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Concentrated Nitric Acid is unstable. When exposed to light or heat, it decomposes and releases nitrogen dioxide. The decomposed nitrogen dioxide dissolves in nitric acid, thus giving a light-yellow appearance. But dilute nitric acid is relatively stable.
Reaction equation: 4HNO = illumination = 4NO_ + O + 2H_O
4HNOtamping= = 4NO tamping_+Otamping_+2H tamping O
Esterification (strong acidity)
Nitric Acid can esterify with alcohols to produce corresponding nitrate esters. In the past, nitric acid participated in esterification reaction was considered to produce carbon cationic intermediates. However, many literatures described the mechanism as Fischer esterification, i.e. "acid dehydroxyl alcohol dehydrogenation" has the same esterification mechanism as carboxylic acid.
Nitric acid can be completely ionized in aqueous solution, producing a large number of hydrogen ions:
As the highest valence (+5) hydrate of nitrogen element, nitric acid has strong acidity. Generally speaking, the aqueous solution of nitric acid is completely ionized. Nitric acid can be esterified with alcohols, such as the preparation of nitroglycerin. (Actually, we use concentrated sulfuric acid to produce a lot of NO2), which is cheaper and easier to handle. With other stronger dehydrants, such as P4O10, we can also produce a lot of nitryl cations, which is the essence of nitration.
Esterification of nitric acid is used to produce nitrocellulose. The equation is as follows:
3nHNO 3+ [C6H7O 2(OH)3]n-[C6H7O 2(O-NO2)3]n+3nH 2
For the production of nitroglycerin, see the following equation:
Concentrated nitric acid or fuming nitric acid mixed with dehydrating agent (concentrated sulfuric acid, phosphorus pentoxide) can be used as nitrating reagent to initiate nitrification of some compounds. The nitration reaction belongs to electrophilic substitution. The electrophilic reagent in the reaction is nitrate ion. The dehydrating agent is beneficial to the production of nitrate ion.
The most common nitration reaction is benzene nitration:
This reaction is often used to produce 2,4,6-trinitrotoluene (TNT).
Nitrogen in Nitric Acid molecule is the highest valence (+5), so nitric acid has strong oxidation. Its reduction products vary with the concentration of nitric acid. Generally speaking, the higher the concentration of nitric acid, the fewer electrons per molecule of nitric acid. The reduction products of concentrated nitric acid are mainly nitrogen dioxide, dilute nitric acid is mainly nitric oxide, and the thinner nitric acid can be reduced to dioxide. Nitrogen, nitrogen, ammonium nitrate and so on, it should be pointed out that the above products are only dominant products. In fact, with the reaction proceeding, the concentration of nitric acid gradually decreases, and all reduction products may appear.
HNO 3-0.803_NO2-1.07_HNO 2-0.983_NO-1.591_N2O-1.77_N2-0.27_NH 4+
HNO 3-0.88_NH 4+
Concentrated nitric acid:
Dilute nitric acid:
Very dilute nitric acid:
Extremely dilute nitric acid:
1. Pure nitric acid can be self-ionized:
2. Because of the strong oxidation of nitric acid, hydrogen cannot be produced by nitric acid. As soon as hydrogen ions are replaced from nitric acid to hydrogen, they are oxidized by nitrate ions.
The principle is right:
(Concentrated nitric acid)
(Dilute nitric acid)
3. The strong oxidation of nitric acid does not come from nitrate ion (nitrate ion itself has no oxidation), but from nitrate ion under acidic conditions. (e.g., adding hydrochloric acid in ferrous nitrate solution, the color of the solution changes from green to yellow, adding potassium thiocyanate solution, and the solution turns to blood red. It is proved that ferrous ions are oxidized to iron ions again.
4. The oxidation of nitric acid is proportional to its concentration. Dilute nitric acid reacts with metal to produce nitric oxide. Concentrated nitric acid reacts with metal to produce nitric oxide, but the oxidizing ability of concentrated nitric acid is stronger than that of dilute nitric acid. Nitric oxide is oxidized to nitrogen dioxide by nitrate ion in the presence of hydrogen ion. The equation is as follows:
Hydrogen iodide reacts with nitric acid of different concentration to oxidize iodine ions into iodine and iodate ions respectively:
(Dilute nitric acid)
(Concentrated nitric acid)
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