Question

Which one of the following statements is not true?
Given: log 11=1.0414

• A. $pH+pOH=14$ for all aqueous solutions
• B. The pH of $1\times {10}^{-8}MHCl$ is 8
• C. The conjugate base of $H_{2}P{O}_4^{-}$ is $HP{O}_4^{2-}$
• D. All of the above.

Answer 1

The correct option is B The pH of $1\times {10}^{-8}MHCl$ is 8

a) $pH+pOH=14$ for all aqueous solutions at ${25}^{o}C$
b) pH of an acidic solution should be less than 7. The reason is that from $H_{2}O$, $\left[H^{+}\right]={10}^{-7}M$ cannot be neglected in comparison to ${10}^{-8}M.$
The pH can be calculated as:
from acid, $\left[H^{+}\right]={10}^{-8}M.$
from $H_{2}O,\left[H^{+}\right]={10}^{-7}M$
$\therefore$ $\text{Total}\left[H^{+}\right]={10}^{-8}+{10}^{-7}$
$\text{Total}\left[H^{+}\right]={10}^{-8}(1+10)$
$\text{Total}\left[H^{+}\right]=11\times {10}^{-8}$
$\therefore pH=-log\left[H^{+}\right]=-log(11\times {10}^{-8})$
$pH=-[log11+8log10]$
$pH=-[1.0414-8]$
$pH=6.9586$
c) The conjugate base of $H_{2}P{O}_4^{-}$ is $HP{O}_4^{2-}.$