Question

When $1ml$ of $0.1$ $NHCl$ is added to $1$ litre of a solution of $pH$ value $4$, the $pH$ will be near:

• A. $5$
• B. $4.477$
• C. $3$
• D. $3.7$

Answer 1

The correct option is D $3.7$

$pH=-log[H{]}^{+}=4$.

Hence, $[H{]}^{+}={10}^{-4}$.

When two solutions are mixed, the expression for the hydrogen ion concentration of the resulting solution is,

$[H{]}^{+}=\frac{N_1{V}_1+N_2{V}_2}{V_1+V_2}$.

Substitute values in the above expression.

$[H{]}^{+}=\frac{0.1\times 0.001+{10}^{-4}\times 1}{0.001+1}$

$[H{]}^{+}=2\times {10}^{-4}M$

$pH=-log[H{]}^{+}=-log(2\times {10}^{-4})=3.7$.