Question

The pH of a solution made by mixing 50 mL of 0.2 M $HCl$ and 75 mL of 0.1 M $NaOH$ is :

• A. $3$
• B. $13$
• C. $5$
• D. $1.7$

Answer 1

The correct option is D $1.7$

We know, $pH=-log\left[H^{+}\right]$

Here, remaining concentration of hydrogen ion is calculated below :

$HCl+NaOH\to NaCl+H_{2}O$

$50\times 0.2$ $75\times 0.1$

$7.5$ mL of $NaOH$ reacts with $7.5$ mL of $HCl$ leaving behind $2.5$ mL of $HCl$.

$\left[H^{+}\right]=\frac{2.5}{125}=2\times {10}^{-2}$

Therefore, $pH=-log\left[H^{+}\right]=2-log2=1.7$

Hence, the correct option is D.