Ionization constant of a weak base


Ionization constant of a weak base MOH is given by the expression

Kb = [M+][OH-]/[MOH-]

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

Base Di-methylamine 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?


The decreasing order of bases based on the ionisation constant at Equilibrium will be;-

Di-methylamine > Ammonia > Pyridine > Urea

The strongest base will be Di-methyl amine as its pKb value is 3.29 and we know that the less the pKb value strong is the base.

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