Question

Arrange the following in increasing order of their $p{K}_a$ values.
(x) $C{H}_{3}S{O}_{3}H$
(y) $C{H}_{3}COOH$
(z) $C{H}_{3}OH$

• A. y < x < z
• B. x < y < z
• C. y < z < x
• D. x < z < y

Answer 1

The correct option is B x < y < z

$\text{Acidic strength}\propto \text{stability of conjugate base}$
Higher the acidic strength, lower the $p{K}_a$
$\text{Stability of conjugate base}\propto \text{Stability of resonance hybrid}\propto \text{Number of equivalent resonating structure}$
So stability order is x > y > z
Acidic strength order is x > y > z and hence $p{K}_a$ is z > y > x.