# 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)

(B)

(C)

Answer:

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

Ion-electron method

The oxidation half equation is:

The P atom is balanced as:

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

The charge is balanced by adding as

The H and O atoms are balanced by adding as:

The reduction half equation is:

The P atom is balanced as

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

The charge is balanced by adding as:

(ii)

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

(B)

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

Ion – electron method:

The oxidation half equation is:

The N atoms are balance as:

The oxidation number is balanced by adding 8 electrons as:

The charge is balanced by adding 8

The O atoms balanced by adding as:

The reduction half equation is:

The oxidation number is balanced by adding 6 electrons as:

The charge is balanced by adding ions as:

The O atoms are balanced by adding as:

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

Oxidation number method:

Total decrease in oxidation number of N

Total Increase in oxidation number of Cl

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

The N and Cl atoms are balanced as:

The O atoms are balanced by adding as:

This is the required balanced equation.

(C)

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

Ion- electron method:

The oxidation half equation is:

The charge is balanced by adding

…(i)

The reduction half equation is:

The Cl atoms are balanced as:

The oxidation number is balanced by adding 8 electrons as:

The charge is balanced by adding as

The oxygen atoms are balanced by adding as:

……(ii)

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

Oxidation number method:

Total decrease in oxidation number of

Total Increase in oxidation number of

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

The Cl atoms are balanced as:

The O atoms are balanced by adding as:

The H atoms are balanced by adding and as:

This is the required balanced equation.