Question

Which of the following statement (s) is (are) correct?

• A. The pH of $1.0 \times 10^{-8} M$ solution of $HCl$ is $8$
• B. The conjugate base of $ H_2PO_4^- $ is $HPO_4^{ 3 - } $
• C. Autoprotolysis constant of water increases with temperature
• D. When a solution of a weak monoprotic acid is titrated against a strong base, at half-neutralisation point $p H = \bigg( \frac{1}{2} \bigg) pK_a$

Answer 1

Answer: (B), (C)

$pH$ of $10^{8} M$ solution will be between $6$ and $7$ but never $8 .$ The conjugate base of an acid is formed by removing a proton $\left(H^{+}\right)$from acid. Therefore, $H P O_{4}^{2-}$ is a conjugate base of $H _{2} PO _{4}^{-}$
$H _{2} O \rightleftharpoons H ^{-}+ OH$
$\triangle H>0$
Increasing temperature will increase equilibrium constant of the above endothermic reaction.
At the mid-point of titration $pH =p K_{a}$.