Question

A 4.0 molar aqueous solution of NaCl is prepared and 500 mL of this solution is electrolysed. This leads to the evolution of chlorine gas at one of the electrode.

[Atomic mass: Na = 23, Hg = 200; 1 Faraday = 96500 coulombs]

If the cathode is a Hg electrode, the maximum weight (g) of amalgam formed from this solution is:

• A. 200
• B. 225
• C. 400
• D. 446

Answer 1

The correct option is D 446

When Hg is used as the cathode, Na+ will be reduced to form sodium amalgam, Na-Hg.

At cathode: $N{a}^{+}+1e^{-}+Hg\to Na-Hg$

2.0 moles of NaCl present in the solution contains 2 moles of Na+ in 0.5 liters of 4 M solution. Hence two moles of Na-Hg are formed.

The mass of 2 moles of Na-Hg = 2 (23 + 200) = 446 g.