Question

A student puts one big iron nail each in four test tubes containing solutions of zinc sulphate, aluminium sulphate, copper sulphate and iron sulphate. A reddish-brown coating was observed only on the surface of iron nail which was put in the solution of

• A. zinc sulphate
• B. iron sulphate
• C. copper sulphate
• D. aluminium sulphate

Answer 1

The correct option is C

copper sulphate

• Arrangement of the metals on the basis of their reactivity towards other elements is termed as activity series. Elements at the top of this series are comparatively more reactive than elements below in the series.
• In a single displacement reaction, an element from its compound is substituted by another element to form two product molecules. Metals present above in the activity series can displace the metal present below it in the series.
• Since Iron $\left(\mathrm{Fe}\right)$ is present above Copper $\left(\mathrm{Cu}\right)$ in the activity series, Iron $\left(\mathrm{Fe}\right)$ displaces Copper from Copper sulfate $\left({\mathrm{CuSO}}_4\right)$ to form Iron(II) sulfate $\left({\mathrm{FeSO}}_4\right)$ and Copper.

$\mathrm{Fe}\left(\mathrm{s}\right)+{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)\to {\mathrm{FeSO}}_4\left(\mathrm{aq}\right)+\mathrm{Cu}\left(\mathrm{s}\right)$

• Due to the formation of Copper $\left(\mathrm{Cu}\right)$, the coating of reddish-brown color is noticed on Iron nails.

• Since Zinc $\left(\mathrm{Zn}\right)$ is present above Iron in the activity series, Iron $\left(\mathrm{Fe}\right)$ cannot displace Zinc from Zinc sulfate $\left({\mathrm{ZnSO}}_4\right)$.
• Hence, the reaction will not occur in this case.
• Since Iron cannot displace Iron from Iron (II) sulfate, the reaction will not occur.
• Since Aluminium $\left(\mathrm{Al}\right)$ is present above Iron in the activity series, Iron $\left(\mathrm{Fe}\right)$ cannot displace Aluminium from Aluminium sulfate $\left({\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3\right)$.
• Hence, the reaction will not occur in this case.

Hence, option C is correct. A reddish-brown coating was observed in the case of Copper sulfate.