Question

2. What do you understand by rust? Represent the chemical change that occurs during rusting.




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Answer 1

Answer:

The exposure of iron (or an alloy of iron) to oxygen in the presence of moisture leads to the formation of rust.

Explanation:

. The reactants are iron (Fe), oxygen (O2) and water (H2O), and the product is iron (III) hydroxide Fe(OH)3, so Fe + O2 + H2O → Fe(OH)3.

Balanced equation is

4Fe + 3O2 + 6H2O → 4Fe(OH)3

Answer 2

Answer:

Rusting of iron refers to the formation of rust, a mixture of iron oxides, on the surface of iron objects or structures.

This rust is formed from a redox reaction between oxygen and iron in an environment containing containing high levels of moisture.

The rusting of iron is characterized by the formation of a layer of a red, flaky substance. Chemistry Behind the Rusting of Iron

The exposure of iron (or an alloy of iron) to oxygen in the presence of moisture leads to the formation of rust.

This reaction is not instantaneous.The oxygen atoms bond with iron atoms, resulting in the formation of iron oxides. This weakens the bonds between the iron atoms in the object/structure.

The reaction of the rusting of iron involves an increase in the oxidation state of iron. Rust is mostly made up of two different oxides of iron that vary in the oxidation state of the iron atom. These oxides are:

ferrous oxide. The oxidation state of iron in this compound is +2 and its chemical formula is FeO.

ferric oxide, where the iron atom exhibits an oxidation state of +3. The chemical formula of this compound is Fe2O3.

The chemical reaction is given by:

Fe → Fe2+ + 2e–

The oxidation state of iron is further increased by the oxygen atom when water is present.

4Fe2+ + O2 → 4Fe3+ + 2O2-

Now, the following acid-base reactions occur between the iron cations and the water molecules.

Fe2+ + 2H2O ⇌ Fe(OH)2 + 2H+

Fe2+ + 2H2O ⇌ Fe(OH)2 + 2H+Fe3+ + 3H2O ⇌ Fe(OH)3 + 3H+

The hydroxides of iron are also formed from the direct reaction between the iron cations and hydroxide ions.

O2 + H2O + 4e– → 4OH–

O2 + H2O + 4e– → 4OH–Fe2+ + 2OH– → Fe(OH)2

O2 + H2O + 4e– → 4OH–Fe2+ + 2OH– → Fe(OH)2Fe3+ + 3OH– → Fe(OH)3

The resulting hydroxides of iron now undergo dehydration to yield the iron oxides that constitute rust. This process involves many chemical reactions, some of which are listed below.

Fe(OH)2 ⇌ FeO + H2O

Fe(OH)2 ⇌ FeO + H2O4Fe(OH)2 + O2 + xH2O → 2Fe2O3.(x+4)H2O

Fe(OH)2 ⇌ FeO + H2O4Fe(OH)2 + O2 + xH2O → 2Fe2O3.(x+4)H2OFe(OH)3 ⇌ FeO(OH) + H2O

Fe(OH)2 ⇌ FeO + H2O4Fe(OH)2 + O2 + xH2O → 2Fe2O3.(x+4)H2OFe(OH)3 ⇌ FeO(OH) + H2OFeO(OH) ⇌ Fe2O3 + H2O

One similarity between all the chemical reactions listed above is that all of them are dependent on the presence of water and oxygen. Therefore, the rusting of iron can be controlled by limiting the amount of oxygen and water surrounding the metal.

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