strong monobasic acid, which is a standard condition colorless liquid which turns yellow upon storage can be in a solid state, characterized by two crystalline modifications (monoclinic or orthorhombic lattice), at temperatures below minus 41.6 ° C.This substance with the chemical formula - HNO3 - nitric acid is called.It has a molar mass of 63.0 g / mol, and it corresponds to the density of 1.51 g / cc.The boiling point of the acid equal to 82.6 ° C, accompanied by a process of decomposition (partial): 4HNO3 → 2H2O + 4NO2 + O2.Acid solution with a mass fraction of the basic substance to be 68% boils at a temperature of 121 ° C.The refractive index of the pure substance corresponds to 1,397.Acid can be mixed with water in any ratio and, being a strong electrolyte almost completely dissociate into ions H + and NO3-.Solid form - trihydrate and monohydrate having the formula: HNO3 • 3H2O • HNO3 and H2O, respectively.
Nitric acid - corrosive, toxic substances and strong oxidizer.From the Middle Ages known the name, as "strong water» (Aqua fortis).Alchemists who discovered acid in the 13th century, was given the name, make sure it is unusual properties (corroded all metals except gold), surpassing a million times the power of acetic acid, which in those days was considered the most active.But even after three centuries it has been found that corrode, even gold can be a mixture of acids such as nitric and hydrochloric acid in a volume ratio of 1: 3, which for this reason called "aqua regia".The appearance of a yellow tint upon storage due to the accumulation of nitrogen oxides therein.Sales acid more often with a concentration of 68%, while the content of the basic substance more than 89% it is called "fuming".
chemical properties of nitric acid differentiate it from a dilute sulfuric or hydrochloric acid that HNO3 stronger oxidant, so never released hydrogen in reactions with metals.Through oxidative properties as it reacts with many non-metals.And in both cases is always formed nitrogen dioxide NO2.The redox reduction reaction of nitrogen occurs to varying degrees: HNO3, NO2, N2O3, NO, N2O, N2, NH3, which is determined by the acid concentration and the activity of the metal.The molecules of the compounds formed contains nitrogen in oxidation state +5, +4, +3, +2, +1, 0, 3, respectively.For example, copper is oxidized with concentrated acid to copper nitrate (II): Cu + 4HNO3 → 2NO2 + Cu (NO3) 2 + 2H2O, and phosphorus - up metaphosphoric acid: P + 5HNO3 → 5NO2 + 2H2O + HPO3.
otherwise dilute nitric acid reacts with non-metals.For example, reaction with phosphorus: 3P + 5HNO3 + 2H2O → 3H3PO4 + 5NO seen that nitrogen is reduced to the ferrous state.This produces carbon monoxide, nitrogen and phosphorus is oxidized to phosphoric acid.Concentrated nitric acid in a mixture of hydrochloric acid dissolves the gold: Au + 4HCl + HNO3 → NO + H [AuCl4] + 2H2O and platinum: 3Pt + 18HCl + 4HNO3 → 4NO + 3H2 [PtCl6] + 8H2O.In these reactions, initially, hydrochloric acid is oxidized with nitric separation of chlorine, and then form a complex metal chlorides.
Nitric acid is obtained on an industrial scale in three main ways:
- first - reacting salts of sulfuric acid: H2SO4 + NaNO3 → HNO3 + NaHSO4.Previously, it was the only method, but with the advent of other technologies, currently it is used under laboratory conditions to produce acid fuming.
- second - is the arc method.While blowing air through the electric arc with a temperature of 3000 to 3500 ° C, part of the nitrogen in the air reacts with the oxygen, forming carbon monoxide, nitrogen: N2 + O2 → 2NO, which after cooling is oxidized to nitrogen dioxide (high temperature monoxide with oxygen does not interact): O2 + 2NO → 2NO2.Then, virtually all the nitrogen dioxide with an excess of oxygen dissolved in the water: 2H2O + O2 → 4NO2 + 4HNO3.
- third - this ammonia method.Ammonia is oxidized at a platinum catalyst to nitrogen monoxide: 4NH3 + 5O2 → 4NO + 6H2O.The resulting nitrous gases are cooled, and the formed nitrogen dioxide, which is absorbed by water.By this method, the acid concentration from 60 to 62%.
Nitric acid is widely used in industry for the preparation of medicaments, dyes, explosives, nitric fertilizers and nitric acid salts.In addition, it is used for the dissolution of metals (e.g., copper, lead, silver) that does not react with other acids.The jewelry business is used to determine gold alloy (this is the main method).
