Question

The pH of $10^{-8}MHCl$ solution is

• A. 8
• B. 6.9586
• C. More than 8
• D. Slightly more than 7

Answer 1

Answer: (B)

As $HCl$ solution is acidic in nature and the $pH$ of an acidic solution cannot exceed more than $7$ Thus, the answer must be $6.9586$

We can also find this answer through calculations From acid, $\left[H^{+}\right]=10^{-8}M$

But the $\left[H^{+}\right]$ ions from water, i.e., $\left[H^{+}\right]=10^{-7}M$

cannot be neglected in comparison to $10^{-8}M$ The $pH$ can be calculated as follows

From acid, $\left[H^{+}\right]=10^{-8}M$

From water, $\left[H^{+}\right]=10^{-7}M$

$\therefore$ Total $\left[H^{+}\right]=10^{-8}+10^{-7}=10^{-8}(1+10)$

$=11\times 10^{-8}M$

$\therefore pH=-\log \left[H^{+}\right]$

$=-\log \left(11\times 10^{-8}\right)$

$=-\left[\log 11+\log 10^{-8}\right]$

$=-[1.0414-8]=6.9586$