Explain the Dissociation of bases in water.

The ionization constant or dissociation of a base BOH in water may be represented as:
BOH (aq) <---------> B+ (aq) + OH (aq)
Therefore the ionization constant of the base, Kb,
Therefore, Kb = [B+] [OH] / [BOH]
(Concentration of water remains constant)
If c is the number of moles of the base in one litre of the solution and α is the degree of ionization, then the concentrations of each species at equilibrium are:
[B+] = cα
[OH] = cα
[BOH] = c (1 – α)
Therefore, Kb = (cα) X (cα) / c (1 – α)
But for weak bases, α is very small so that 1 – α ≈ 1
Therefore,
Kb = (cα) 2
α= (Kb / c) 1/2
And
[OH] = c x (Kb / c) 1/2
[OH] = (Kb. c) 1/2

Category: Ionic Equilibria

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