Question

How will the mass of a rusted iron nail compare with the mass of the same nail before it rusted$?$

Answer 1

Rusting of iron refers to the formation of a mixture of iron oxides, on the surface of iron objects or structures commonly known as rust. The rust is formed by a redox reaction between ${O_2}$ and $Fe$ in an environment containing water such as air which has high levels of moisture.

Complete step-by-step answer: The rusting of iron is characterized by the formation of a mixture of iron oxides which are present as a layer of red, flaky substance that easily crumbles into a powder.
The exposure of $Fe$ or any alloy of iron to ${O_2}$ in the presence of moisture leads to the formation of rust. This reaction is not instantaneous, and it generally takes place over a large time frame. The ${O_2}$ atoms bond with $Fe$ atoms, resulting in the formation of the iron oxides. This results in weakening of the bonds between the $Fe$ atoms in the compound.
The reaction of the rusting of iron involves loss of electrons which results in an increase in the oxidation state of iron. Rust is generally made up of two different oxides of iron that vary in the oxidation state of the $Fe$ atoms in their oxides. These oxides are: $Fe\left( {II} \right)$ oxide i.e. $FeO$ where the oxidation state of $Fe$ is $+ 2$ and $Fe\left( {III} \right)$oxide or $F{e_2}{O_3}$, where the $Fe$ atom exhibits an oxidation state of $+ 3$. The overall chemical equation can be represented as:
$F{e^{ + 2}} + 2F{e^{ + 3}} + 8O{H^ - } \to F{e_3}{O_4} + 4{H_2}O$, where $F{e_3}{O_4}$is generally referred to as the rust.
Due to the process of rusting, $Fe$ is gaining ${O_2}$, and the initial amount of $Fe$ of the rust free nail remains resulting in an increase in weight of the rusted iron nail. So the mass of the rusted iron nail is more than that of the rust free iron nail.

Note: Rusting of iron is a great example of the corrosion of metals, where the surfaces of metals are degraded into chemically more stable oxides. However, in general the term rusting is used to refer to the corrosion of objects made of iron or alloys of iron only.