Question

A copper coin was electroplated with $Zn$ and then heated at a high temperature until there is a change in colour what will be the resulting colour?
(A) White
(B) Black
(C) Silver
(D) Golden

Answer 1

Hint: Try to recall that zinc is used for electroplating and when a copper coin is electroplated with zinc and heated at high temperature, then it forms an alloy of brass. Now, by using this you can easily find the correct option from the given ones.

Complete step by step solution:
-First, let us look at the definition of electroplating before we move on to check what happens when a copper coin is electroplated with zinc.
-Electroplating is done by the electrodeposition process using 2 electrodes. The material that is to be electroplated acts as one of the electrodes and the material gets deposited on its surface as the reaction continues in the cell. It usually involves the application of one metal on the surface of another metal to prevent processes like corrosion from happening.
-We know that electroplating of copper coin with zinc is done by running a current through a solution in which copper coin is dipped into a solution of sodium zincate in contact with zinc metal.
-By running a current through an electrochemical cell with a copper coin as anode and zinc as the cathode and both copper and zinc must be in contact, either directly or by means of a wire.
-When current is passed through an electrochemical cell, then copper gets oxidised at anode and the electrons released by it combine with dissolved zinc in a process called reduction. The half cell reactions are:
\[\begin{align}
& Cu\to Cu+2{{e}^{-}}\text{ (Anode)} \\
& Zn+2{{e}^{-}}\to Zn\text{ (Cathode)} \\
\end{align}\]
-As dissolved zinc reduces to metallic zinc, $Zn$, it precipitates out of solution and since copper is the source of electrons, the zinc touching copper coin will turn solid first, plating the copper coin.
-The coating of the copper coin with zinc appears silver in colour and when the plated coin is heated at high temperature, then zinc migrates into the surface layer of copper and forms an alloy of brass which gives a gold appearance to the coin.

Therefore, from above we can conclude that option D is the correct option to the given question.

Note: Brass is paired alloy made out of copper and zinc-containing copper about 60% and 40% of zinc and is used for making utensils, condenser tubes, etc. Also, you should remember that the zinc plating process is used industrially with cyanide ions as the complexing agent.