Question

$5$ ml of $0.4NNaOH$ is mixed with $20$ ml of $0.1N$ $HCl$. The pH of the resulting solution will be:

• A. $6$
• B. $7$
• C. $8$
• D. $5$

Answer 1

Answer: (B)

$7$

$5$ ml of $0.4NNaOH$ is mixed with $20$ ml of $0.1NHCl$. The pH of the resulting solution will be $7$.

Number of milligram equivalents of $NaOH$ $=5\times 0.4=2$.

Number of milligram equivalents of $HCl$ $=20\times 0.1=2$.

Thus, $NaOH$ will be completely neutralised with $HCl$ to form salt $NaCl$. $NaCl$ is a salt of strong base with strong acid.
Such salts do not undergo hydrolysis and give neutral aqueous solutions.

Hence, option $B$ is correct.