Q. Which one of the following statement is not true?
A) The conjugate base of $H_{2}PO_{4}^{-}\ is\ HPO_{4}^{2 -}$
B) $pH + pOH = 14$ for all aqueous solutions
C) $The\ pH\ of\ 1 \times 10^{- 8}\ M\ HCl\ is\ 8$
D) 96500 C of electricity when passed through a $CuSO_{4}$ solution deposit 1 g equivalent of copper at the cathode
Explanation
(c)
$1 \times 10^{- 8}\ M\ HCl$ solution $H_{2}O$ is also present there which also undergoes self ionisation.
$H_{2}O \rightleftharpoons H^{+} + OH^{-}$
$10^{- 7}\ M\ at\ 25℃$
If it is taken simply even without common ion effect, higher concentration must be considered which is $10^{- 7}M\ but\ H^{+}\$from HCl decreases self ionisation which further decreases self ionisation, hence $\left\lbrack H^{+} \right\rbrack$from$\ H_{2}O$.
Hence, net concentration must be smaller than $10^{- 7}$ M.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.