Question

3. Why does iron rust? How can it be prevented? Describe two methods to prevent rusting.​

Answer 1

Answer:

iron rust when it comes in contact with the moisture in the atmosphere. it can be prevented by applying oil or painting it with paint.

Explanation:

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Answer 2

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 water (such as air containing high levels of moisture). The rusting of iron is characterized by the formation of a layer of a red, flaky substance that easily crumbles into a powder.

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, it generally proceeds over a considerably large time frame. 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, accompanied by a loss of electrons. Rust is mostly made up of two different oxides of iron that vary in the oxidation state of the iron atom. These oxides are:

Iron(II) oxide or ferrous oxide. The oxidation state of iron in this compound is +2 and its chemical formula is FeO.

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

Oxygen is a very good oxidizing agent whereas iron is a reducing agent. Therefore, the iron atom readily gives up electrons when exposed to oxygen. 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+

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–

Fe2+ + 2OH– → Fe(OH)2

Fe3+ + 3OH– → Fe(OH)3

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

Fe(OH)2 ⇌ FeO + H2O

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

Fe(OH)3 ⇌ FeO(OH) + H2O

FeO(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.

Galvanization

Galvanization is the process of applying a protective layer of zinc on a metal. It is a very common method of preventing the rusting of iron.

This can be done by dipping the metal to be protected in hot, molten zinc or by the process of electroplating.

Zinc is a relatively cheap metal that sticks to steel easily. It also offers cathodic protection to the iron surface by acting as an anode. The zinc layer is corroded instead of the iron due to this.

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