Table of Contents

OXIDATION AND REDUCTION

Oxidation 

(i) The addition of oxygen to a substance is called oxidation.
(ii) The removal of hydrogen from a substance is also called oxidation.

Reduction

(i) The addition of hydrogen to a substance is called reduction.
(ii) The removal of oxygen from a substance is also called reduction.

  • If a substance gains oxygen during a reaction, it is said to be oxidized.
  • If a substance loses oxygen during a reaction, it is said to be reduced.
  • If one reactant gets oxidized while the other gets reduced during a reaction.
  • Such reactions are called oxidation-reduction reactions or redox reactions.

Oxidizing agent

(i) The substance which gives oxygen for oxidation is called an oxidizing agent.
                            (ii) The substance which removes hydrogen is also called an oxidizing agent.

Reducing agent 

(i) The substance which gives hydrogen for reduction is called a reducing agent.
(ii) The substance which removes oxygen is also called a reducing agent.

EXAMPLES of Oxidation and Reduction Reaction

  • the copper(II) oxide is losing oxygen and is being reduced. The hydrogen is gaining oxygen and is being oxidized.
example of oxidation reaction of copper oxide and hydrogen to form copper and water
example of oxidation reaction of copper oxide and hydrogen to form copper and water
  • Carbon is oxidized to CO and ZnO is reduced to Zn.
oxidation reduction reaction of zinc oxide and carbon to form carbon monoxide and zinc
oxidation-reduction reaction of zinc oxide and carbon to form carbon monoxide and zinc
  • HCl is oxidized to Cl2 whereas MnO2 is reduced to MnCl2.
oxidation reduction reaction of manganese oxide and hydrochloride acid to form manganese chloride, water and chlorine gas
oxidation-reduction reaction of manganese oxide and hydrochloride acid to form manganese chloride, water and chlorine gas
example of redox reaction
example of redox reaction

 ACTIVITY 1.11

  • Heat a china dish containing about 1 g copper powder.
  • What do you observe?
  • The surface of copper powder becomes coated with black copper(II) oxide. 

  • This is because oxygen is added to copper and copper oxide is formed.
  • 2Cu + O2  →  2CuO

Important Questions on Oxidation and Reduction Reation

When copper oxide is heated with hydrogen, then copper metal and water are formed :
CuO + H2→ Cu + H2O

(i) Substance oxidized: H2
(ii) Substance reduced: CuO
(
iii) Oxidising agent: CuO
(
iv) Reducing agent: H2

 

  • In this reaction, CuO is changing into Cu.
  • That is, oxygen is being removed from copper oxide.
  • Now, by definition, removal of oxygen from a substance is called reduction, so we can say that
  • Copper oxide is being reduced to copper.
  • In this reaction, H2 is changing into H2O.
  • That is, oxygen is being added to hydrogen.
  • Now, by definition, the addition of oxygen to a substance is called oxidation, so we can say that
  • Hydrogen is being oxidized to water.
  • Copper oxide (CuO) is giving the oxygen required for the oxidation of hydrogen,
  • Therefore, copper oxide is the oxidizing agent.
  • Hydrogen is responsible for removing oxygen from copper oxide, therefore, hydrogen is the reducing agent here.

 

(i) The shiny brown coloured element X is copper metal (Cu).
(ii) When copper metal is heated in air, it forms a black coloured compound copper oxide. So, the black coloured compound is copper oxide or copper (II) oxide, CuO.

IMPORTANT QUESTIONS AND ANSWERS on Redox Reaction:

1.What is a redox reaction? When a magnesium ribbon burns in air with a dazzling flame and forms white ash, is magnesium oxidized or reduced? Why?

Ans: The reactions in which oxidation (loss of electrons) and reduction (gain of electrons) take place simultaneously are called redox reactions.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-43
Magnesium is getting oxidized because it is losing electrons to form Mg2+ and oxygen is gaining electrons to form O2-, therefore it is getting reduced.
2. You are given the following chemical equation: Mg (s) + CuO (s) MgO (s) + Cu (s)
This equation represents :
(a) decomposition reaction as well as displacement reaction
(b) combination reaction as well as double displacement reaction
(c) redox reaction as well as displacement reaction
(d) double displacement reaction as well as a redox reaction

ANS: Redox reaction as well as displacement reaction.
3. The process of respiration is :
(a) an oxidation reaction which is endothermic
(b) a reduction reaction which is exothermic
(c) a combination reaction which is endothermic
(d) an oxidation reaction which is exothermic

ANS: An oxidation reaction that is exothermic.

4. In the reaction represented by the following equation: CuO (s) + H2 (g) o Cu (s) + H2O (l)
(a) name the substance oxidized (b) name the substance reduced
(c) name the oxidizing agent (d) name the reducing agent

ANS: (a) H2

(b) CuO

(c) CuO

(d) H2

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