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

$\text{K}_\text{b}=\frac{[\text{M}^+][\text{OH}^-]}{[\text{MOH}]}$

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

Base
Dimethylamine
Urea
Pyridine
Ammonia
Kb
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

Greater is the ionization constant (Kb) of a base, greater is the ionization of the base. Order of extent of ionization at equilibrium is dimethylamine > ammonia > pyridine > urea. Dimethylamine is the strongest base due to maximum value of Kb.

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