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Corrosion
Master Corrosion: Understand how metals degrade and food spoils due to oxidation reactions in everyday life. Learn the core definitions, everyday chemical examples, and prevention methods through clear explanations and board-style practice questions.
1.0Learning Outcomes
After completing this lesson, you will be able to:
- Define corrosion and rancidity in the context of oxidation.
- Identify chemical formulas and specific color changes caused by corrosion in different metals.
- Explain why food containing fats and oils spoils and list practical methods to prevent it.
- Analyze chemical equations linked to daily life oxidation effects.
- Solve NCERT and board-level questions confidently.
Introduction
The chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties is called corrosion.
The corrosion causes damage to buildings, ships and many other articles especially made of iron. During corrosion, metal gets changed into its oxide, sulphide, carbonate etc.
The most common example of corrosion is rusting of iron.
2.0Rust
Iron corrodes readily when exposed to moisture and gets covered with a brown flaky substance called rust. It is called rusting of iron.
Rust is hydrated Iron (III) oxide [Fe2O3.2H2O]
3.0Some more examples of corrosion
(i) Copper reacts with moist carbon dioxide in the air and slowly loses its shiny brown surface and acquires a green coating of basic copper carbonate.
(ii) Silver articles become black after sometime when exposed to air.
4.0Rancidity
The oxidation of oils or fats in food, resulting in a bad taste and bad smell is called rancidity. It is caused due to prolonged exposure of food in the air. Oxygen present in air oxidizes fats / oils present in food and forms volatile substances, which have bad odour.
Prevention of Rancidity
(i) Rancidity can be prevented by adding antioxidants to foods containing fats and oils. Antioxidants are reducing agents which when added to food, the food do not get oxidised easily and hence do not turn rancid easily.
Common Antioxidants
(a) BHA (Butylated Hydroxy Anisole)
(b) BHT (Butylated Hydroxy Toluene)
(i) Vitamin-E (tocopherol) and vitamin-C (ascorbic acid) are the two naturally occuring antioxidants.
(ii) Rancidity can be prevented by packaging fat and oil containing foods in the presence of nitrogen gas.
(iii) It can be retarded by keeping food in the refrigerator.
(iv) It can also be retarded by storing food in airtight containers.
(v) It can be retarded by storing foods away from light.
5.0Crystallization
Crystallization is the solidification of atoms or molecules into a highly structured form called a crystal. Usually, this refers to the slow precipitation of crystals from a solution of a substance.
The process of obtaining crystals of pure substances from their saturated solution is called crystallisation. Substances like sugar, salt, urea and copper sulphate can be obtained by crystallisation.
Crystallisation is an example of physical change because it is reversible and involves only changes in shape and size. For example, copper sulphate is a blue-coloured crystal that is obtained by heating the aqueous solution of copper sulphate.
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7.0Supporting Study Materials
This study material CBSE Notes and NCERT Solutions for the Chapter "Metals and Non-Metals" on Corrosion Topics is designed according to the latest CBSE Class 10 Science syllabus and NCERT guidelines. It provides clear explanations of key concepts, definitions, examples, and important questions to help students understand redox reactions, corrosion, and rancidity, and prepare effectively for examinations.
8.0Previous Year Questions (PYQs)
Q1. Why do we apply paint on iron articles? (CBSE Board)
Answer: Paint forms a protective barrier over the surface of iron articles. This prevents the iron metal from coming into direct contact with moisture (water) and oxygen present in the atmosphere, thereby stopping the chemical process of rusting.
Q2. Oil and fat-containing food items are flushed with nitrogen. Why? (CBSE Board)
Answer: Nitrogen is an inert (highly unreactive) gas. When fat-containing food items are packed with nitrogen, it replaces oxygen from the container. In the absence of oxygen, the oils and fats inside the food cannot undergo oxidation, which effectively prevents the food from turning rancid, preserving its smell and taste.
9.030-Second Revision
- Corrosion is the gradual deterioration of metals due to reactions with air and moisture.
- Rusting is the corrosion of iron.
- Rust is hydrated iron(III) oxide (Fe₂O₃·xH₂O).
- Air and water are essential for rusting.
- Corrosion weakens metals and damages structures.
- Iron gates, bridges, and vehicles are prone to rusting.
- Painting prevents contact with air and moisture.
- Galvanisation protects iron by coating it with zinc.
- Oiling and greasing help prevent corrosion.
- Remember: Air + Moisture + Metal = Corrosion
10.0Recommended Next Topics
- Oxidation and Reduction (Redox Reactions)
- Reactivity Series of Metals
- Types of Chemical Reactions
- Acids, Bases and Salts