Class 11 NEET Chemistry Equilibrium Questions Part 1

Let us consider the formation of a salt of a weak acid and a strong base.
In−+H2O⇌HIn+OH−
Kh=‌

[HIn][OH−]

[In−]

....(1)
Other equations present in the solution are
HIn⇌H++In−
H2O⇌H++OH−
KIn=‌

[H+][In−]

[HIn]

....(ii)
Kw=[H+][OH−]......(iii)
From (ii) and (iii),
‌

Kw

KIn

=‌

[HIn][OH−]

[In−]

=Kh.....(iv)
[OH−]=‌

Kw

KIn

‌

[In−]

[HIn]

pKw−pOH=pKIn+log‌

[In−]

[HIn]

or, ‌‌pH=pKIn+log‌

[In−]

[HIn]

i.e. log‌

[In−]

[HIn]

=pH−pKIn