AJKOER
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Reaction of Chlorine water treated with NO2 & O2
I would appreciate some feedback on treating Chlorine water with selective small doses of NO2 and O2. Expected reactions:
1. 4 Cl2 + 4 H2O <-> 4 HCl + 4 HOCl
2. 2 NO2 + 4 HCl --> 2 Cl2 + 2 H2O + 2 NO (See http://books.google.com/books?id=zVIpX7rkk7oC&pg=PA14&am... )
3. 2 NO + O2 --> 2 NO2
so reactions (2) and (3) performed together implies:
4. 4 HCl + O2 ---2 NO2---> 2 Cl2 + 2 H2O
However, all of the NO2 catalyst could be consumed by the HOCl via the reaction:
5. 2 NO2 + H2O + HOCl --> 2 HNO3 + HCl (see http://books.google.com/books?id=8cv36t8mOEwC&pg=PA122&a... )
But, as these as simultaneous reactions in Chlorine water, if reactions (4) and (5) do not occur at the same speed (opinion on which is faster) some
of the HCl can be reduced before all the NO2 is consumed by the HOCl. Am I correct?
Differences in speed means that one may be able to apply timed small doses of NO2.
[Edited on 30-1-2013 by AJKOER]
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AJKOER
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The reference above equation (x) notes (see http://books.google.com/books?id=zVIpX7rkk7oC&pg=PA15&am... , page 15:
2 HCl + H2O2 ---27 to 60 C---> 2 H2O + Cl2
so I would speculate that the reaction:
4 HCl + O2 ---2 NO2---> 2 Cl2 + 2 H2O
occurs above room temperature while
2 NO2 + H2O + HOCl --> 2 HNO3 + HCl
occurs naturally in the atmosphere (at a lower temperature). See http://144.206.159.178/ft/166/85929/1452453.pdf ,page 1350.
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woelen
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I have actually done some experimenting with Cl2 and NOx.
Cl2 and NO give orange gaseous ONCl, which quickly hydrolyses in water, but not in concentrated HCl. In the latter it dissolves, giving very nice
orange solutions, looking very much like solutions of K2Cr2O7. ONCl reacts with water, giving HCl and HNO2, which in turn gives HNO3 and NO.
Dry Cl2 and NO2 do not seem to react. The mix of gases becomes brown, not looking very nice. On addition of water, however, the mix of gases quickly
dissolves and a colorless acidic solution is obtained. I tested this and it contains chloride. The other part most likely is nitric acid. I am quite
sure that the reaction is as follows:
2NO2 + Cl2 + 2H2O --> 2HNO3 + 2HCl
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AndersHoveland
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Quote: Originally posted by woelen  | | Cl2 and NO give orange gaseous ONCl, which quickly hydrolyses in water, but not in concentrated HCl. In the latter it dissolves, giving very nice
orange solutions, looking very much like solutions of K2Cr2O7. ONCl reacts with water, giving HCl and HNO2, which in turn gives HNO3 and NO.
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It is obviously in equilibrium.
Nitric and hydrochloric acids in concentrated solution have equilibrium with nitrosyl chloride and chlorine:
HNO3 + 3 HCl <==> 2 H2O + NOCl + Cl2
This is the same equilibrium that allows aqua regia to dissolve gold. The reaction shifts to the left in more dilute aqueous solution, or to the right
in more concentrated acidic solutions.
Since nitrosyl chloride does indeed hydrolyze in water to HNO2 and HCl, the equilibrium could also be written as:
HNO3 + 2 HCl <==> HNO2 + H2O + Cl2
If I recall correctly, aqueous solutions of nitrogen dioxide are in equilibrium with nitric acid and nitric oxide. The equilibrium can shift either
way depending on conditions.
3 NO2 + H2O <==> 2 HNO3(aq) + NO
2 HNO2 <==> H2O + NO2 + NO
So we could also write the equilibrium as:
4 HNO3 + 8 HCl <==> 2 NO2 + 2 NOCl + 6 H2O + 3 Cl2
Obviously nitric oxide is not going to be able to accumulate in the presence of chlorine, since it will just be immediately oxidized.
In the absence of water (or also as Woelen has demonsrated in conc. HCl) nitric oxide is oxidized by chlorine to nitrosyl chloride. In more dilute
aqueous solutions, chlorine oxidizes it to nitric acid.
2 NO + Cl2 --> 2 NOCl
NO + 2 H2O + 1½ Cl2 --> HNO3(aq) + 3 HCl(aq)
Chlorine can similarly oxidize nitrogen dioxide to nitric acid even if there is no O2 present.
2 NO2 + 2 H2O + Cl2 --> 2 HNO3(aq) + 2 HCl(aq)
Probably the reaction could also go in reverse if, for example, hydrogen chloride gas were being passed into very concentrated nitric acid.
Note in many of these reactions I have written (aq), meaning "aqueous". This is significant because the reactivity of both nitric acid and
hydrochloric acid depends on whether there is additional water present. In dilute solution nitric acid exists as nitrate ions and hydronium ions,
H3O+. In very concentrated solutions nitric acid is able to protonate itself, which is where the nitronium ions come from during
nitration reactions.
One interesting experiment may be to continuosly bubble in air into a solution of sodium nitrate and 20% hydrochloric acid. Because of the small
equilibrium with nitrous acid / nitric oxide, the air should be able to oxidize some of the hydrochloric acid to chlorine. Effectively, the sodium
nitrate would serve as a catalyst.
[Edited on 1-2-2013 by AndersHoveland]
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AndersHoveland
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Nitric acid can also be made by reacting dry anhydrous hydrogen chloride gas with dry nitrogen dioxide. (the HCl is dried by being passed through
baked CaCl2 powder)
The reactions are:
HCl + (2)NO2 --> HNO3 + NOCl
(4)HCl + (2)NO2 --> (2)H2O + NOCl
where the first is the primary reaction, and the second is the limiting reaction.
This procedure will yield fuming red nitric acid of a certain concentration, which is probably somewhere between 70-85%.
see also US 4557920
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blogfast25
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| Quote: Originally posted by woelen | | Cl2 and NO give orange gaseous ONCl, which quickly hydrolyses in water, but not in concentrated HCl. In the latter it dissolves, giving very nice
orange solutions, looking very much like solutions of K2Cr2O7. |
Which is what good quality concentrated Aqua Regia looks like...
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