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Rusting of Iron – Explanation, Chemical Reaction, Prevention

  • Last Updated : 03 Sep, 2021

A metal is a material that has a glossy appearance when freshly produced, polished, or shattered, and conducts electricity and heat reasonably well. Metals are either malleable or ductile (they may be hammered into thin sheets) (can be drawn into wires). Metals can be chemical elements like iron, alloys like stainless steel, or molecular compounds like polymeric sulphur nitride. 

The term “metal” is used more broadly in astrophysics to refer to all chemical elements in a star that are heavier than helium, rather than just classical metals. In this sense, the first four “metals” that accumulate in star cores through nucleosynthesis are carbon, nitrogen, oxygen, and neon, which are all chemically non-metals. Over the course of its existence, a star fuses lighter elements, primarily hydrogen and helium, into heavier atoms. In this context, an astronomical object’s metallicity refers to the proportion of its mass made up of heavier chemical elements.

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Rusting of Iron

Rusting is the phenomenon of a reddish-brown coating forming on the surface of iron due to the action of wet air, and the reddish-brown coating is referred to as rust. Simply said, rust is a red-brown flaky substance that forms when an iron object is exposed to wet air for an extended period of time. Rusting is the term for this phenomenon.



Rusting of iron and steel is the most prevalent example of metallic corrosion. Rusting of exhaust systems and vehicle bodywork, water pipes, and many sorts of structural steelwork are all well-known instances. The combined action of air and water on iron causes it to rust. Rusting does not happen in fully dry air or in the air that is completely devoid of water. Atmospheric conditions and the relative contributions of the components that regulate rusting define the particular composition of the rust. It is primarily composed of hydrated ferric oxide, so the chemical formula of rust is Fe2O3.xH2O .The following response can roughly characterise its formation:

4Fe + 3O2 +2xH2O → 2Fe2O3.xH2O

The outer surface of iron rusts first in the presence of wet air, and a layer of hydrated ferric oxide (rust) is deposited on the surface. This layer is delicate and porous, and if it becomes too thick, it may fall off. The lowest layers of iron are exposed to the environment, causing them to rust. Iron eventually loses its strength as the process continues.

What is the process of Rusting of Iron?

Iron rusting is an oxidation reaction. During rusting, iron combines with oxygen in the air in the presence of water to generate Fe2O3.xH2O, a hydrated iron (III) oxide.

This hydrated iron (Ill) oxide is referred to as rust. Rust is largely hydrated iron (III) oxide, Fe2O3.xH2O, as a result. The colour of rust is reddish-brown. We’ve all noticed reddish-brown rust on iron nails, screws, pipes, and railings. When exposed to wet air, not just iron, but also steel, rusts. Steel, on the other hand, is more resistant to rust than iron.

Rusting of Iron is a Chemical Change

Rust is formed when iron (or an alloy of iron) is exposed to oxygen in the presence of moisture. This reaction is not instantaneous; rather, it takes place over a long period of time. Iron oxides are formed when oxygen atoms combine with iron atoms. The bonds between the iron atoms in the object/structure are weakened as a result.

The oxidation state of iron increases as a result of the rusting reaction, which is followed by the loss of electrons. Rust is primarily composed of two types of iron oxides that differ in the oxidation state of the iron atom. These are the oxides:



  1. Iron (II) oxide is also known as ferrous oxide. This substance has an oxidation state of +2 and the chemical formula FeO.
  2. Iron(III) oxide, often known as ferric oxide, is a compound in which the iron atom has an oxidation state of +3. Fe2O3 is the chemical formula for this substance.

Iron is a reducing agent, but oxygen is an excellent oxidising agent. When exposed to oxygen, the iron atom easily gives away electrons. The chemical reaction is described as follows:

Fe → Fe2+ + 2e

When water is present, the oxygen atom increases the oxidation state of iron.

4Fe2+ + O2 → 4Fe3+ + 2O2-

The iron cations and water molecules now undergo the following acid-base reactions.

Fe2+ + 2H2O ⇌ Fe(OH)2 + 2H+

Fe3+ + 3H2O ⇌ Fe(OH)3 + 3H+

The direct reaction between the iron cations and the hydroxide ions also produces iron hydroxides.

O2 + H2O + 4e → 4OH

Fe2+ + 2OH → Fe(OH)2



Fe3+ + 3OH → Fe(OH)3

The iron hydroxides that result are now dehydrated, yielding the iron oxides that makeup rust. Many chemical processes are involved in this process, some of which are given 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\

All of the chemical reactions listed above have one thing in common: they all require the presence of water and oxygen. As a result, the amount of oxygen and water surrounding the metal can be limited to prevent rusting.

The Conditions Necessary for Rusting of Iron are:

Many factors contribute to the rusting of iron, including the amount of moisture in the air and the pH of the surrounding environment. The following are a few of these elements.

  1. Moisture: The availability of water in the environment limits the corrosion of iron. The most prevalent cause of rusting is exposure to rain.
  2. The rusting process is accelerated if the pH of the environment around the metal is low. When iron is exposed to acid rain, it rusts more quickly. Iron corrosion is slowed by a higher pH.
  3. Due to the presence of various salts in the water, iron rusts more quickly. Many ions in saltwater speed up the rusting process through electrochemical processes.
  4. Impurity: When compared to iron having a variety of metals, pure iron rusts more slowly.

The size of the iron object can also influence how quickly it rusts. A huge iron object, for example, is likely to have minor flaws due to the smelting process. These flaws provide a platform for environmental attacks on the metal.

Experiment to Prove that Air and Moisture are Essential for Rusting:

Procedure to demonstrate that rusting requires moisture and air.

  • Clean iron nails should be placed in each of the three test jars labelled A, B, and C.
  • Fill test tube A with tap water and cork it.
  • Fill test tube B with hot distilled water, then add roughly 1ml of oil and cork it. The oil will float on the surface of the water, keeping the air from evaporating.
  • Fill test tube C with anhydrous calcium chloride and cork it. Any moisture in the air will be absorbed by anhydrous calcium chloride.
  • Allow a few days for these test tubes to settle before observing.

Observation: Iron nails rust in test tube A but not in test tubes B and C, according to the results. The nails in test tube A corroded because they were exposed to both air and water. Test tube B’s nails are solely exposed to water, but test tube C’s nails are exposed to dry air.

Conclusion: This experiment demonstrates that rusting requires both air (oxygen) and moisture to occur.



What are the damages caused by Rusting of Iron objects?

Rust is permeable and soft, and as it slips off the surface of a rusty iron object, the iron beneath rusts. As a result, iron rust is a constant process that eats away at iron items over time, rendering them worthless. Rusting of iron causes significant damage over time since it is used to build a wide range of structures and commodities, including bridges, grills, railings, gates, and the bodies of cars, buses, trucks, and ships. It goes without saying that we should have a way to keep iron from rusting.

Prevention of Rusting of Iron

The loss of iron objects due to rusting has a huge economic impact on the country, and it must be avoided. To keep iron things from rusting, a variety of techniques are employed. To keep air and water out, the majority of the ways require covering the iron piece with something. The following are some of the most prevalent ways to keep iron from rusting:

  1. Rusting of iron can be prevented by painting: Coating the surface of the iron with paint is the most popular way to keep it from rusting. When the paint is placed on the surface of an iron object, it prevents air and moisture from getting into touch with the object, preventing rusting. To prevent rusting, window grills, railings, iron bridges, steel furnishings, railway coaches, and the bodies of automobiles, buses, and trucks, among other things, are all painted on a regular basis.
  2. Rusting of iron can be prevented by applying grease or oil: When grease or oil is placed on the surface of an iron object, air and moisture are kept from coming into touch with it, preventing corrosion. Iron and steel tools and machine parts, for example, are rubbed with grease or oil to prevent corrosion.
  3. Rusting of iron can be prevented by galvanisation: Galvanizing protects articles exposed to excessive moisture, such as roof sheets and pipelines, against rusting. Galvanization is the technique of applying a thin layer of zinc to steel and iron to prevent rust. Galvanised iron is iron that has been zinc-coated. Zinc is more reactive than iron, therefore in the presence of moisture, it interacts with oxygen to generate an invisible layer of zinc oxide that protects it from further rusting. It’s worth noting that even if the zinc coating on galvanised iron products is broken, they remain rust-free. Because zinc is more reactive than iron, this is the case.
  4. Rusting of iron can be prevented by electroplating: Electroplating is another method for keeping items from rusting. In this procedure, noncorroding metals including tin, nickel, and chromium are electroplated on iron. This technique not only keeps the goods from rusting but also improves their beauty. Bathroom fittings and vehicle elements such as bicycle handlebars, car bumpers, and so on are examples of chromium-plated items.
  5. Rusting of iron can be prevented by alloying it to make stainless steel: Stainless steel is created when the iron is alloyed with chromium and nickel. Stainless steel is impervious to rust. Stainless steel cooking utensils, scissors, and medical equipment, for example, do not corrode. Stainless steel, on the other hand, is too expensive to be utilised in big quantities.
  6. Rusting of iron can be prevented by tinning: Tin is non-toxic, and its reactivity is lower than that of iron. Food cans are tinned, which implies that they have a thin layer of tin on them. As a result, when an electroplated thin coating of tin metal is deposited on iron and steel items, the iron and steel objects are protected from rusting. Tin-plated tiffin boxes are utilised because they are non-toxic and do not contaminate the food within.
  7. Rusting of iron can be prevented by Enameling: Enamelling is a high-heat procedure that involves fusing powdered glass into a metal substrate. Enamels can be used on a variety of surfaces, including glass and ceramics.

Sample Problems

Question 1: What is the process of rusting iron?

Answer:

Iron rusting is an oxidation reaction. In the presence of water, the iron metal interacts with oxygen in the air to generate hydrated iron (III) oxide, Fe2O3.xH2O. This hydrated iron (III) oxide is referred to as rust. Rust is largely hydrated iron (III) oxide, Fe2O3.xH2O, as a result. Rust is a reddish-brown hue

Question 2: What is rusting of iron called?

Answer:

Rusting is the phenomena of a reddish-brown coating forming on the surface of iron due to the action of wet air, and the reddish-brown coating is referred to as rust.

Question 3:  How rusting of iron can be prevented?



Answer:

Rusting of iron can be prevented by

  • Applying paint
  • Applying grease or oil
  • By galvanisation
  • By electroplating
  • Using alloying iron to make stainless steel
  • By tinning
  • Using Enameling

Question 4: What is rust? Give the equation for the formation of rust?

Answer:

When iron is exposed to air for an extended period of time, it oxidises and develops a reddish-brown iron oxide on the surface. Rust is the name for this reddish-brown material.

Rust is formed via the following equation:

4Fe + 3O2 +2xH2O → 2Fe2O3.xH2O

Question 5: How does rust damage iron objects?

Answer:

Rust is permeable and soft, and as it slips off the surface of a rusty iron object, the iron beneath rusts. As a result, iron rust is a constant process that eats away at iron items over time, rendering them worthless. Rusting of iron causes significant damage over time since it is used to build a wide range of structures and commodities, including bridges, grills, railings, gates, and the bodies of cars, buses, trucks, and ships. It goes without saying that we should have a way to keep iron from rusting.

Question 6: What are the conditions necessary for rusting?

Answer:

Many factors contribute to the rusting of iron, including the amount of moisture in the air and the pH of the surrounding environment. The following are a few of these elements.

  • Moisture: The availability of water in the environment limits the corrosion of iron. The most prevalent cause of rusting is exposure to rain.
  • The rusting process is accelerated if the pH of the environment around the metal is low. When iron is exposed to acid rain, it rusts more quickly. Iron corrosion is slowed by a higher pH.
  • Due to the presence of various salts in the water, iron rusts more quickly. Many ions in saltwater speed up the rusting process through electrochemical processes.
  • Impurity: When compared to iron having a variety of metals, pure iron rusts more slowly.

Question 7: How does rust of iron be a chemical change?

Answer:

Rust is made up of iron oxide (Fe2O3). As a result, rust and iron are not synonymous. Rust isn’t the same thing as the iron it’s deposited on. Because a new component termed “iron oxide” is created during the rusting of iron, it represents a chemical change.




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