Question

The following skeletal oxidation-reduction reaction occurs under acidic conditions. Write the balanced REDUCTION half reaction.

Cl₂+ NO₃^- ClO₃^-+ HNO₂

Answer 1

Reduction half reaction is

NO3- $\to$ HNO2  

Oxidation state of N in  NO3- = +5 ; Oxidation state of N in  HNO2  = +3

so, N atom is reduced .

To balance oxygen atom 1 water molecule is added to right side

NO3-  $\to$ HNO2  + H2O

as the medium is acidic, to balance H atom 3 H+ is added to left side

NO3-  + 3H+  $\to$ HNO2  + H2O

total charge on left side = ( -1 +3) = + 2 , toatl charge on right side = 0

to balance the charge 2e- is added to left side

NO3-  + 3H+ +2e-   $\to$ HNO2  + H2O

Therefore the final balanced reduction half reaction is

NO3-  + 3H+ + 2e- $\to$ HNO2  + H2O