The rusting of iron nail

Rusting is a chemical process where iron (Fe) reacts with oxygen (O2) and moisture (H2O) from the atmosphere to form hydrated iron(III) oxide, commonly known as rust [c1][t1]. The chemical reaction is represented as 4Fe + 3O2 + 6H2O → 2(Fe2O3·3H2O) [t1]. During this process, iron atoms are oxidized, losing electrons to oxygen atoms [t1][t6]. Because the oxygen and water molecules from the air chemically bond with the iron atoms to form the new compound, the total mass of the rusted object increases compared to the original iron nail [t4][t5]. While the rust layer is porous and may eventually flake off, the immediate chemical transformation of iron into iron oxide results in a weight gain due to the addition of oxygen and hydrogen atoms to the solid structure [t2][t4][t9].

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 5: Changes Around Us: Physical and Chemical > 5.3.1 Rusting > p. 62