Please balance the following chemical equation by oxidation number method (redox reaction).

Asked by Balbir | 26th Jan, 2018, 09:06: PM

Expert Answer:

In most situations of balancing an equation, you are not told whether the reaction is redox or not.

In these circumstances, you can use a procedure called the oxidation number method.

Step 1

The skeleton equation is:

I2  +  HNO3  →  HIO3  +  NO2  +  H2O

Step 2

The oxidation number of various atoms involved in the reaction.

 0     +1 +5 -2     +1 +5 -2    +4  -2     +1  -2         

I2  +  HNO3  →  HIO3  +  NO2  +  H2O

Step 3

For N oxidation number changes from +5 to +4 so it is reduced. For I oxidation number changes from 0 to +5 so it is oxidized. No change in oxidation number of O.

Step 4

Determine the net increase in oxidation number for the element that is oxidized and the net decrease in oxidation number for the element that is reduced.

For I  0 to +5                                   Net change = +5   ......... Oxidation

For N +5 to +4                                 Net change = -1    ..........Reduction

Step 5

Determine a ratio of oxidized to reduced atoms that would yield a net increase in oxidation number equal to the net decrease in oxidation number.

I atoms would yield a net increase in oxidation number of +5. (five electrons would be lost by five atoms.). 1 N atom would yield a net decrease of -1. (One N atom would gain three electrons.)

Thus the ratio of I atoms to N atoms is 5:1.But we have I2 as a reactant then the ratio becomes 10:1

Step 6

To get the ratio identified in Step 5, add coefficients to the formulas which contain the elements whose oxidation number is changing.

and we will get the balanced equation,

I2  + 10 HNO3  →  2HIO3  +  10NO2  +  4H2O

 

Answered by Ramandeep | 29th Jan, 2018, 11:50: AM