JEE PYQ: Ionic Equilibrium Question 23
Question 23 - 2019 (10 Apr Shift 1)
Type: MCQ
Consider the following statements:
(a) The pH of a mixture containing 400 mL of 0.1 M $\text{H}_2\text{SO}_4$ and 400 mL of 0.1 M NaOH will be approximately 1.3.
(b) Ionic product of water is temperature dependent.
(c) A monobasic acid with $K_a = 10^{-5}$ has a pH $= 5$. The degree of dissociation of this acid is 50%.
(d) The Le Chatelier’s principle is not applicable to common-ion effect.
The correct statements are:
(a) (a), (b), and (d)
(b) (a), (b) and (c)
(c) (b) and (c)
(d) (a) and (b)
Show Answer
Answer: (a)
Solution
(a) $\text{H}_2\text{SO}_4$: 0.04 mol $\text{H}^+$ from first dissociation = 0.08 mol total. NaOH: 0.04 mol. Remaining $\text{H}^+$ after neutralization: $[\text{H}^+] = \frac{0.04}{0.80} = 0.05$ M; pH $= 1.3$ ✓
(b) Ionic product of water increases with temperature because ionisation of water is endothermic. ✓
(c) $K_a = \frac{C\alpha^2}{1-\alpha}$; pH $= 5 \Rightarrow [\text{H}^+] = 10^{-5}$
$K_a = 10^{-5} = \frac{C\alpha}{1-\alpha} \cdot \frac{\alpha}{1} \Rightarrow C\alpha = 10^{-5}$, and $\alpha = \frac{1}{2}$, i.e., 50% ✓
(d) Le Chatelier’s principle IS applicable to common-ion effect. ✗
BETA
