The nitric acid It is an inorganic compound consisting of a nitrogen oxo acid. It is considered a strong acid, although its pKa (-1.4) is similar to the pKa of the hydronium ion (-1.74). From this point on, it is perhaps the "weakest" of many known strong acids..
Its physical appearance consists of a colorless liquid that on storage changes to a yellowish color, due to the formation of nitrogen gases. Its chemical formula is HNO3.
It is somewhat unstable, undergoing slight decomposition from exposure to sunlight. In addition, it can be completely decomposed by heating, giving rise to nitrogen dioxide, water and oxygen..
The image above shows some nitric acid contained in a volumetric flask. You can notice its yellow coloration, indicative of a partial decomposition.
It is used in the manufacture of inorganic and organic nitrates, as well as in nitroso compounds that are used in the manufacture of fertilizers, explosives, intermediate agents for dyes and different organic chemical compounds..
This acid was already known to the alchemists of the 8th century, which they called “agua fortis”. The German chemist Johan Rudolf Glauber (1648) designed a method for its preparation, which consisted of heating potassium nitrate with sulfuric acid.
It is prepared industrially following the method designed by Wilhelm Oswald (1901). The method, in general lines, consists of the catalytic oxidation of ammonium, with the successive generation of nitric oxide and nitrogen dioxide to form nitric acid..
In the atmosphere, NOtwo produced by human activity reacts with cloud water, forming HNO3. Then, during acid rains, it precipitates together with drops of water, eating away, for example, statues in public squares..
Nitric acid is a very toxic compound, and continuous exposure to its vapors can lead to chronic bronchitis and chemical pneumonia..
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The upper image shows the structure of an HNO molecule.3 with a model of spheres and bars. The nitrogen atom, the blue sphere, is located in the center, surrounded by a trigonal plane geometry; however, the triangle is distorted by one of its longest vertices.
Nitric acid molecules are then flat. The N = O, N-O, and N-OH bonds make up the vertices of the flat triangle. If observed in detail, the N-OH bond is more elongated than the other two (where the white sphere representing the H atom is found).
There are two bonds that are the same length: N = O and N-O. This fact goes against the valence bond theory, where double bonds are predicted to be shorter than single bonds. The explanation for this lies in the phenomenon of resonance, as seen in the image below.
Both bonds, N = O and N-O, are therefore equivalent in terms of resonance. This is represented graphically in the structure model by using a dashed line between two O atoms (see structure).
When HNO is deprotonated3, the stable anion nitrate NO is formed3-. In it, the resonance now involves all three O atoms. This is the reason why HNO3 has high Bronsted-Lowry acidity (H ion donor species+).
-Nitric acid
-Azotic acid
-Hydrogen nitrate
-Fortis water.
63.012 g / mol.
Colorless or pale yellow liquid, which may turn reddish brown.
Pungent, suffocating characteristic.
181ºF to 760mmHg (83ºC).
-41.6 ºC.
Very soluble and miscible with water.
1.513 g / cm3 at 20 ºC.
1.50 (in relation to water = 1).
2 or 3 times estimated (in relation to air = 1).
63.1 mmHg at 25 ºC.
On exposure to atmospheric moisture or heat, it can decompose to form nitrogen peroxide. When heated to decomposition, it emits a very toxic fume of nitrogen oxide and hydrogen nitrate..
Nitric acid is not stable, and can decompose in contact with heat and exposure to sunlight, and emitting nitrogen dioxide, oxygen and water..
1,092 mPa at 0 ° C, and 0.617 mPa at 40 ° C.
It is capable of attacking all base metals, except aluminum and chromic steel. Attacks some of the varieties of plastics, rubbers, and coatings. It is a caustic and corrosive substance, so it must be handled with extreme caution.
39.1 kJ / mol at 25 ºC.
-207 kJ / mol (298 ºF).
146 kJ / mol (298 ºF).
-0.04356 N / m at 0 ºC
-0.04115 N / m at 20 ºC
-0.0376 N / m at 40 ºC
-Low odor: 0.75 mg / m3
-High odor: 250 mg / m3
-Irritating concentration: 155 mg / m3.
pKa = -1.38.
1.393 (16.5 ºC).
-Can form solid hydrates, such as HNO3∙ HtwoO and HNO3∙ 3HtwoOr: "nitric ice".
Nitric acid is a strong acid that ionizes rapidly in water as follows:
HNO3 (l) + HtwoO (l) => H3OR+ (ac) + NO3-
Reacts with basic oxides to form a nitrate salt and water.
CaO (s) + 2 HNO3 (l) => Ca (NO3)two (ac) + HtwoO (l)
Likewise, it reacts with bases (hydroxides), forming a salt of nitrate and water..
NaOH (aq) + HNO3 (l) => NaNO3 (ac) + HtwoO (l)
And also with carbonates and acid carbonates (bicarbonates), also forming carbon dioxide.
NatwoCO3 (ac) + HNO3 (l) => NaNO3 (ac) + HtwoO (l) + COtwo (g)
Nitric acid can also behave as a base. For this reason, it can react with sulfuric acid.
HNO3 + 2HtwoSW4 <=> NOTtwo+ + H3OR+ + 2HSO4-
Nitric acid undergoes autoprotolysis.
2HNO3 <=> NOTtwo+ + NOT3- + HtwoOR
In the reaction with metals, nitric acid does not behave like strong acids, which react with metals, forming the corresponding salt and releasing hydrogen in gaseous form..
However, magnesium and manganese react hot with nitric acid, just as the other strong acids do..
Mg (s) + 2 HNO3 (l) => Mg (NO3)two (ac) + Htwo (g)
Nitric acid reacts with metal sulphites to form a nitrate salt, sulfur dioxide and water..
NatwoSW3 (s) + 2 HNO3 (l) => 2 NaNO3 (ac) + SOtwo (g) + HtwoO (l)
And it also reacts with organic compounds, substituting a hydrogen for a nitro group; thus constituting the basis for the synthesis of explosive compounds such as nitroglycerin and trinitrotoluene (TNT).
It is produced at an industrial level through the catalytic oxidation of ammonium, according to the method described by Oswald in 1901. The procedure consists of three stages or steps.
Ammonia is oxidized by oxygen in the air. The reaction is carried out at 800 ºC and at a pressure of 6-7 atm, with the use of platinum as a catalyst. Ammonium is mixed with air with the following ratio: 1 volume of ammonia per 8 volumes of air.
4NH3 (g) + 5Otwo (g) => 4NO (g) + 6HtwoO (l)
Nitric oxide is produced in the reaction, which is taken to the oxidation chamber for the next stage..
The oxidation is carried out by the oxygen present in the air at a temperature below 100 ºC.
2NO (g) + Otwo (g) => 2NOtwo (g)
In this stage the formation of nitric acid occurs.
4NOtwo + 2HtwoO + Otwo => 4HNO3
There are several methods for the absorption of nitrogen dioxide (NOtwo) in water.
Among other methods: NOtwo is dimerized to NtwoOR4 at low temperatures and high pressure, in order to increase its solubility in water and produce nitric acid.
3NtwoOR4 + 2HtwoO => 4HNO3 + 2NO
The nitric acid produced by the oxidation of ammonia has a concentration between 50-70%, which can be brought to 98% by using concentrated sulfuric acid as a dehydrating agent, allowing the concentration of nitric acid to be increased..
Thermal decomposition of copper (II) nitrate, producing nitrogen dioxide and oxygen gases, which are passed through water to form nitric acid; as in the Oswald method, previously described.
2Cu (NO3)two => 2CuO + 4NOtwo + ORtwo
Reaction of a nitrate salt with HtwoSW4 concentrated. The nitric acid formed is separated from the HtwoSW4 by distillation at 83 ° C (boiling point of nitric acid).
KNO3 + HtwoSW4 => HNO3 + KHSO4
60% of nitric acid production is used in the manufacture of fertilizers, especially ammonium nitrate.
This is characterized by its high concentration of nitrogen, one of the three main plant nutrients, the nitrate being used immediately by the plants. Meanwhile, ammonia is oxidized by the microorganisms present in the soil, and is used as a long-term fertilizer..
-15% of nitric acid production is used in the manufacture of synthetic fibers.
-It is used in the production of nitric acid esters and nitro derivatives; such as nitrocellulose, acrylic paints, nitrobenzene, nitrotoluene, acrylonitriles, etc..
-It can add nitro groups to organic compounds, and this property can be used to make explosives such as nitroglycerin and trinitrotoluene (TNT)..
-Adipic acid, a precursor to nylon, is produced on a large scale by the oxidation of cyclohexanone and cyclohexanol by nitric acid..
Nitric acid, due to its oxidizing capacity, is very useful in the purification of metals present in minerals. Likewise, it is used in the obtaining of elements such as uranium, manganese, niobium, and zirconium, and in the acidification of phosphoric rocks to obtain phosphoric acid..
It is mixed with concentrated hydrochloric acid to form "aqua regia". This solution is capable of dissolving gold and platinum, which allows its use in the purification of these metals..
Nitric acid is used to obtain an antique effect in furniture made with pine wood. Treatment with a 10% nitric acid solution produces a gray-gold color in the wood of the furniture.
-The mixture of aqueous solutions of nitric acid 5-30% and phosphoric acid 15-40% is used in the cleaning of the equipment used in the milking work, in order to eliminate the residues of the precipitates of the magnesium and calcium compounds..
-It is useful in cleaning glassware used in the laboratory.
-Nitric acid has been used in photography, specifically as an additive to ferrous sulfate developers in the wet plate process, in order to promote a whiter color in ambrotypes and tintypes..
-It was used to lower the pH of the silver bath of the collodion plates, which allowed to obtain a reduction in the appearance of a mist that interfered with the images.
-Due to its solvent capacity, it is used in the analysis of different metals by flame atomic absorption spectrophotometry techniques, and inductively coupled plasma mass spectrophotometry..
-The combination of nitric acid and sulfuric acid was used for the conversion of common cotton into cellulose nitrate (nitric cotton).
-The drug Salcoderm for external use is used in the treatment of benign neoplasms of the skin (warts, corns, condylomas and papillomas). It possesses properties of cauterization, relief of pain, irritation and itching. Nitric acid is the main component of the drug formula.
-Red fuming nitric acid, and white fuming nitric acid, are used as oxidants for liquid rocket fuels, especially in the BOMARC missile..
-In contact with the skin, it can cause skin burns, severe pain and dermatitis..
-In contact with the eyes it can cause severe pain, tearing and in severe cases, corneal damage and blindness..
-Inhalation of the vapors can cause coughing, respiratory distress, causing nosebleeds, laryngitis, chronic bronchitis, pneumonia and pulmonary edema in severe or chronic exposures..
-Due to its ingestion, there is lesions in the mouth, salivation, intense thirst, pain to swallow, intense pain in the entire digestive tract and risk of perforation of the wall of the same.
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