Question

One faraday of electricity will liberate one gram-atom of the metal form a

solution of
(A)AuCl3 (B) BaCl2 (C) CuSO4 (D) NaCl

Answer 1

The answer is D) NaCl

One faraday is equivalent to one mol of electrons and the sodium ion (
`Na^+`) is the only metallic ion with a value of oxidation number equal to (1+).

Is there any mistake in my English? Please let me know.

Answer 2

Answer: D) NaCl

Explanation: In given answer choices the metals are Au, Ba, Cu and Na. Cl has -1 charge and sulfate ion has -2 charge.

Since there are three Cl atoms for each Au, the charge on Au is +3. Similarly, the charge on Ba is +2, charge on Na is +1. There is one sulfate ion for each Cu and so the charge on Cu is +2.

In electrolysis, the metals are deposited when they are reduced on accepting electrons. The half equations for all the above four metals are written as:

`Au^+^3(aq)+3e^-\rightarrow Au(s)`

`Ba^+^2(aq)+2e^-\rightarrow Ba(s)`

`Cu^+^2(aq)+2e^-\rightarrow Cu(s)`

`Na^+(aq)+1e^-\rightarrow Na(s)`

Looking at all the four equations, it's only the last equation that involves one electron. So, one faraday of electricity will liberate one gram-atom of sodium metal from a solution of NaCl.