Question

What is the difference between iron and aluminium with respect to corrosion?
a.) Aluminium does not corrode.
b.) The corroded iron is soluble.
c.) Iron does not corrode.
d.) Aluminium is less reactive than iron and corrodes less.

Answer 1

Hint: Iron is more reactive metal than aluminium and corrosion of iron is called rusting.
- Aluminium alloy is widely used for aerospace purposes instead of iron alloy.

Complete Solution :
Corrosion and rusting are the chemical processes which occur in the surface of the metal when it is exposed to its natural environment. When a metal comes to the exposure of air, water and moisture, over a time period it starts degenerating and breaks into small particles this process is known as corrosion.
When the metal is exposed to an external environment, it gets oxidized by the oxygen in the environment.
A metal in which corrosion takes place behaves like either cathode or anode. The exposed metal releases electrons to the oxygen and behave like anode.
Some metals are resistant to corrosion while some metal are prone to corrosion depending on the activity of the metal.
(A) Aluminium reacts with oxygen and gets corroded.
(B) The corroded iron is called rust, which is insoluble. It deposited on the surface of metal.
(C) Iron easily reacts with oxygen and gets corroded.
     \[\begin{align}
 & 4F{{e}_{2}}\,+{{O}_{2}}\,\,\to 4F{{e}^{3+}}\,+\,\,2O_{2}^{-} \\
 & F{{e}^{2+\,}}\,+\,2{{H}_{2}}O\,\,\rightleftarrows \,Fe{{(OH)}_{2}}\,+\,2{{H}^{+}} \\
\end{align}\]\[\begin{align}
 & 4F{{e}_{2}}\,+{{O}_{2}}\,\,\to 4F{{e}^{3+}}\,+\,\,2O_{2}^{-} \\
 & F{{e}^{2+\,}}\,+\,2{{H}_{2}}O\,\,\rightleftarrows \,Fe{{(OH)}_{2}}\,+\,2{{H}^{+}} \\
\end{align}\]

(D) $\text{Al}$ Iron easily reacts with the environment and gets corroded but when $\text{Al}$ (aluminium) reacts with oxygen it forms $\text{A}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}}$ (aluminium oxide) on the surface of the metal and it forms a protective covering on the surface of the metal which prevents the further corrosion of aluminium metal compared to the iron.
So, the correct answer is “Option A”.

Note: Rusted iron gets removed and shed off, so the lower surface comes in direct contact with the environment and that results in further corrosion.
- Corrosion is simply meant to form a layer of metal oxide on the surface.