In dilute solution, in the absence of Oxygen, Nitrogen Monoxide is produced. If you allow air in, it will react with oxygen in the air to produce Nitrogen Dioxide which, when reacted with Sodium Hydroxide produces Sodium Nitrate.
If you keep out air, it will form sodium Nitrite.
http://www.freepatentsonline.com/3965247.html
It is well known that if nitrous gases, i.e. gases containing nitric oxide and nitrogen dioxide, are brought into contact with alkaline aqueous solutions, the nitric oxide and nitrogen dioxide will be absorbed with the formation of nitrites and nitrates. See U.S. Pat. Nos. 1,903,815 and 1,978,431. Such gases are typically obtained from a wide variety of sources, as for example, by the arc process of nitrogen fixation, by the air-oxidation of ammonia or as waste gases from an absorption process of which nitric acid is the primary product. By controlling the ratio of nitric oxide and nitrogen dioxide so that more nitric oxide than nitrogen dioxide is present in the gas feed, the amount of nitrates that is formed can be minimized, thereby allowing maximum conversion of the nitrogen oxide to the nitrites.
In such processes nitrous gases are contacted for absorption in one or more stages with a liquid medium maintained alkaline by the presence of suitable alkaline reacting agents, e.g. sodium hydroxide, sodium carbonate, sodium bicarbonate and mixtures thereof. The liquor, herein termed the "final absorption liquor", which is separated from the last absorption stage contains dissolved sodium nitrite together with sodium nitrate and minor amounts of unreacted alkaline reacting agent. Further, use of a nitrous gas feed containing carbon dioxide will also cause the finished absorption liquor to contain sodium carbonate/bicarbonate values due to the absorption of CO 2 in the aqueous medium.
http://en.wikipedia.org/wiki/Nitrogen_oxide
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In the presence of excess oxygen (O2), nitric oxide (NO) will be converted to nitrogen dioxide (NO2), with the time required dependent on the concentration in air as shown below:[1]
NO concentration in air
(ppm)
Time required for half NO
to be oxidized to NO2 (min)
20,000 0.175
10,000 0.35
1,000 3.5
100 35
10 350
1 3500
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Mono-nitrogen oxides eventually form nitric acid when dissolved in atmospheric moisture, forming a component of acid rain. The following chemical reaction occurs when nitrogen dioxide reacts with water:
2NO2 + H2O → HNO2 + HNO3 (nitrogen dioxide + water → nitrous acid + nitric acid).
Nitrous acid then decomposes as follows:
3HNO2 → HNO3 + 2NO + H2O (nitrous acid → nitric acid + nitric oxide + water),
where nitric oxide will oxidize to form nitrogen dioxide that again reacts with water, ultimately forming nitric acid:
4NO + 3O2 + 2H2O → 4HNO3 (nitric oxide + oxygen + water → nitric acid).
