Question

$20 \,mL$ of $0.1 \,M \,NH _4 OH$ is mixed with $40\, mL$ of $0.05\, M \,HCl$. The $pH$ of the mixture is nearest to:
(Given: $K _{ b }\left( NH _4 OH \right)=1 \times 10^{-5}, \log 2=0.30$, $\log 3=0.48, \log 5=0.69, \log 7=0.84$, $\log 11=1.04$ )

• A. $3.2$
• B. $4.2$
• C. $5.2$
• D. $6.2$

Answer 1

Answer: (C)

$pH =\frac{ pK _{ w }- pK _{ b }-\log C }{2}$
$=\frac{14-5+1.48}{2}=5.24$