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Coordination Compounds
Applications of Coordination Compounds: Electroplating
1 question from 1 paper, each with its answer.
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Concepts tested
- Complex ion in electroplating
All Questions
2002 AIPMT 1 question
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In the silver plating of copper, $K[Ag(CN)_2]$ is used instead of $AgNO_3$. The reason is : -Copper is more reactive than silver. With $AgNO_3$ solution, copper would directly displace silver: $Cu + 2Ag^+ \rightarrow Cu^{2+} + 2Ag$. This gives a loose, uneven deposit instead of a smooth plating.
In $K[Ag(CN)_2]$, silver is held in the stable complex ion $[Ag(CN)_2]^-$, so the concentration of free $Ag^+$ ions is very low.
Copper cannot displace silver from this complex, and $Ag^+$ is supplied slowly during electrolysis. This gives a smooth, even and firmly adhering coating.
So $K[Ag(CN)_2]$ is used because of less availability of $Ag^+$ ions, as Cu cannot displace Ag from the $[Ag(CN)_2]^-$ ion.