[maakii]

Hello everyone!

I have a solution of acidic copper (II) nitrate, which I am electrolysing. I know that Cu2+ will be reduced into Cu at the cathode, however, can anyone explain why this reaction is favoured over the reduction of NO3 into NO2 and H2O?

NO3−(aq) + 2 H+ +  e−    NO2(g) +  H2O    E= +0.80 V
Cu2+ + 2 e−  Cu(s)     E=+0.340V

Is this merely because the activation energy for the reduction of nitrates is higher (i.e. kinetics)? If so, under what conditions will reduction of NO3 occur?

Secondly,

I also have some ammonium nitrate in my solution, which I have read will produce tetraanime copper (II) nitrate (an explosive)?! Will it still be produced even in low concentrations of ammonium? Thank you!

[Nobby]

I don't think this reaction will takes place. Because Reduction can only take place at the Cathode, but on the Anode oxidizing takes place. Nitrate is already in highest oxidation number. So Oxygen will be developed.

On the cathode Nitrate will reduced if no Metal (Cu) is present.

2 H₂O => O₂ + 4 H⁺ + 4 e^-

Tetraamminecopper will not developed, because we have Ammonium not Ammonia in the solution.

[DevaDevil]

the question was why copper was reduced and not nitrate. It is mainly kinetics, if you come across a good catalyst for nitrate reduction, please let me know!

[Nobby]

the question was why copper was reduced and not nitrate

Thats right.

Zinc in alkaline solution is able to reduce Nitrat down to Ammonia. But this is an other story.

[DevaDevil]

zinc would be oxidised. This is not a catalyst, it is a sacrifice. Pt can reduce nitrate in acid solutions, at moderate overpotentials, to ammonia as well, but I would prefer to reduce it to nitrogen