Question

For gold plating on a copper chain, the substance required in the form of solution is
A. Copper sulphate
B. Copper chloride
C. Potassium cyanide
D. Potassium aurocyanide

Answer 1

Hint: Gold-plating is a type of electroplating. To answer this question, we need to determine which solution shows maximum efficiency, in terms of the deposit of gold.

Complete Step by Step Answer:
Gold-plating can be defined as the process of coating metal objects by electrolytic deposition of gold over them. In electroplating, there is partial melting of metals that results in the chemical bonding of metals with the use of electric current.

According to the question, we have to plate gold on a copper chain. That means we can not take any solution (electrolyte) having copper in them as it would decrease the reactivity rate. So copper sulphate and copper chloride could not be used.

Out of potassium cyanide and potassium aurocyanide, in gold-plating industries, potassium aurocyanide is most commonly used. Its main reason is that potassium aurocyanide (or potassium gold cyanide) provides maximum efficiency in terms of deposited gold.

The solution of potassium gold cyanide is made from potassium cyanide and gold chloride in a bath of heated electrolyzed water, and is also known to provide more pure coverage of gold than the other methods which use aqua regia (known for its ability to dissolve gold).

The correct option is D.

Additional information: As the metals are bonded chemically during electroplating, they don’t flake off, but can wear away or rub off over time. The use of potassium aurocyanide is very restrictive and should be done under the supervision of an experienced person due to its highly toxic nature.

Note: Just like gold, other metals can also be deposited on any other metal by electroplating to prevent corrosion and rusting. This is also done to make objects look more attractive with the lustre of the electroplated metal.