250 mL of a waste solution obtained from the workshop of a goldsmith contains 0.1 M AgNO3 and 0.1 M AuCl. The solution was electrolyzed at 2V by passing a current of 1A for 15 minutes. The metal/metals electrodeposited will be
[ \(E^0_{Ag^+/Ag} = 0.80\ \mathrm{V}\), \(E^0_{Au^+/Au} = 1.69\ \mathrm{V}\) ]
[ \(E^0_{Ag^+/Ag} = 0.80\ \mathrm{V}\), \(E^0_{Au^+/Au} = 1.69\ \mathrm{V}\) ]
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- Silver and gold in equal mass proportion
- Silver and gold in proportion to their atomic weights
- Only gold
- Only silver
The Correct Option is C
Solution and Explanation
Amount of \(\mathrm{Au^+}\) present: \(0.25\ \mathrm{L}\times 0.1\ \mathrm{M} = 0.025\) mol, which needs 0.025 mol of electrons for complete deposition (more than the 0.0093 mol supplied).
\(\mathrm{Au^+}\) has the higher reduction potential (1.69 V against 0.80 V), so it is reduced first at the cathode and, since it is not exhausted, the cathode potential stays near 1.6 V, far above that needed for \(\mathrm{Ag^+}\). Hence silver does not deposit.
Only gold is deposited.
Answer: (3) Only gold
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