Chemistry Class 11 NCERT Solutions: Chapter 8 Redox Reactions Part 10

Q: 19. Balance the following equations in basic medium by ion-electron method and oxidation number methods and identify the oxidising agent and the reducing agent.

(A) Equation

(B) Equation

(C) Equation

Answer:

(A) The O.N. (Oxidation Number) of P decreases from 0 in Equation to Equation in Equation and increases from 0 in Equation . Hence, Equation acts both as an oxidizing agent and a reducing agent in this reaction.

Ion-electron method

The oxidation half equation is:

Equation

The P atom is balanced as:

Equation

The O.N. is balanced by adding 8 electrons as:

Equation

The charge is balanced by adding Equation as

Equation

The H and O atoms are balanced by adding Equation as:

Equation

The reduction half equation is:

Equation

The P atom is balanced as

Equation

The O.N. is balanced by adding 12 electrons as:

Equation

The charge is balanced by adding Equation as:

Equation (ii)

By multiplying equation (i) with 3 and (ii) with 2 then adding them, the balanced chemical equation can be obtained as:

Equation

(B)

Q 19 B­ Structure of O.N. of N and Cl increases & decreses per atom

Q 19 B Structure of O.N. Of N and Cl Increases & Decreses Per Atom

Q 19 B­ Structure of O.N. of N and Cl increases & decreses per atom

The oxidation number of N increases from Equation and the oxidation number of Cl decreases from Equation . Hence, in this reaction, Equation is the reducing agent and Equation is the oxidizing agent.

Ion – electron method:

The oxidation half equation is:

Equation

The N atoms are balance as:

Equation

The oxidation number is balanced by adding 8 electrons as:

Equation

The charge is balanced by adding 8 Equation

Equation

The O atoms balanced by adding Equation as:

Equation

The reduction half equation is:

Equation

The oxidation number is balanced by adding 6 electrons as:

Equation

The charge is balanced by adding Equation ions as:

Equation

The O atoms are balanced by adding Equation as:

Equation

Equation The balanced equation can be obtained by multiplying equation (i) with 3 and equation (ii) with 4 and then adding them as:

Equation

Oxidation number method:

Total decrease in oxidation number of N Equation

Total Increase in oxidation number of Cl Equation

On multiplying Equation with 3 and Equation with 4 to balance the increase and decrease in O.N., we get:

Equation

The N and Cl atoms are balanced as:

Equation

The O atoms are balanced by adding Equation as:

Equation

This is the required balanced equation.

(C)

Q 19 C­ Structure of O.N. of N and Cl increases & decreses per atom

Q 19 C­ Structure of O.N. Of N and Cl Increases & Decreses Per Atom

Q 19 C­ Structure of O.N. of N and Cl increases & decreses per atom

The oxidation number of Cl decreases from + 7 in Equation and the oxidation number of O increases from Equation to zero in Equation . Hence, in this reaction, Equation is the oxidizing agent and Equation is the reducing agent.

Ion- electron method:

The oxidation half equation is:

Equation

The charge is balanced by adding Equation

Equation …(i)

The reduction half equation is:

Equation

The Cl atoms are balanced as:

Equation

The oxidation number is balanced by adding 8 electrons as:

Equation

The charge is balanced by adding Equation as

Equation

The oxygen atoms are balanced by adding Equation as:

Equation ……(ii)

The balanced equation can be obtained by multiplying equation (i) with 4 and adding equation (ii) to it as:

Equation

Oxidation number method:

Total decrease in oxidation number of Equation Equation

Total Increase in oxidation number of Equation Equation

By multiplying Equation and Equation with 4 to balance the increase and decrease in the oxidation number, we get:

Equation

The Cl atoms are balanced as:

Equation

The O atoms are balanced by adding Equation as:

Equation

The H atoms are balanced by adding Equation and Equation as:

Equation

This is the required balanced equation.

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