Table of Contents

EFFECTS OF OXIDATION REACTIONS IN EVERYDAY LIFE

  • Oxidation has a damaging effect on metals as well as on food.
  • There are two common effects of oxidation reactions that we observe in daily life.
    • Corrosion of metals
    • Rancidity of food.

CORROSION

  • When a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion.

  • Rusting of iron metal is the most common form of corrosion
  • Iron articles are shiny when new, but get coated with a reddish-brown powder when left for some time. 
  • Iron metal is oxidized by the oxygen of air in the presence of water (moisture) to form hydrated iron (III) oxide called rust :
    4Fe + 3O2 + 2xH2O     →2Fe2O3.xH2O
  • The black coating on silver and the green coating on copper are some examples of corrosion.
  • Corrosion causes damage to car bodies, bridges, iron railings, ships, and to all objects made of metals, especially those of iron.
  • Coating metal surface with paint or enamel provides a barrier between the metal and the moisture in the environment.
  • The process of coating a metal surface with another metal that is more likely to be oxidized is referred to as sacrificial coating.
surface coating to prevent corrosion
surface coating to prevent corrosion

IMPORTANT QUESTIONS AND ANSWERS On Corrosion

1. (a) Explain the term “corrosion” with an example. Write a chemical equation to show the process of corrosion of iron.
(b) What special name is given to the corrosion of iron?
(c) What type of chemical reaction is involved in the corrosion of iron?   

ANS:

a)corrosion; When a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion. 
b)corrosion of iron is rusting process
c)  4Fe + 3O2 + 2xH2O →2Fe2O3.xH2

RANCIDITY

  • When fats and oils are oxidized, they become rancid, and their smell and taste change.
  • There are many ways to prevent rancidity

  • substances that prevent oxidation (antioxidants) are added to foods containing fats and oil.
  • Keeping food in airtight containers helps to slow down oxidation.

 

IMPORTANT QUESTIONS AND ANSWERS On Rancidity

1.What are anti-oxidants? Why are they added to fat and oil-containing foods?

ANS: substances that prevent oxidation is called antioxidants are added to foods containing fats and oil. They prevent oil from rancidity. 

2.Name two anti-oxidants that are usually added to fat and oil-containing foods to prevent rancidity.

ANS: Ascorbic acid, gallic acid.

  • Rancidity can be prevented by adding anti-oxidants to foods containing fats and oils
    • Anti-oxidants are actually reducing agents.
    • When antioxidants are added to foods, then the fats and oils present in them do not get oxidized easily and hence do not turn rancid.
    • So the foods remain good to eat for a much longer time.
    • The two common anti-oxidants used in foods to prevent the development of rancidity are BHA (Butylated Hydroxy-Anisole) and BHT (Butylated Hydroxy-Toluene).
  • Rancidity can be prevented by packaging fat and oil-containing foods in nitrogen gas.
    • When the packed food is surrounded by unreactive gas nitrogen, there is no oxygen (of air) to cause its oxidation
      and make it rancid.
    • The manufacturers of potato chips (and other similar food products) fill the plastic bags containing chips with nitrogen gas to prevent the chips from being oxidized and turn rancid.
  • Rancidity can be retarded by keeping food in a refrigerator
    • The refrigerator has a low temperature inside it.
    • When the food is kept in a refrigerator, the oxidation of fats and oils in it is slowed down due to low temperature.
    • So, the development of rancidity due to oxidation is retarded.
  • Rancidity can be retarded by storing food in air-tight containers.
    • When food is stored in air-tight containers, then there is little exposure to the oxygen of the air.
    • Due to reduced exposure to oxygen, the oxidation of fats and oils present in food is slowed down and hence the development of rancidity is retarded.
  • Rancidity can be retarded by storing foods away from light.
    • In the absence of light, the oxidation of fats and oils present in food is slowed down and hence the development of rancidity is retarded.
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