Write a balanced half-reaction for the oxidation of gaseous nitrogen dioxide to nitrate ion in acidic aqueous solution. Be sure to add physical state symbols where appropriate.

NO2(g) + H2O(l) → NO3-(aq) + 2 H+(aq) + 1 e-

Explanation:

Let’s balance the half reaction step by step (in an acidic solution):

• Balance the non-hydrogen and non-oxygen elements first

NO2(g) → NO3-(aq) (N: balanced)

• Balance oxygen by adding H2O to the side that needs oxygen (1 O : 1 H2O)

NO2(g) + H2O(l) → NO3-(aq)

• Balance hydrogen by adding H+ to the side that needs hydrogen (1 H : 1 H+)

NO2(g) + H2O(l) → NO3-(aq) + 2 H+(aq)

• Balance the charges: add electrons to the more positive side (or less negative side)

NO2(g) + H2O(l) → NO3-(aq) + 2 H+(aq)

Reactants Products

0 (-1) + (+1 x 2) = +1

+ 1 e-

0

NO2(g) + H2O(l) → NO3-(aq) + 2 H+(aq) + 1 e- → balanced half reaction

The problem mentioned that the half reaction is an oxidation reaction, and the balanced reaction is an oxidation reaction because it lost an electron