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Balance the Following Equations in Basic Medium by Ion-electron Method and Oxidation Number Methods and Identify the Oxidising Agent and the Reducing Agent. - CBSE (Science) Class 11 - Chemistry

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Question

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

`Cl_2O_(7(g)) + H_2O_(2(aq)) -> ClO_(2(aq))^- + O_(2(g)) + H_(aq)^+`

Solution

The oxidation number of Cl decreases from + 7 in Cl2O7 to + 3 in `ClO_2^-` and the oxidation number of O increases from – 1 in H2O2 to zero in O2. Hence, in this reaction, Cl2O7 is the oxidizing agent and H2O2 is the reducing agent.

Ion–electron method:

The oxidation half equation is:

The oxidation number is balanced by adding 2 electrons as:

`H_2O_(2(aq)) -> O_(2(g)) + 2e^(-)`

The charge is balanced by adding 2OHions as:

`H_2O_2(aq) -> + 2OH_((aq))^(-) -> O_(2(g)) + 2e^(-)`

The oxygen atoms are balanced by adding 2H2O as:

`H_2O_(2(aq)) + 2OH_(aq)^(-) -> O_(2(g)) + 2H_2O_(i) + 2e^(-)`  ....(i)

The reduction half equation is:

The Cl atoms are balanced as:

`Cl_2O_(7(g)) + 8e^(-) -> 2ClO_(2(aq))^- + 6OH_((aq))^-`

The oxygen atoms are balanced by adding 3H2O as:

`Cl_2O_(7(g)) + 3H_2O_((l)) 8e^(-) ->  2ClO_(2(aq))^- + 6OH_(aq)^-`   (ii)

The balanced equation can be obtained by multiplying equation (i) with 4 and adding equation (ii) to it as: `Cl_2O_(7(g)) + 4H_2O_(2(aq)) + 2OH_(aq))^(-)  -> 2ClI_(2(aq))^(-) + 4O_(2(g)) + 5H_2O_(l)`

Oxidation number method:

Total decrease in oxidation number of Cl2O= 4 × 2 = 8

Total increase in oxidation number of H2O2 = 2 × 1 = 2

By multiplying H2O2 and O2 with 4 to balance the increase and decrease in the oxidation number, we get:

`Cl_2O_(7(g)) + 4H_2O_(2(aq)) -> ClO_(2(aq))^(-) + 4O_(2(g))`

The Cl atoms are balanced as:

`Cl_2O_(7(g)) + 4H_2O_(2(aq)) -> 2ClO_(2(aq))^-

 + 4O_(2(g))`

The O atoms are balanced by adding 3H2O as:

`Cl_2O_(7(g)) + 4H_2O_(2(aq)) -> 2ClO_(2(aq))^- + 4O_(2(g)) + 3H_2O_(l)`

The H atoms are balanced by adding 2OH and 2H2O as:

`Cl_2O_(7(g)) + 4H_2O_(2(aq)) + 2OH_((aq))^(-) -> 2ClO_(2(aq))^- + 4O_(2(g)) + 5H_2O_(l)`

This is the required balanced equation.

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APPEARS IN

 NCERT Solution for Chemistry Textbook for Class 11 (2018 to Current)
Chapter 8: Redox Reactions
Q: 19.3 | Page no. 274
Solution Balance the Following Equations in Basic Medium by Ion-electron Method and Oxidation Number Methods and Identify the Oxidising Agent and the Reducing Agent. Concept: Oxidation Number - Balancing of Redox Reactions.
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