Paper: CSIR-NET June 2019 · Subject: Physical Chemistry · Chapter: Electrochemistry · Topic: Electrochemistry – General · Marks: 2 · Difficulty: Medium
The mobility of a divalent cation in water is $8 \times 10^{-8} \mathrm{m}^{2} \mathrm{V}^{-1} \mathrm{S}^{-1}$. The effective radius of the ion is (viscosity of water $=1 \mathrm{cP} ; \mathrm{e}=1.6 \times 10^{-19} \mathrm{C}$ )
(a)106 pm
(b)212 pm
(c)424 pm
(d)318 pm
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
Stokes: r = ze/(6πηu) = 2 × 1.6×10⁻¹⁹/(6π × 10⁻³ × 8×10⁻⁸) = 2.1×10⁻¹⁰ m = 212 pm.