Question

What is the chemical formula of rust?

Answer 1

You should know that rust is not a single pure compound. It is basically a mixture of hydrates of iron oxides and iron hydroxides. Now try to figure out the answer by yourself.

Complete step by step answer:
Rust is the general term used for a series of iron oxides which are formed by the reaction of iron with oxygen in the presence of water or moisture.
Rusting is an electro-chemical process. The rate of oxidation of iron occurs more quickly in the presence of some electrolytes like saltwater and other acidic or alkaline substances. In chemistry rusting is generally referred to as oxidation. Oxidation is nothing but a chemical process where metal gains oxygen and becomes oxide.

Any iron (II) salts generated by the cell are likely to be oxidized either electrochemically or by oxygen in the air to make iron (III) salts.
The iron (III) will generally undergo hydrolysis to form hydroxide and oxide containing compounds which are less soluble than simple hydrated iron (II) or iron (III) complexes. These will form the brown rust you generally see on rusty metal surfaces.

The chemical equations for rust formation are;

${ Fe }_{ 2 }+(aq)+2{ OH }^{ - }(aq)Fe(OH)2(s)$

$Fe(OH)2(s)={ O }_{ 2 }=>Fe(OH)3(s)$

${ Fe }_{ 2 }{ O }_{ 3 }$ dehydrates to produce ${ Fe }_{ 2 }{ O }_{ 3 }.n{ H }_{ 2 }O(s)$

Therefore, the chemical formula of rust is ${ Fe }_{ 2 }{ O }_{ 3 }.n{ H }_{ 2 }O(s)$ or rust.

Note: You should know that rusting causes slow degradation of iron and its respective alloys, thus prevention of rusting is necessary. The best way to stop rusting is done by scrapping or brushing the metallic surface using sandpaper.