text{Decreasing extent of ionization}}\] Dimethyl amine is the strongest base.