Effect of Redox Reactions: Corrosion & Rancidity

Rancidity is important in view of its direct link with foods and edibles. Both, corrosion and rancidity, are results of redox reactions.

Corrosion

Corrosion is a destructive chemical process in which metals are oxidized in presence of air and moisture. The rusting of iron, tarnishing of silver, development of green coatings on copper, brass and bronze are a few examples of corrosion.

It causes enormous damage to bridges, ships, cars and to all machines which are made of iron or steel. The damage and efforts taken to prevent it costs several crores of rupees a year. Preventing corrosion is a big challenge for an industrially developing country.

How to prevent corrosion?

There are several methods for protecting metals from corrosion, especially iron from rusting:

  • Plating the metal (iron) with a thin layer of less easily oxidized metal like nickel or chromium. This plating keeps out air (oxygen) and moisture which are main causes of corrosion.

  • Coating or connecting the metal with more reactive metal or with a metal which is more easily oxidized. For example, iron is connected to magnesium or coated with zinc for protecting it from corrosion. Iron rods are dipped in molten zinc to create a layer on their surface. This process of zinc coating over iron is called galvanization.

  • Applying a protective coating such as paint.

Rancidity

Fats and oils undergo oxidation and become rancid. This change is called rancidity. Oxidation of fats or oils results into the formation of acids. These acids give unpleasant smell and bad taste.

Many food items which are cooked or fried in oil or fat are kept in air tight containers for sale. Keeping food items in air tight containers helps to slow down the oxidation process. Usually substances which prevent oxidation (anti-oxidants) are added to food items containing fats and oils.