Question

I^- + NO₃^- ? I₂ + NO          Note: I₂ is elemental

Indicate the numeric coefficient in front of the following compounds, after balancing the reaction above

I^-

NO₃^-

I₂

NO   

Answer 1

-1    +5          0     +2

I^- + NO₃^- I₂ + NO

The oxidation reaction is : I^- I₂

The reduction reaction is : NO₃^-    NO

Balance the half recations in acidic medium.

Balancing oxidation half reaction: I^- I₂

Balance I atoms : 2I^- I₂

Balance charge( by adding electrons) : 2I^- I₂ + 2e^-                          -------------------- (1)

Balancing reduction half reaction: NO₃^-    NO

Balance O atoms(by adding H₂O ) : NO₃^-    NO+ 2 H₂O

Balance H atoms ( by adding H⁺ ions) : NO₃^- + 4H⁺   NO+ 2 H₂O

Balance charge(by adding electrons) : NO₃^- + 4H⁺ +3e^-   NO+ 2 H₂O   ----(2)

In order to get the total reaction we have to balance elecrons on both the half cells.It can be done by,

[3 x Eqn (1) ] + [ 2 x Eqn (2) ] gives

     2NO₃^- + 8H⁺ +6e^- +6I^-    2NO+ 4 H₂O + 3I₂ + 6e^-  

     2NO₃^- + 8H⁺ +6I^-   2NO+ 4 H₂O + 3I₂

This is the balanced equation.

The coefficients in front of I^-, NO₃^- , I₂ & NO are 6,2,3 & 2 respectively.