Question

The $pH$ of the solution 5 mL of $\frac{M}{5}HCl+10mL$ of $\frac{M}{10}NaOH$ is:

• A. 5
• B. 3
• C. 7
• D. 8

Answer 1

The correct option is C 7

Find milliequivalents of $HCl$ and $NaOH$ and then find which is in excess to know $pH$ of resulting solution.
Given, vol. of $HCl=5$ ml, molarity = M/5
Vol. of $NaOH=10$ mL, molarity = M/10
Milliequivalents of $HCl$ $=5\times \frac{1}{5}=1$
Milliequivalents of $NaOH$ $=10\times \frac{1}{10}=1$
$HCl+NaOH⟶NaCl+H_{2}O$
$\because$ Milliequivalents of $HCl=$ Milliequivalent of $NaOH$
$\therefore$ Solution is neutral and $pH=7$