The aqueous solutions of the following salts were electrolyzed for 30 min with a current of 20 amp. Arrange the following in the increasing order of the amount of metal deposited at the cathode.
$ \text{(A) }\mathrm{WCl}_6 $
$ \text{(B) }\mathrm{ZnSO}_4 $
$ \text{(C) }\mathrm{HfCl}_4 $
$ \text{(D) }\mathrm{AgNO}_3 $
(Atomic mass of: W =184 μ, Zn = 65 μ, Hf = 178 μ and Ag = 108 μ)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B), (C), (D)
The amount of metal deposited at the cathode is proportional to the equivalent weight of the metal when the same current and time are used.
Reasoning:
By Faraday’s second law, for equal charge passed:
Amount deposited ∝ Equivalent weight = Atomic mass / Valency
Calculate for each salt:
(A) WCl₆ → W⁶⁺
Equivalent weight = 184 / 6 = 30.67
(B) ZnSO₄ → Zn²⁺
Equivalent weight = 65 / 2 = 32.5
(C) HfCl₄ → Hf⁴⁺
Equivalent weight = 178 / 4 = 44.5
(D) AgNO₃ → Ag⁺
Equivalent weight = 108 / 1 = 108
Increasing order of deposition (lowest to highest):
WCl₆ < ZnSO₄ < HfCl₄ < AgNO₃
Therefore, the order is:
(A), (B), (C), (D)