Question

$K _{ a }$ for butyric acid $\left( C _3 H _7 COOH \right)$ is $2 \times 10^{-5}$. The $pH$ of $0.2 M$ solution of butyric acid is ___$\times 10^{-1}$. (Nearest integer) [Given $\log 2=0.30$ ]

Answer 1

$K _{ a }$ of Butyric acid $\Rightarrow 2 \times 10^{-5} PKa =4.7$
$pH$ of $0.2 M$ solution
$ pH =\frac{1}{2} pK _{ a }-\frac{1}{2} \log C$
$ =\frac{1}{2}(4 \cdot 7) \frac{1}{2} \log (0.2)$
$=2.35+0.35=2.7$
$pH =27 \times 10^{-1}$