Question

When iron nails are added to an aqueous solution of copper sulfate, a chemical change occurs, which of the following is not true about this reaction?
(A) Blue color of the solution fades
(B) Iron nails become brownish in color
(C) It is a displacement reaction
(D) Iron nails dissolve completely

Answer 1

Iron nails are made up of iron metal only. As copper sulfate is blue colored salt, its aqueous solution will also be blue in color. More reactive metal can displace the less reactive metal in its solution.

Complete step by step answer:
Let’s first see which and what type of chemical change will occur as iron nails will react with an aqueous solution of copper sulfate.
- Iron nails are made up of iron metal. So, iron metal will react with copper sulfate to give ferrous sulfate and copper metal. The reaction can be given as under.
$F{e_{(s)}} + CuS{O_{4(aq)}} \to FeS{O_{4(aq)}} + C{u_{(s)}}$
- Here displacement of copper from copper sulfate solution is done by iron, so it is a kind of a displacement reaction. So, option (C) is a true sentence.
- In Displacement reaction, the more reactive metal always replaces the less reactive metal from its solution. This reaction is occurring here. We can also explain this reaction by oxidation potential of these both metals. Oxidation potential of iron metal is 0.44V and oxidation potential of Cu metal is (-0.34)V , hence iron will get oxidized and copper will get reduced when both will react.
- Now copper sulfate is a blue coloured salt and hence the aqueous solution of copper sulfate will also be blue in colour. Now, as the reaction will proceed, the concentration of copper sulfate in the solution will gradually decrease and hence the blue color of the solution of the solution will also fade as the reaction will proceed. So, the statement in option (A) is also correct.
- As the reaction will complete, all the iron metal from the solution will get converted into ferrous sulfate solution, so no iron nails will be there. So, we can say that option (D) is also a correct statement.
- Color of iron nails will not change in this reaction. So, the statement in option (B) is not correct.

So, the correct answer is “Option (B) Iron nails become brownish in color”.

Note:

Remember that iron nails getting brownish color is the corrosion of iron and corrosion is not occurring here. If less reactive metal is allowed to react with solution of more reactive metal, then displacement reaction will not occur.