Question

Which of the following metal is used for galvanising iron to protect it from rusting?
(A) \[Al\]
(B) \[Cu\]
(C) \[Co\]
(D) \[Zn\]

Answer 1

Hint: It is a debated transition element, metallic in nature. It belongs to the group of cadmium and mercury and has \[[Ar](n-1){{d}^{10}}n{{s}^{2}}\]configuration. It is also considered to be one of the 14 essential trace elements found in the human body.

Complete step by step answer:
The process of applying a coating of zinc (\[Zn\]) on iron or steel to protect it from rusting is called galvanising or galvanizing iron.
Rusting of iron is an oxidation reaction. So to prevent it from rusting, a more reactive metal should be used that will prevent iron from losing its electrons and becoming oxidized when kept open in the air.
These metals are called sacrificial metals.
Examples are zinc (\[Zn\]) and magnesium (\[Mg\]).
Zinc is more reactive than iron, so zinc will react preferentially.
The reaction of iron with air and water results in rusting:
Anode: \[Fe\left( s \right)~\to F{{e}^{2+}}\left( aq \right)\text{ }+\text{ }2{{e}^{-}}\]
Cathode: \[{{O}_{2}}\left( g \right)\text{ }+\text{ }4{{H}^{+}}\left( aq \right)\text{ }+\text{ }4{{e}^{-}}~\to ~2{{H}_{2}}O\left( l \right)\]
\[F{{e}^{2+}}\]is oxidized to \[F{{e}^{3+}}\]as follows:
\[4Fe\text{ }+\text{ }3{{O}_{2}}\text{ }\to \text{ }2F{{e}_{2}}{{O}_{3}}\]
 Rust deposits as\[F{{e}_{2}}{{O}_{3}}.x{{H}_{2}}O\].
The reaction of iron(III) oxide with zinc is as follows:
\[F{{e}_{2}}{{O}_{3}}\text{ }+\text{ }3Zn\to \text{ }3ZnO\text{ }+\text{ }2Fe\]
Here, zinc serves as anode and iron as the cathode.
So, the correct option is D.

Note: Zinc is also called sacrificial anode. The process is called cathodic protection. If zinc is scratched or corroded, it will continue to protect the iron from oxidation electrochemically. Tin also protects iron from rusting. But when it is worn away, it accelerates rusting instead of protecting it.