Chemical And Ionic Equilibrium Result Question 39
39. Which of the following statement(s) is (are) correct?
(1998, 2M)
(a) The pH of $1.0 \times 10^{-8} \mathrm{M}$ solution of HCl is $8$
(b) The conjugate base of $\mathrm{H}_2 \mathrm{PO}_4^{-}$ is $\mathrm{HPO}_4^{2-}$
(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 $ \mathrm{pH}=\left(\frac{1}{2}\right) \mathrm{p} K_a $
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Answer:
Correct Answer: 39. ( b,c )
Solution:
- $\mathrm{pH}$ of $10^{-8} \mathrm{M}$ solution will be between $6$ and $7$ but never $8$ . The conjugate base of an acid is formed by removing a proton $\left(\mathrm{H}^{+}\right)$ from acid. Therefore, $\mathrm{HPO} _4^{2-}$ is a conjugate base of $\mathrm{H} _2 \mathrm{PO}^{-} _4$.
$ \mathrm{H} _2 \mathrm{O} \rightleftharpoons \mathrm{H}^{+}+\mathrm{OH}^{-} $ $\quad \quad \quad\quad\Delta H > 0$
Increasing temperature will increase equilibrium constant of the above endothermic reaction.
At the mid-point of titration $\mathrm{pH}=\mathrm{p} K _a$
BETA
