[ajax0604]

From this equation 2Cu(NO₃)₂  2CuO + 4NO₂ + O₂, I have identified that the same substance undergoes oxidation and reduction. The question wants the reductant and oxidant identified. Should I write Cu(NO₃)₂ or just NO₃^-, since it is the nitrate ion that is actually reacting. Would both be acceptable?

On a related problem, for this equation HNO₂ + H₂O₂  HNO₃ + H₂O, does it matter whether you write the reduction half equation as NO₂^- + H₂O  NO₃^- +2H⁺ +2e^- or HNO₂ + H₂O  HNO₃ +2H⁺ +2e^- ?

[Hunter2]

For the first question its enough to write the Ions, which undergo a reduction or oxidation. So NO₃^- is enough.

The second question: both is possible. Its not a mistake to write the acid or the Anion. Hydrogen ions any way present.

[Borek]

Nitrous acid is a weak one, so as long as we are talking about acid reacting I would prefer the HNO₂ form. NO₂^- would be OK with me in any solution with pH above 4 (that automatically includes all solutions of salts of the nitrous acid).