Question

Equal volumes of two $HCl$ solutions of $pH=3$ and $pH=5$ were mixed. What is the $pH$ of the resulting solution?
(Given: $\log \left(0.505\right)=-0.3$)

• A. $2.7$
• B. $4.3$
• C. $3.7$
• D. $3.3$

Answer 1

The correct option is D $3.3$

When equal volumes are taken, the concentration becomes half.
$\therefore \left[H^{+}\right]=\frac{1}{2}({10}^{-3}+{10}^{-5})$
$=0.505\times {10}^{-3}$
$\therefore pH=-\log \left[H^{+}\right]=-\log (0.505\times {10}^{-3})=3.3$