The aqueous solution of $ZnSO_4, AgNO_3, FeCl_3$ and $WCl_6$ are electrolyzed for 2 hours using a current of 5 amperes. The decreasing order of mass deposited of the following metals at cathode will be.........
(A) Zn
(B) Ag
(C) Fe
(D) W
(atomic mass: $Fe =56\, g\, mol^{-1}, Zn =65\, g\, mol^{-1}, Ag = 108\, g\, mol^{-1}, W = 184\, g\, mol^{-1}$)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (B), (A), (D), (C)
From Faraday’s Law: Mass deposited ∝ Equivalent weight
Equivalent weight = Atomic mass / Valency
At cathode:
Ag⁺ → Ag (valency = 1)
Zn²⁺ → Zn (valency = 2)
Fe³⁺ → Fe (valency = 3)
W⁶⁺ → W (valency = 6)
Calculate equivalent weights: Atomic mass / Valency
- Zn: 65 / 2 = 32.5
- Ag: 108 / 1 = 108
- Fe: 56 / 3 ≈ 18.67
- W: 184 / 6 ≈ 30.67
Mass deposited ∝ M/n, so decreasing order:
$\text{Ag > Zn > W > Fe}$
(B), (A), (D), (C)