Question

$50ml$ of $0.1MHCl$ is mixed with $49.9ml$ of $0.1MNaOH$. The $pH$ of the resulting solution is:

• A. $4$
• B. $1$
• C. $7$
• D. $3$

Answer 1

The correct option is D $3$

$50$ $mL$ $HCl$ $0.1$ $M\Rightarrow 5$ $m$ $mol$ of $\left[H^{+}\right]$

$49.9$ $mL$ of $0.1$ $M$ $NaOH\Rightarrow 4.9$ $m$ $mol$ of $\left[O{H}^{-}\right]$

$0.1$ $m$ $mol$ of $\left[H^{+}\right]$ is left in $100$ $mL$ of water.

Concentration $=\frac{0.1\times {10}^{-3}}{100\times {10}^{-3}}={10}^{-3}$

$\therefore \left[H^{+}\right]={10}^{-3}$

$pH=-lo{g}_{10}\left[H^{+}\right]$

$pH=3$