Question

When zinc granules are added to copper sulfate……… is deposited at the bottom?
A. Copper
B. Zinc
C. Sulfur
D. Oxygen

Answer 1

Hint: To answer this question you should know that the standard reduction potential of zinc is less than copper. Now you can definitely mark the correct option.

Complete step by step answer:
First, let’s look at the Standard reduction potential value of both,

$Zn^{ 2+ }(aq)\quad +\quad 2e^{ - }\quad \rightarrow \quad Zn(s)$ (Standard reduction potential = -0.76)
$Cu^{ 2+ }(aq)\quad +\quad 2e^{ - }\quad \rightarrow \quad Cu(s)$ (Standard reduction potential = 0.34)

The standard reduction potential of zinc is negative, hence it is more reactive than copper which has a positive value of standard reduction potential.
Thus when zinc granules are added to the solution of copper sulfate, zinc displaces copper to form zinc sulfate and thus copper gets deposited.
$CuSO_{ 4 }$ + Zn $\rightarrow$ $ZnSO_{ 4 }$ + Cu

In this reaction, zinc metal can easily displace the copper metal from its salt to form an aqueous solution of zinc sulfate. Hence, This reaction is also an example of a displacement reaction.

Therefore, we can conclude that the correct answer to this question is option A.

Note: Here we can also observe that the copper sulfate solution is blue in color. But when Zinc granules are kept in copper sulfate solution the blue color of the copper sulfate solution turns colorless. The reason for this we have already discussed (because the zinc is more reactive than the copper metal in the reactivity series).