Question

The $pH$ of $0.1M$ solution of aniline is $8.8$. Its $p{K}_b$ value will be:

• A. $7.82$
• B. $6.18$
• C. $9.40$
• D. $8.40$

Answer 1

The correct option is C $9.40$

Aniline $C_6{H}_{5}N{H}_2$ is a weak base.
Given, $pH=8.8,c=0.1M$
we know $pH+pOH=14$
$8.8+pOH=14$
$pOH=14-8.8=5.2$

Also, $pOH=\frac{p{K}_b-logc}{2}$
putting the $c$ and $pOH$ values, we get
$5.2=\frac{p{K}_b-log0.1}{2}$
$10.4=p{K}_b-log0.1$
$10.4=p{K}_b+1$
$p{K}_b=10.4-1$
$p{K}_b=9.4$