Question:
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?
Solution:
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.