Question

A silver-grey coloured rod is placed in a blue solution. The blue colour of the solution fades away gradually and after a few days, the rod appears etched. Answer the following:
A.Name the silver-grey material of the rod.
B.Name and write the formula of the substance present in the blue solution.
C.Write the chemical equation for the reaction involved?
D.What type of reaction?

Answer 1

Hint:Copper salts are generally blue in colour and the copper ions are reduced to copper atoms by the silver-grey substance and hence the colour fades away after a few days. Generally those metals can reduce the copper from the copper solution which is placed about it in the electrochemical series.

Complete answer:
A.The silver coloured rod that was placed in the blue coloured solution was that of Iron. The metallic iron is placed above copper in the electrochemical series and its reduction potential is less than that of copper and hence it displaces the copper from the copper sulphate solution which is present in the blue-coloured solution. Hence,
The silver-grey material of the rod is “metallic iron”.
B.The name of the substance present in the blue-coloured solution is “copper sulphate pentahydrate” and its formula is$\text{CuS}{{\text{O}}_{\text{4}}}\text{.5}{{\text{H}}_{\text{2}}}\text{O}$. The anhydrous salt, i.e., copper sulphate is white in colour and when it gets hydrated then it attains that blue colour.
C.The chemical equation involved in the reaction is as follows:
$\text{Fe }\left( \text{s} \right)\text{+ CuS}{{\text{O}}_{\text{4}}}\left( \text{aq} \right)\to \text{FeS}{{\text{O}}_{\text{4}}}\left( \text{aq} \right)\text{+ Cu}\downarrow $
D.This type of reaction is termed as “displacement reaction” in which the metal which has higher tendency to get oxidized loses its electrons to the metal that has higher tendency to get reduced so that it gets discharged as metallic atoms in the solution.

Note:
The electrochemical series of the elements consists of the elements arranged in a series depending on the reduction potential of the elements. The ones which have a high tendency to get reduced are placed at the bottom while those which have a high tendency to get oxidised are placed at the top.