Question

Reaction of iron nail with copper sulfate solution is_____________
A. combination reaction.
B. displacement reaction
C. double displacement reaction
D. decomposition reaction

Answer 1

Hint: Based on reactivity, iron is more reactive than copper. The reaction leads to a change in color of copper sulfate solution. It changes from blue to green. A change in the oxidation state of iron and copper also occurs here. This is also an example of oxidation-reduction reaction.

Complete step by step solution:
Electrochemical series is the way of arranging the elements in the order of their increasing potential values. These potential values of each element are taken with standard hydrogen electrodes as reference. There are two types of elements-electropositive and electronegative elements. With the help of electrochemical series we can tell whether a metal gets replaced by another metal or not.
The electropositive elements have highly positive reduction potential. While the electronegative has a highly negative reduction potential. The elements having more negative reducing potential are more reactive.
Related to the question, when iron nails are reacted with copper sulfate solution, copper gets displaced by iron. From the electrochemical series, it is clear that iron is more reactive than copper since iron has negative reduction potential. When the iron nails are dipped in copper sulfate solution, iron nails get deposited with reddish brown and the blue color of copper sulfate solution changes to light green color. The equation is as given below.
${\text{F}}{{\text{e}}_{\left( {\text{s}} \right)}} + {\text{CuS}}{{\text{O}}_{4\left( {{\text{aq}}} \right)}} \to {\text{FeS}}{{\text{O}}_{4\left( {{\text{aq}}} \right)}} + {\text{C}}{{\text{u}}_{\left( {\text{s}} \right)}}$

Hence the option B is correct.

Additional information:
Electropositive are those which are prone to lose electrons to the solution and electronegative are those which are prone to gain electrons. The reference hydrogen electrode is kept in the middle. Electropositive elements are kept above hydrogen and electronegative are below hydrogen electrodes in the electrochemical series.

Note: The color change is due to the fact that iron reduces copper from its solution. Copper reduced to 0 state and iron oxidized to +2 state. Thus change in the oxidation state has occurred.