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Corrosion and rusting

Tutormate > CBSE Syllabus-Class 10th Chemistry > Corrosion and rusting

03 Metals and non-metals


  • The eating up of metals by the action of air, moisture or a chemical (such as an acid) on their surface is called corrosion.
  • So, reactive metals such as potassium and sodium are kept in kerosene oil to avoid their exposure to the atmosphere.


  • The corrosion of metals increases in presence of oxygen.
  • Metals placed higher in the reactivity series corrode more easily.
  • The rate of corrosion is enhanced even by the dissolved salts in water which act as an electrolyte. For example, iron corrodes faster in seawater.


  • Barrier protection:
    • It is done by a coating of one metal with another metal with the help of electricity (electroplating).
    • So, the metal surface is not allowed to come in contact with the atmospheric agents like air and water and hence it is protected from corrosion.
  • Sacrificial protection:
    • Electropositive metal such as zinc or magnesium, are used to cover the metal to be protected.
    • These metals, being more electropositive get oxidized and save the metal from corrosion.
  • Cathode protection:
    • The metal object that is to be protected from rusting is connected to a piece of more electropositive metal like zinc.
    • The anode is made up of a more reactive element which loses electrons and gets oxidized and thus saves the cathode form rusting.


  • Rust is mainly hydrated iron (oxide, Fe2O3xH2O.
  • The corrosion of iron is called as rusting. A reddish coating is developed on the surface of articles made up of iron, when it is exposed to the atmosphere.
  • Rust is a red-brown coloured substance.
  • It is not only the iron which rusts, even the steel rusts on exposure to damp air (or if exposed to water). But steel rusts less readily than iron.
  • Rust is an oxide of the metal formed by the reaction with the oxygen present in the atmosphere.


  • Presence of air (or oxygen)
  • Presence of water (or moisture)
  • The presence of pollutants, for example, NO2 and CO2 also enhances rusting.


  • Painting. Coat the surface of the iron with paint. This restricts the contact of air and moisture on the iron object.
  • By applying grease or oil. This restricts the contact of air and moisture on the iron surface.
  • Galvanisation:
    • The process of depositing a thin layer of zinc metal on iron objects is called galvanisation.
    • This can be done by dipping an iron object in molten zinc metal.
    • This results to the formation of a thin layer of zinc metal over the iron object.
    • This layer of zinc metal in turn protects iron objects from exposure to damp air.
  • Tin-plating and chromium-plating.
    • Tin and chromium metals are resistant to corrosion. So, the electroplating prevents from rusting of projects.
    • For example, tiffin-boxes made of steel are nickel-plated in and out to protect them from rusting.
    • As tin is non-poisonous, it is used for plating tiffin-boxes, hence does not contaminate the food kept in them.
    • Chromium –plating is done on taps, bicycle handle bars and car bumpers made of iron.
  • By Alloying
    • Stainless steel is obtained, when iron is alloyed with chromium and nickel. Stainless steel does not rust at all.
    • Cooking utensils, Knives, scissors and surgical instruments, etc., are made of stainless steel.


  • Aluminium vessels lose their shine and become dull very soon after use.
  • This occurs due to the corrosion of aluminium metal when exposed to moist air.
  • The process of thickening layer of aluminium oxide on the surface of aluminium objects by electrolysis known as anodizing.
  • This process adds on the protection from corrosion.


  • In damp air copper reacts slowly with the carbon dioxide and water of air to form a green coating of copper carbonate on the surface of the object.
  • This corrodes the copper. Cleaning of the corroded copper vessels with dilute acid solution dissolves green coloured copper carbonate present on the corroded copper vessels.
  • This makes them look shiny, red-brown again.

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