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.
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.
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?
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.xH2O
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.