Question

Aluminium is used in thermite welding because

• A. It is a strong oxidizing agent
• B. It is a reactive metal
• C. It is a light metal
• D. It has more affinity for oxygen

Answer 1

The correct option is D

It has more affinity for oxygen

• Thermite reaction: Thermite reaction is an exothermic oxidation-reduction (redox) reaction in which iron oxide $\left({\mathrm{Fe}}_2{\mathrm{O}}_3\right)$ reacts with aluminium $\left(\mathrm{Al}\right)$ powder to produce molten iron and aluminium oxide $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$ and a large amount of heat.
• Aluminium is used in thermite reactions because it is a strong reducing agent and hence it has more affinity for oxygen.

$$\begin{gathered} {\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+\mathrm{Al}\left(\mathrm{s}\right)\stackrel{}{\to }\mathrm{Fe}\left(\mathrm{l}\right)+{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+\mathrm{Heat} \\ (\mathrm{Ferric}\mathrm{oxide})\left(\mathrm{Aluminium}\right)\left(\mathrm{Iron}\right)(\mathrm{Aluminium}\mathrm{oxide}) \end{gathered}$$

• In thermite reaction, solid ferrous oxide gets reduced to molten iron and the aluminium powder gets oxidized to aluminium oxide.

The explanation for the incorrect option:

Option A:
Oxidising agent:

An oxidizing agent is a compound or element that participates in a redox (oxidation-reduction) reaction and accepts electrons from a different species.

Aluminium has a strong affinity for oxygen and it is readily oxidised.

Option B:
Aluminium is a reactive metal but it does not react vigorously due to its impenetrable rust layer.

Option C:
Aluminium is a light metal. It is almost three times lighter than iron.

Despite aluminium being strong, tough metal

Hence, the correct option is (D).