Question

Give the formula of the complex used in electroplating of object by silver.

• A. $Na\left[Ag\right(H_{2}O{)}_2]CN$
• B. $Na\left[Ag\right(N{H}_3{)}_2]Cl$
• C. $Na\left[AgC{l}_2\right]$
• D. $Na\left[Ag\right(CN{)}_2]$

Answer 1

The correct option is D $Na\left[Ag\right(CN{)}_2]$

In silver plating, the object to be plated (e.g., a spoon) is made from the cathode of an electrolytic cell. The anode is a bar of silver metal, and the electrolyte (the liquid in between the electrodes) is a solution of silver cyanide, AgCN, in water. When a direct current is passed through the cell, positive silver ions ($A{g}^{+}$) from the silver cyanide migrate to the negative anode (the spoon), where they are neutralized by electrons and stick to the spoon as silver metal:
Meanwhile, the silver anode bar gives up electrons to become silver ions:
Thus, the anode bar gradually dissolves to replenish the silver ions in the solution. The net result is that silver metal has been transferred from the anode to the cathode, in this case the spoon. This process continues until the desired coating thickness is built up on the spoon-usually only a few thousandths of an inch-or until the silver bar has completely dissolved.
$Na\left[Ag\right(CN{)}_2]$ is used in this process.