Paper: CSIR-NET December 2019 · Subject: Physical Chemistry · Chapter: Electrochemistry · Topic: Electrochemistry – General · Marks: 2 · Difficulty: Medium
An aqueous solution contains $0.02 \mathrm{mol} \mathrm{kg}^{-1} \mathrm{NaCl}$ and $0.03 \mathrm{mol} \mathrm{kg}^{-1} \mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}$. The logarithm of mean ionic activity coefficient $\left(\log \gamma_{ \pm}\right)$of this solution at 25°C is
(a)$-\sqrt{0.095}$
(b)$\sqrt{0.154}$
(c)$-\sqrt{0.033}$
(d)$-\sqrt{0.11}$
Answer
Answer: D ✓ checked by 4AB · confidence low
Explanation
I = ½Σmz² = ½(0.02 + 0.02 + 0.03 × 4 + 0.06) = 0.11. The intended limiting-law answer is log γ± ∝ −√I = −√0.11 (d), with the A|z₊z₋| factor ignored for the mixture.