Question

The $pH$ of a buffer solution containing equal molar concentration of a week base and its chloride ($K_b$ for weak base $=2\times {10}^{-5}$) is :

• A. $5$
• B. $9$
• C. $4.7$
• D. $9.3$

Answer 1

The correct option is D $9.3$

For basic buffer
$pOH=p{K}_b+\log \left[\frac{salt}{base}\right]$

Given, $\left[salt\right]=\left[base\right]=1$

$K_b=2\times {10}^{-5}$

$\therefore pOH=p{K}_b=-\log (2\times {10}^{-5})$

$=5-\log 2$

$=5-0.30=4.70$

$pH=14-pOH$

$=14-4.70=9.30$