Question

Equal volumes of two $HCl$ solutions of $pH=3$ and $pH=5$ were mixed. What is the $pH$ of the resulting solutions?

• A. 4.3
• B. 4
• C. 4.5
• D. 3.3

Answer 1

The correct option is D 3.3

Since equal volumes of two $HCl$ solutions of $pH=3$ and $pH=5$ were mixed, the concentration of $H^{+}$ ion in the new solution will be

$\left[H^{+}\right]=\frac{{10}^{-3}\times 1+{10}^{-5}\times 1}{2}$ $\Rightarrow \left[H^{+}\right]=5.05\times {10}^{-4}Again,pH=-log\left[H^{+}\right]=-log[5.05\times {10}^{-4}]$
$\Rightarrow pH=3.3$