Class 10 Chemistry Notes: Oxidation and reduction l Redox Reactions

Table of Contents

• Oxidation and Reduction
• Activity 1.11: Observing Oxidation and Reduction
• Redox Reactions
• Examples of Redox Reactions
• Effects of Oxidation Reactions in Everyday Life
• Corrosion
• Rancidity
• FAQs

Oxidation and Reduction

Oxidation and reduction are two fundamental chemical processes that involve the transfer of oxygen or hydrogen between reactants. Understanding these processes is essential in the study of chemistry as they form the basis for many reactions and applications in daily life and industry.

Activity 1.11: Observing Oxidation and Reduction

To observe a simple oxidation reaction, perform the following activity:

• Heat a china dish containing about 1 g of copper powder.
• Observe the surface of the copper powder.

Observation: The surface of the copper powder becomes coated with black copper(II) oxide. This black substance forms because oxygen is added to copper, resulting in copper oxide.

$2Cu + O_2 \xrightarrow{\text{Heat}} 2CuO$

If hydrogen gas is passed over this heated copper oxide, the black coating on the surface turns brown as copper is obtained through a reduction reaction.

$CuO + H_2 \xrightarrow{\text{Heat}} Cu + H_2O$

Redox Reactions

In a redox reaction, one reactant gets oxidized (loses electrons) while the other gets reduced (gains electrons). For instance, in the reaction between copper(II) oxide and hydrogen:

• Copper(II) oxide loses oxygen and is reduced to copper.
• Hydrogen gains oxygen and is oxidized to water.

Such reactions are termed oxidation-reduction or redox reactions.

Examples of Redox Reactions

Consider the following examples of redox reactions:

Reaction Between Zinc Oxide and Carbon:

$ZnO + C \rightarrow Zn + CO$

• Carbon is oxidized to carbon monoxide.
• Zinc oxide is reduced to zinc.

Reaction Between Manganese Dioxide and Hydrochloric Acid:

$MnO_2 + 4HCl \rightarrow MnCl_2 + 2H_2O + Cl_2$

• Hydrochloric acid is oxidized to chlorine gas.
• Manganese dioxide is reduced to manganese chloride.

Effects of Oxidation Reactions in Everyday Life

Corrosion

Corrosion is a process where metals are gradually destroyed by chemical reactions with environmental elements. For example, iron forms a reddish-brown layer of rust when exposed to moisture and air. Similarly, silver tarnishes and copper forms a green patina due to corrosion. Corrosion can cause significant damage to structures and objects made of metal.

Rancidity

Rancidity occurs when fats and oils in food become oxidized, leading to a change in taste and smell. To prevent rancidity, antioxidants are added to food, and airtight containers are used to limit exposure to oxygen. For instance, chip manufacturers often flush bags with nitrogen to prevent oxidation.

FAQs

Q: What is oxidation?
A: Oxidation is the process where a substance gains oxygen or loses hydrogen during a chemical reaction.

Q: What is reduction?
A: Reduction is the process where a substance loses oxygen or gains hydrogen during a chemical reaction.

Q: Can you give an example of a redox reaction?
A: Yes, the reaction between copper(II) oxide and hydrogen is a redox reaction where copper(II) oxide is reduced to copper and hydrogen is oxidized to water.

Q: What is corrosion?
A: Corrosion is the gradual destruction of metals due to chemical reactions with environmental elements such as moisture and acids.

Q: How can rancidity be prevented?
A: Rancidity can be prevented by adding antioxidants to food, storing food in airtight containers, and using gases like nitrogen to prevent oxidation.

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