Question

Assertion: Zinc replaces copper from copper sulphate solution.
Reason: The \[{E^0}\] of zinc is \[ - 0.76V\] and that of copper is \[ + 0.34V\].
A. Both assertion and reason are correct and reason is the correct explanation for assertion.
B. Both assertion and reason are correct and reason is the correct explanation for assertion.
C. Assertion is correct but reason is incorrect.
D. Both assertion and reason are incorrect.

Answer 1

Hint: Electrode potential is the tendency of an electrode to lose or gain an electron when it contacts with its own ions in a solution. Similarly, the reduction potential is the tendency to get reduced. The greater the negative value of the reduction potential value in the electrochemical series, the greater will be the tendency to act as a reducing agent.

Complete step by step answer:
On comparing the standard electrode potential of zinc and copper, zinc has negative electrode potential whereas copper has positive electrode potential. Generally, the greater the negative value of the reduction potential value in the electrochemical series, the greater will be the tendency to act as a reducing agent.
Thus, zinc acts as a good reducing agent than copper. This implies that zinc can reduce copper by changing its oxidation number from \[[ + 2 \to 0]\]
The reducing agent is the one that reduces other elements thereby oxidizing on its own. So zinc will undergo oxidation and give up two electrons.
The reaction can be written as,
\[Zn \to Z{n^{2 + }} + 2{e^ - }\]
The liberated two electrons from zinc will now be added to copper ions forming copper metal.
 \[C{u^{2 + }} + 2{e^ - } \to Cu\]
The overall reaction can be written as,
\[Zn + C{u^{2 + }} \to Z{n^{2 + }} + Cu\]
\[Zn + CuS{O_4} \to ZnS{O_4} + Cu\]
Thus, zinc can replace copper from copper sulphate solution. The reverse process won't be possible because copper is less reactive than zinc and also the standard reduction potential of copper is positive.

Therefore, both assertion and reason are correct and reason is the correct explanation for assertion (B).

Note: Reducing agent helps to reduce the other compounds thereby oxidize on its own. So, reducing agent is mainly used in the reduction process. Here, zinc sulphate acts as a reducing agent and thus, it replaces copper from copper sulphate solution by the reduction of copper sulphate to copper metal. \[C{u^{2 + }}( + 2) \to Cu(0)\].