Question

Ionisation constant of a weak base MOH, is given by the expression

`K_b = ([M^+][OH^-])/([MOH])`

Values of ionisation constant of some weak bases at a particular temperature are given below:

Base	Dimethylamine	Urea	Pyridine	Ammonia
\[\ce{K_b}\]	5.4 × 10–4	1.3 × 10–14	1.77 × 10–9	1.77 × 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 1

Higher the value of \[\ce{K_b}\] stronger will be the base. 

K_b- 5.4 × 10^–4 > 1.77 × 10^–5 > 1.77 × 10^–9 > 1.3 × 10^–14

Decreasing order of basic strength. 

Dimethylamine > Ammonia > Pyridine > Urea

Hence among the given bases, the strongest base is Dimethylamine.