Question

The pH of the solution obtained by mixing equal volumes of $HCl$ solution $(pH=4)$ and 0.0019 M $HCl$ solution would be:

• A. $3$
• B. $5$
• C. $9$
• D. $11$

Answer 1

The correct option is A $3$

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

For pH $=4$, $\left[H^{+}\right]={10}^{-pH}={10}^{-4}M$

For 0.0019 M HCl, $\left[H^{+}\right]=0.0019M$

If we mix equal volume of both, then conc. of hydrogen ion will become half and resulting conc. of hydrogen ion is

$\left[H^{+}\right]=\frac{{10}^{-4}+0.0019}{2}=0.001M$

So $pH=-log\left[H^{+}\right]=-log{10}^{-3}=3$