Question

Write the complete chemical reaction of rusting of iron.

Answer 1

Rust are the oxide and hydroxide of iron which are flaky and friable formed due to the attack of oxygen and moist air to the iron articles. It occurs in the presence of water vapour in the atmosphere.

Complete answer:
Corrosion is the process in which metal like iron is attacked by the substances around it such as moisture, acids, etc. Corrosion causes damage to car bodies which are made up of iron, bridges, and ships, iron railing, and to all objects made of metals. For example silver articles turn black when exposed to air due to the attack of sulphur on silver which forms black coating of silver sulphide on silver articles, copper metal turns from shiny brown to green due to attack of carbon dioxide in air which forms copper carbonate coating, iron when exposed to moist air turns to brown flaky substance called rust.
Rusting of iron is defined as the corrosion of iron which forms a reddish brown coat of iron oxide and hydroxide on the surface of an iron article when exposed to moist air due to attack of oxygen present in air in presence of water.
The chemical reaction of rusting is as follow as:
Being metal, iron tends to lose electrons and also this is accelerated in the presence of oxygen which is an oxidizing agent which tends to oxidize the other at the cost of reducing itself. Water behaves as a catalyst and presence of water is crucial and presence of salt can accelerate the reaction.
$2{\text{Fe}} \to 2{\text{F}}{{\text{e}}^{ + 2}} + 4{{\text{e}}^ - }$
${{\text{O}}_2} + 4{{\text{e}}^ - } + 2{{\text{H}}_2}{\text{O}} \to 4{\text{O}}{{\text{H}}^ - }$
The following redox reaction is crucial and too proceeds in the presence of water. The reaction includes further oxidation of iron from $+ 2$ oxidation state to $+ 3$ oxidation state. The reaction is: $4{\text{F}}{{\text{e}}^{ + 2}} + {{\text{O}}_2} \to 4{\text{F}}{{\text{e}}^{ + 3}} + 2{{\text{O}}^{ - 2}}$
Finally, acid base reactions and dehydration reactions form the oxide and hydroxide of iron, thereby producing rust. The reactions are:
${\text{F}}{{\text{e}}^{ + 2}} + 2{{\text{H}}_2}{\text{O}} \rightleftharpoons {\text{Fe}}{\left( {{\text{OH}}} \right)_2} + 2{{\text{H}}^ + }$
${\text{F}}{{\text{e}}^{ + 3}} + 3{{\text{H}}_2}{\text{O}} \rightleftharpoons {\text{Fe}}{\left( {{\text{OH}}} \right)_3} + 3{{\text{H}}^ + }$ and later on
${\text{Fe}}{\left( {{\text{OH}}} \right)_2} \rightleftharpoons {\text{FeO}} + {{\text{H}}_2}{\text{O}}$ .
${\text{Fe}}{\left( {{\text{OH}}} \right)_3} \rightleftharpoons {\text{FeO}}\left( {{\text{OH}}} \right) + {{\text{H}}_2}{\text{O}}$
$2{\text{FeO}}\left( {{\text{OH}}} \right) \rightleftharpoons {\text{F}}{{\text{e}}_2}{{\text{O}}_3} + {{\text{H}}_2}{\text{O}}$
The rusting of iron greatly depends on availability of oxygen and water content. Thus, rust contains hydrated iron oxides ${\text{F}}{{\text{e}}_2}{{\text{O}}_3}.{\text{n}}{{\text{H}}_2}{\text{O}}$ and iron oxide-hydroxide $\left[ {{\text{FeO}}\left( {{\text{OH}}} \right),{\text{Fe}}{{\left( {{\text{OH}}} \right)}_3}} \right]$ .

Note:
Rancidity is defined as the process of oxidation of fats and oils in a food which makes an unpleasant smell and taste. For such food, antioxidants are used to prevent damage or oxidation of food.