Question

A student added a piece of zinc metal to four test tubes I, II, III and IV which respectively contain an aqueous solution of aluminium sulphate, zinc sulphate, ferrous sulphate and copper sulphate. In which solution, he observed that the reaction has taken place.

• A. (I), (II)
• B. (II), (III)
• C. (III), (IV)
• D. (I),(IV)

Answer 1

The correct option is C

(III), (IV)

The explanation for the correct option:-

(C) Ferrous sulphate, Copper sulphate

We are aware that the more reactive metal can easily displace a less reactive metal and the process is called displacement. So,

Zn reacts with copper sulphate(${\mathrm{CuSO}}_4$) and ferrous sulphate(${\mathrm{FeSO}}_4$) because:-

1. Zinc is more reactive than copper hence displaces Cu from CuSO₄.
2. Zinc is more reactive than iron hence displaces Fe from FeSO₄.

Reactions:-

1. $\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)$$\to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)$$+\mathrm{Cu}\left(\mathrm{s}\right);\mathrm{Zn}>\mathrm{Cu}$
2. $\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{FeSO}}_4\left(\mathrm{aq}\right)$$\to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)$$+\mathrm{Fe}\left(\mathrm{s}\right):\mathrm{Zn}>\mathrm{Fe}$

The explanation for the incorrect answer:-

Option (A)

1. Zinc is less reactive than Aluminium according to reactivity series.
2. Zinc doesn't react with Zinc itself.

$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{Al}}_2$$({\mathrm{SO}}_4$${)}_3$$\left(\mathrm{aq}\right)\to \mathrm{No}\mathrm{reaction}$

$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{ZnSO}}_4$$\left(\mathrm{aq}\right)\to \mathrm{No}\mathrm{reaction}$

Option (B)

1. Zinc doesn't react with Zinc itself.

$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)\to \mathrm{No}\mathrm{reaction}$

Option (D)

1. Zinc is less reactive than Aluminium according to reactivity series.

$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3\left(\mathrm{aq}\right)\to \mathrm{No}\mathrm{reaction}$

Hence, the correct option is (C).