Question

Which of the following can undergo a chemical reaction ?
(A) $MgS{O_4}\, + \,Fe$
(B) $ZnS{O_4}\, + \,Fe$
(C) $MgS{O_4}\, + \,Pb$
(D) $CuS{O_4}\, + \,Fe$

Answer 1

Hint: To predict the feasibility of a reaction you need to check the reactivity of elements from the reduction potential. In electrochemical series elements with less negative value cannot reduce the element with a more negative value.

Complete step by step answer:
To displace an element from its solution, the other element has to be more reactive. It means that it should come above that element in the electrochemical series.
In the case of \[MgS{O_4}\] the metal is magnesium and when you dip an iron rod in it, to reduce magnesium, iron needs to be more reactive. Since the reduction potential of magnesium is $ - 2.37V$ and of iron is $ - 0.76$. From this, we can deduce that the reduction potential of iron is less negative than magnesium so it won’t be able to displace magnesium from the \[MgS{O_4}\] solution. As a result of this, the reaction will not proceed further.
In case of \[ZnS{O_4}\] the reduction potential of iron is $ - 0.44V$ and of zinc is $ - 0.76$. From this, we can deduce that the reduction potential of iron is less negative than zinc so it won’t be able to displace zinc from the \[ZnS{O_4}\] solution.
In case of \[MgS{O_4}\] the reduction potential of magnesium is $ - 2.37V$ and of lead is $ - 0.13$. From this, we can deduce that the reduction potential of lead is less negative than magnesium so it won’t be able to displace zinc from the \[MgS{O_4}\] solution. As a result of this, the reaction will proceed further.
In case of \[CuS{O_4}\]the reduction potential of iron is $ - 0.44V$ and of copper is $0.34$. From this, we can deduce that the reduction potential of iron is more negative than copper so it will be able to displace copper from the \[CuS{O_4}\] solution. So, the reaction will proceed further.

Hence, Option (D) is correct.

Note:
When $Fe$ is placed in a \[ZnS{O_4}\] solution no color change is found because no reaction takes place while we place $Fe$ in \[CuS{O_4}\] the solution the color of the solution changes from blue to green because iron displaces copper ions in the solution.