4AB › Chemistry PYQ › CSIR-NET › December 2014 › Q26Q26 · CSIR-NET Chemistry, December 2014 Paper: CSIR-NET December 2014 · Subject: Physical Chemistry · Chapter: Chemical Kinetics · Topic: Rate Laws Order · Marks: 2 · Difficulty: Medium
The rate constant for a reaction $A^{+}+B^{n+1} \rightarrow P$ is measured in two different aqueous solutions of ionic strengths $0.01\,\mathrm{M}$ and $0.04\,\mathrm{M}$. If $\log\dfrac{K_{0.04}}{K_{0.01}}=0.3$, the charge $n$ on B is closest to
Answer Answer: C ✓ checked by 4AB · confidence high
Explanation Primary salt effect (Debye–Hückel): log(k/k₀) = 2(0.509) z_A z_B √I, so log(k₀.₀₄/k₀.₀₁) = 1.018 z_A z_B (√0.04 − √0.01) = 0.1018 z_A z_B.
0.1018 z_A z_B = 0.3, so z_A z_B ≈ 2.95 ≈ 3. With z_A = +1, the charge on B is +3.
The question defines n as the charge on B, so the superscript printed as 'n+1' is to be read as Bⁿ⁺. Then n = 3. Answer (c).
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