Preparation and Reactions
Nitrogen dioxide typically arises via the oxidation of nitric oxide by oxygen in air:
- 2 NO + O2 → 2 NO2
In the laboratory, NO2 can be prepared in a two step procedure by thermal decomposition of dinitrogen pentoxide, which is obtained by dehydration of nitric acid:
- 2 HNO3 → N2O5 + H2O
- 2 N2O5 → 4 NO2 + O2
The thermal decomposition of some metal nitrates also affords NO2:
- 2 Pb(NO3)2 → 2 PbO + 4 NO2 + O2
Alternatively, reduction of concentrated nitric acid by metal (such as copper).
- 4 HNO3 + Cu → Cu(NO3)2 + 2 NO2 +2 H2O
Or finally by adding concentrated nitric acid over tin. Stannic acid is produced as byproduct.
- 4HNO3 + Sn → H2O + H2SnO3 + 4 NO2
Read more about this topic: Nitrogen Dioxide
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