For sodium acetate solution in water, the given equilibrium reaction occur: CH3COO−(aq)+H2O(l)hydrolysis⇌CH3COOH(aq)+OH−(aq)
Which of the following describes the correct relation ?
(where h is the degree of hydrolysis of salt)
A
h=√Kw⋅CKa
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B
h=√KwKa⋅C
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C
h=√Ka⋅CKw
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D
h=√KaKw⋅C
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Solution
The correct option is Bh=√KwKa⋅C Salt of weak acid and strong base. If C is the concentration and h is the degree of hydrolysis, then hydrolysis of anion takes place as following : CH3COO−C(1−h)(aq)+H2O(l)hydrolysis⇌CH3COOHCh(aq)+OH−Ch(aq)
Kh=[CH3COOH][OH−][CH3COO−]=Ch×ChC(1−h)=Ch21−h
and, CH3COOH⇌CH3COO−+H+Ka=[CH3COO−][H+][CH3COOH]H2O⇌H++OH−Kw=[H+][OH−]
We see that Kh=KwKa=Ch21−hForh<0.1Then,1−h≈1KwKa=Ch2h=√KwKa⋅C