Decomposition of nitrous acid in aqueous solution. Salts of nitric and nitrous acids
Nitrous acid is a monobasic weak acid that can only exist in dilute blue aqueous solutions and in gaseous form. Salts of this acid are called nitrites or nitrites. They are toxic and more stable than the acid itself. Chemical formula of this substance looks like this: HNO2.
Physical properties:
1. Molar mass equal to 47 g/mol.
2. is equal to 27 a.m.u.
3. Density is 1.6.
4. The melting point is 42 degrees.
5. The boiling point is 158 degrees.
Chemical properties nitrous acid s
1. If a solution with nitrous acid is heated, the following chemical reaction will occur:
3HNO2 (nitrous acid) \u003d HNO3 (nitric acid) + 2NO is released as a gas) + H2O (water)
2. Dissociates in aqueous solutions and is easily displaced from salts by stronger acids:
H2SO4 (sulphuric acid) + 2NaNO2 (sodium nitrite) = Na2SO4 (sodium sulfate) + 2HNO2 (nitrous acid)
3. The substance we are considering can exhibit both oxidizing and reducing properties. When exposed to stronger oxidizing agents (for example: chlorine, hydrogen peroxide H2O2, oxidizes to nitric acid (in some cases, a salt of nitric acid is formed):
Restorative properties:
HNO2 (nitrous acid) + H2O2 (hydrogen peroxide) = HNO3 (nitric acid) + H2O (water)
HNO2 + Cl2 (chlorine) + H2O (water) = HNO3 (nitric acid) + 2HCl (hydrochloric acid)
5HNO2 (nitrous acid) + 2HMnO4 \u003d 2Mn (NO3) 2 (manganese nitrate, nitric acid salt) + HNO3 (nitric acid) + 3H2O (water)
Oxidizing properties:
2HNO2 (nitrous acid) + 2HI = 2NO (oxygen oxide, as gas) + I2 (iodine) + 2H2O (water)
Obtaining nitrous acid
This substance can be obtained in several ways:
1. When dissolving nitrogen oxide (III) in water:
N2O3 (nitric oxide) + H2O (water) = 2HNO3 (nitrous acid)
2. When dissolving nitrogen oxide (IV) in water:
2NO3 (nitric oxide) + H2O (water) = HNO3 (nitric acid) + HNO2 (nitrous acid)
Application of nitrous acid:
- diazotization of aromatic primary amines;
- production of diazonium salts;
- in synthesis organic matter(for example, for the production of organic dyes).
The effect of nitrous acid on the body
This substance is toxic, has a bright mutagenic effect, since in essence it is a deaminating agent.
What are nitrites
Nitrites are various salts of nitrous acid. They are less resistant to temperature than nitrates. Needed in the production of some dyes. Used in medicine.
Sodium nitrite has gained particular importance for humans. This substance has the formula NaNO2. It is used as a preservative in the food industry in the production of fish and meat products. It is a powder of pure white or slightly yellowish color. Sodium nitrite is hygroscopic (with the exception of purified sodium nitrite) and highly soluble in H2O (water). In air, it is able to gradually oxidize to have strong reducing properties.
Sodium nitrite is used in:
- chemical synthesis: to obtain diazo-amine compounds, to deactivate excess sodium azide, to obtain oxygen, sodium oxide and sodium nitrogen, to absorb carbon dioxide;
- in production food products(food additive E250): as an antioxidant and antibacterial agent;
- in construction: as an antifreeze additive to concrete in the manufacture of structures and building products, in the synthesis of organic substances, as an atmospheric corrosion inhibitor, in the production of rubbers, poppers, additive solution for explosives; when processing metal to remove the tin layer and during phosphating;
- in photography: as an antioxidant and reagent;
- in biology and medicine: vasodilator, antispasmodic, laxative, bronchodilator; as an antidote for animal or human poisoning with cyanide.
Other salts of nitrous acid (eg potassium nitrite) are also currently used.
Nitric acid. Pure nitric acid HNO 3 is a colorless liquid with a density of 1.51 g / cm at - 42 ° C, solidifying into a transparent crystalline mass. In the air, it, like concentrated hydrochloric acid, "smokes", since its vapors form small droplets of fog with "moisture in the air,
Nitric acid does not differ in strength, Already under the influence of light, it gradually decomposes:
The higher the temperature and the more concentrated acid, the faster the decomposition. The released nitrogen dioxide dissolves in the acid and gives it a brown color.
Nitric acid is one of the strongest acids; in dilute solutions, it completely decomposes into H + and - NO 3 ions.
Oxidizing properties of nitric acid. A characteristic property of nitric acid is its pronounced oxidizing ability. Nitric acid-one
of the most energetic oxidizers. Many non-metals are easily oxidized by it, turning into the corresponding acids. So, when sulfur is boiled with nitric acid, it gradually oxidizes into sulfuric acid, phosphorus into phosphoric acid. A smoldering ember immersed in concentrated HNO 3 flares up brightly.
Nitric acid acts on almost all metals (with the exception of gold, platinum, tantalum, rhodium, iridium), turning them into nitrates, and some metals into oxides.
Concentrated HNO 3 passivates some metals. Lomonosov also discovered that iron, which dissolves easily in dilute nitric acid, does not dissolve.
in cold concentrated HNO 3 . Later it was found that nitric acid has a similar effect on chromium and aluminum. These metals go under
the action of concentrated nitric acid in a passive state.
The degree of oxidation of nitrogen in nitric acid is 4-5. Acting as an oxidizing agent, HNO 3 can be reduced to various products:
Receipt.
1. In the laboratory, nitric acid is obtained by reacting anhydrous nitrates with concentrated sulfuric acid:
Ba (NO 3) 2 + H 2 SO 4 → BaSO 4 ↓ + 2HNO 3.
2. In industry, the production of nitric acid goes in three stages:
1. Oxidation of ammonia to nitric oxide (II):
4NH 3 + 5O 2 → 4NO + 6 H 2 O
2. Oxidation of nitric oxide (II) to nitric oxide (IV):
2NO + O 2 → 2NO 2
3. Dissolution of nitric oxide (IV) in water with excess oxygen:
4NO 2 + 2H 2 O + O 2 → 4HNO 3
Chemical properties . Shows all the properties of acids. Nitric acid is one of the strongest mineral acids.
1. In aqueous solutions, it is completely dissociated into ions:
HNO 3 → H + + NO - 3
2. Reacts with metal oxides:
MgO + 2HNO 3 → Mg (NO 3) 2 + H 2 O,
3. Reacts with bases:
Mg (OH) 2 + 2HNO 3 → Mg (NO 3) 2 + 2H 2 O,
4. Concentrated HNO 3, when interacting with the most active metals to Al, is reduced to N 2 O. For example:
4Ca + 10HNO 3 → 4Ca(NO 3) 2 + N 2 O+ 5H 2 O
5. Concentrated HNO 3 when interacting with less active metals (Ni, Cu, Ag, Hg) is reduced to NO 2. For instance:
4HNO 3 + Ni → Ni(NO 3) 2 + 2NO 2 + 2H 2 O.
6. Similarly, concentrated HNO 3 reacts with non-metals. The non-metal is oxidized. For instance:
5HNO 3 + Po → HP + 5O 3 + 5NO 2 + 2H 2 O.
C nitric acid olis - nitrates when heated, they decompose according to the scheme:
to the left of Mg: MeNO 3 → MeNO 2 + O 2
Mg - Cu: MeNO 3 → MeO + NO 2 + O 2
to the right Cu MeNO 3 → Me + NO 2 + O 2
Application.
Nitric acid is used to produce nitrogen fertilizers, medicinal and explosives.
Hydrogen. The structure of the atom, physical and chemical properties, the production and use of hydrogen.
HYDROGEN, H, chemical element with atomic number 1, atomic mass 1.00794.
Natural hydrogen consists of a mixture of two stable nuclides with mass numbers 1.007825 (99.985% in the mixture) and 2.0140 (0.015%). In addition, in natural hydrogen there are always negligible amounts of a radioactive nuclide - tritium 3 H (half-life T1 / 2 = 12.43 years). Since the nucleus of a hydrogen atom contains only 1 proton (there cannot be less protons in the nucleus of an atom), it is sometimes said that hydrogen forms the natural lower boundary of the periodic system of elements of D. I. Mendeleev (although the element hydrogen itself is located in the uppermost part tables). The element hydrogen is located in the first period of the periodic table. It belongs to the 1st group (group IA alkali metals), and to the 7th group (group VIIA of halogens).
The masses of atoms in hydrogen isotopes differ greatly (by several times). This leads to noticeable differences in their behavior in physical processes (distillation, electrolysis, etc.) and to certain chemical differences (differences in the behavior of isotopes of one element are called isotope effects; for hydrogen, isotope effects are most significant). Therefore, unlike the isotopes of all other elements, hydrogen isotopes have special symbols and names. Hydrogen with a mass number of 1 is called light hydrogen, or protium (lat. Protium, from the Greek protos - the first), denoted by the symbol H, and its nucleus is called a proton, symbol p. Hydrogen with a mass number of 2 is called heavy hydrogen, deuterium (Latin Deuterium, from the Greek deuteros - the second), the symbols 2 H, or D (read "de") are used to designate it, the nucleus d is the deuteron. A radioactive isotope with a mass number of 3 is called superheavy hydrogen, or tritium (lat. Tritum, from the Greek tritos - the third), the symbol 3 H or T (read "those"), the nucleus t is a triton.
The configuration of the only electron layer of the neutral unexcited hydrogen atom is 1s1. In compounds, it exhibits oxidation states +1 and, less often, -1 (valency I). The radius of the neutral hydrogen atom is 0.0529 nm. The ionization energy of the atom is 13.595 eV, the electron affinity is 0.75 eV. On the Pauling scale, the electronegativity of hydrogen is 2.20. Hydrogen is one of the non-metals.
In its free form, it is a light, flammable gas without color, odor or taste.
Physical and chemical properties: at normal conditions hydrogen is a light (density under normal conditions 0.0899 kg / m 3) colorless gas. Melting point -259.15°C, boiling point -252.7°C. Liquid hydrogen (at the boiling point) has a density of 70.8 kg/m 3 and is the lightest liquid. The standard electrode potential H 2 / H– in an aqueous solution is taken equal to 0. Hydrogen is poorly soluble in water: at 0 ° C, the solubility is less than 0.02 cm 3 / ml, but it is highly soluble in some metals (sponge iron and others), especially good - in metallic palladium (about 850 volumes of hydrogen in 1 volume of metal). The heat of combustion of hydrogen is 143.06 MJ/kg.
Exists in the form of diatomic H 2 molecules. The dissociation constant of H2 into atoms at 300 K is 2.56 10–34. The dissociation energy of the H 2 molecule into atoms is 436 kJ/mol. The internuclear distance in the H 2 molecule is 0.07414 nm.
Since the nucleus of each H atom that is part of the molecule has its own spin, molecular hydrogen can be in two forms: in the form of orthohydrogen (o-H 2) (both spins have the same orientation) and in the form of parahydrogen (p-H 2 ) (backs have different orientations). Under normal conditions, normal hydrogen is a mixture of 75% o-H 2 and 25% p-H 2 . The physical properties of p- and o-H 2 differ slightly from each other. So, if the boiling point of pure o-H 2 is 20.45 K, then pure p-n 2 - 20.26 K. Turning o-n 2 in p-H 2 is accompanied by the release of 1418 J/mol of heat.
The high strength of the chemical bond between atoms in the H 2 molecule (which, for example, using the molecular orbital method, can be explained by the fact that in this molecule the electron pair is in the bonding orbital, and the loosening orbital is not populated with electrons) leads to the fact that at room temperature gaseous hydrogen is chemically inactive. So, without heating, with simple mixing, hydrogen reacts (with an explosion) only with gaseous fluorine (F):
H 2 + F 2 \u003d 2HF + Q.
If a mixture of hydrogen and chlorine (Cl) at room temperature is irradiated with ultraviolet light, then an immediate formation of hydrogen chloride HCl is observed. The reaction of hydrogen with oxygen (O) occurs with an explosion if a catalyst is added to the mixture of these gases - metallic palladium (Pd) (or platinum (Pt)). When ignited, a mixture of hydrogen and oxygen (O) (so-called explosive gas) explodes, and an explosion can occur in mixtures in which the hydrogen content is from 5 to 95 volume percent. Pure hydrogen in air or in pure oxygen (O) burns quietly with the release of a large amount of heat:
H 2 + 1 / 2O 2 \u003d H 2 O + 285.75 kJ / mol
If hydrogen interacts with other non-metals and metals, then only under certain conditions (heating, high pressure, the presence of a catalyst). So, hydrogen reacts reversibly with nitrogen (N) at elevated pressure (20-30 MPa and more) and at a temperature of 300-400 ° C in the presence of a catalyst - iron (Fe):
3H 2 + N 2 = 2NH 3 + Q.
Also, only when heated, hydrogen reacts with sulfur (S) to form hydrogen sulfide H 2 S, with bromine (Br) - to form hydrogen bromide HBr, with iodine (I) - to form hydrogen iodide HI. Hydrogen reacts with coal (graphite) to form a mixture of hydrocarbons of various compositions. Hydrogen does not interact directly with boron (B), silicon (Si), phosphorus (P), compounds of these elements with hydrogen are obtained indirectly.
When heated, hydrogen is able to react with alkali, alkaline earth metals and magnesium (Mg) to form compounds with an ionic bond, which contain hydrogen in the oxidation state –1. So, when calcium is heated in a hydrogen atmosphere, a salt-like hydride of the composition CaH 2 is formed. Polymeric aluminum hydride (AlH 3) x - one of the strongest reducing agents - is obtained indirectly (for example, using organoaluminum compounds). With many transition metals (for example, zirconium (Zr), hafnium (Hf), etc.), hydrogen forms compounds of variable composition (solid solutions).
Hydrogen is able to react not only with many simple, but also with complex substances. First of all, it should be noted the ability of hydrogen to reduce many metals from their oxides (such as iron (Fe), nickel (Ni), lead (Pb), tungsten (W), copper (Cu), etc.). So, when heated to a temperature of 400-450 ° C and above, iron (Fe) is reduced by hydrogen from any of its oxides, for example:
Fe 2 O 3 + 3H 2 \u003d 2Fe + 3H 2 O.
It should be noted that only metals located in the series of standard potentials behind manganese (Mn) can be reduced from oxides by hydrogen. More active metals (including manganese (Mn)) are not reduced to metal from oxides.
Hydrogen is capable of adding to a double or triple bond to many organic compounds (these are the so-called hydrogenation reactions). For example, in the presence of a nickel catalyst, hydrogenation of ethylene C 2 H 4 can be carried out, and ethane C 2 H 6 is formed:
C 2 H 4 + H 2 \u003d C 2 H 6.
The interaction of carbon monoxide (II) and hydrogen in industry produces methanol:
2H 2 + CO \u003d CH 3 OH.
In compounds in which a hydrogen atom is connected to an atom of a more electronegative element E (E \u003d F, Cl, O, N), hydrogen bonds form between the molecules (two E atoms of the same or two different elements are interconnected through the H atom: E "... N ... E"", with all three atoms located on the same straight line). Such bonds exist between the molecules of water, ammonia, methanol, etc. and lead to a noticeable increase in the boiling points of these substances, an increase in the heat of evaporation and etc.
Receipt: Hydrogen can be obtained in many ways. In industry, natural gases are used for this, as well as gases obtained from oil refining, coking and gasification of coal and other fuels. In the production of hydrogen from natural gas (the main component is methane), its catalytic interaction with water vapor and incomplete oxidation with oxygen (O) are carried out:
CH 4 + H 2 O \u003d CO + 3H 2 and CH 4 + 1/2 O 2 \u003d CO 2 + 2H 2
The separation of hydrogen from coke gas and refinery gases is based on their liquefaction during deep cooling and removal from the mixture of gases that are more easily liquefied than hydrogen. In the presence of cheap electricity, hydrogen is obtained by electrolysis of water, passing current through alkali solutions. Under laboratory conditions, hydrogen is easily obtained by the interaction of metals with acids, for example, zinc (Zn) with hydrochloric acid.
Application: hydrogen is used in the synthesis of ammonia NH3, hydrogen chloride HCl, methanol CH 3 OH, in the hydrocracking (cracking in a hydrogen atmosphere) of natural hydrocarbons, as a reducing agent in the production of certain metals. By hydrogenation of natural vegetable oils, hard fat is obtained - margarine. Liquid hydrogen finds use as a rocket fuel and also as a coolant. A mixture of oxygen (O) and hydrogen is used in welding.
At one time, it was suggested that in the near future the main source of energy production would be the reaction of hydrogen combustion, and hydrogen energy would replace traditional sources of energy production (coal, oil, etc.). At the same time, it was assumed that for the production of hydrogen on a large scale it would be possible to use the electrolysis of water. Water electrolysis is a rather energy-intensive process, and it is currently unprofitable to obtain hydrogen by electrolysis on an industrial scale. But it was expected that electrolysis would be based on the use of medium temperature (500-600°C) heat, which occurs in large quantities during the operation of nuclear power plants. This heat is of limited use, and the possibility of obtaining hydrogen with its help would solve both the problem of ecology (when hydrogen is burned in air, the amount of environmentally generated harmful substances minimum) and the problem of utilization of medium-temperature heat. However, after the Chernobyl disaster, the development of nuclear energy is curtailed everywhere, so that the indicated source of energy becomes inaccessible. Therefore, the prospects for the widespread use of hydrogen as an energy source are still shifting, at least until the middle of the 21st century.
Features of circulation : hydrogen is not poisonous, but when handling it, one must constantly take into account its high fire and explosion hazard, and the explosion hazard of hydrogen is increased due to the high ability of the gas to diffuse even through some solid materials. Before starting any heating operations in an atmosphere of hydrogen, you should make sure that it is clean (when igniting hydrogen in a test tube turned upside down, the sound should be dull, not barking).
27 The position of microorganisms in the system of the living world. Diversity of microorganisms and their commonality with other organisms. The essential features of microorganisms are: small cell size, high metabolic activity, high plasticity of their metabolism (rapid adaptation to changing environmental conditions, "ubiquity"), the ability to reproduce rapidly, poor morphological differentiation, and a variety of metabolic processes.
Microorganisms, (microbes) - the collective name for a group of living organisms that are too small to be visible to the naked eye (their characteristic size is less than 0.1 mm). Microorganisms include both non-nuclear (prokaryotes: bacteria, archaea) and eukaryotes: some fungi, protists, but not viruses, which are usually isolated into a separate group. Most micro-organisms are single-celled, but there are also multicellular micro-organisms, just as there are some single-celled macro-organisms visible to the naked eye, such as Thiomargarita namibiensis, members of the genus Caulerpa (they are giant polykaryons). Microbiology is the study of these organisms.
The ubiquity and total power of the metabolic potential of microorganisms determines their most important role in the circulation of substances and maintaining dynamic balance in the Earth's biosphere.
A brief review of various representatives of the microcosm, occupying certain "floors" of size, shows that, as a rule, the size of objects is definitely related to their structural complexity. The lower size limit for a free-living single-celled organism is determined by the space required to pack inside the cell the apparatus necessary for independent existence. The limitation of the upper limit of the size of microorganisms is determined, according to modern concepts, by the relationship between the cell surface and volume. With an increase in cellular dimensions, the surface increases in the square, and the volume in the cube, so the ratio between these values shifts towards the latter.
Microorganisms live almost everywhere where there is water, including hot springs, the bottom of the world's oceans, and also deep inside the earth's crust. They are an important link in the metabolism in ecosystems, mainly acting as decomposers, but in some ecosystems they are the only producers of biomass.
Microorganisms living in various environments participate in the cycle of sulfur, iron, phosphorus and other elements, decompose organic substances of animal, vegetable origin, as well as abiogenic origin (methane, paraffins), provide self-purification of water in reservoirs.
However, not all types of microorganisms are beneficial to humans. A very large number of species of microorganisms is opportunistic or pathogenic for humans and animals. Some microorganisms cause damage to agricultural products, deplete the soil with nitrogen, cause pollution of water bodies, and the accumulation of toxic substances in food (for example, microbial toxins).
Microorganisms are characterized by good adaptability to the action of environmental factors. Various microorganisms can grow at temperatures from −6° to +50-75°. The record for survival at elevated temperature was set by archaea, some of the studied cultures of which grow on nutrient media above 110 ° C, for example, Methanopyrus kandleri (strain 116) grows at 122 ° C, a record high temperature for all known organisms.
In nature, habitats with this temperature exist under pressure in hot volcanic springs at the bottom of the oceans (Black smokers).
Microorganisms are known that thrive at levels of ionizing radiation that are fatal for multicellular creatures, in a wide range of pH values, at 25% sodium chloride concentration, in conditions of various oxygen contents up to its complete absence (Anaerobic microorganisms).
At the same time, pathogenic microorganisms cause diseases in humans, animals and plants.
The most widely accepted theories about the origin of life on Earth suggest that protomicroorganisms were the first living organisms to emerge through evolution.
Currently, all microorganisms are divided into 3 kingdoms:
1. Procariota. All types of bacteria, rickettsia, chlamydia, mycoplasmas, etc. can be attributed to this kingdom. Cells have a nucleus with one chromosome. The nucleus is not separated from the cytoplasm of the cell. A simple dividing cycle by constriction. There are a number of unique organelles such as plasmids, mesosomes. There is no ability for photosynthesis.
2. Eucariotae. Representatives of this kingdom are fungi and protozoa. The cell contains a nucleus, delimited from the cytoplasm by a membrane, with several chromosomes. There are a number of organelles characteristic of higher animals: mitochondria, endoplasmic reticulum, Golgi apparatus. Some representatives of this kingdom have chloroplasts and are capable of photosynthesis. They have a complex life cycle.
3. Vira. Viruses belong to this kingdom. The hallmark of a virion is the presence of only one type of nucleic acid: RNA or DNA enclosed in a capsid. A virus may not have a common outer shell. The reproduction of the virus can occur only after embedding in another cell, where replication takes place.
Nitrous acid exists either in solution or in the gas phase. It is unstable and decomposes in vapors when heated:
2HNO 2 "NO + NO 2 + H 2 O
Aqueous solutions of this acid decompose when heated:
3HNO 2 "HNO 3 + H 2 O + 2NO
This reaction is reversible, therefore, although the dissolution of NO 2 is accompanied by the formation of two acids: 2NO 2 + H 2 O \u003d HNO 2 + HNO 3
practically by the interaction of NO 2 with water, HNO 3 is obtained:
3NO 2 + H 2 O \u003d 2HNO 3 + NO
In terms of acidic properties, nitrous acid is only slightly stronger than acetic acid. Its salts are called nitrites and, unlike the acid itself, are stable. From solutions of its salts, by adding sulfuric acid, a solution of HNO 2 can be obtained:
Ba(NO 2) 2 + H 2 SO 4 \u003d 2HNO 2 + BaSO 4 ¯
Based on data on its compounds, two types of structure of nitrous acid are suggested:
which correspond to nitrites and nitro compounds. Nitrites of active metals have a type I structure, and low-active metals - type II. Almost all salts of this acid are highly soluble, but silver nitrite is the most difficult of all. All salts of nitrous acid are poisonous. For chemical technology, KNO 2 and NaNO 2 are important, which are necessary for the production of organic dyes. Both salts are obtained from nitrogen oxides:
NO + NO 2 + NaOH \u003d 2NaNO 2 + H 2 O or when their nitrates are heated:
KNO 3 + Pb \u003d KNO 2 + PbO
Pb is needed to bind the released oxygen.
Of the chemical properties of HNO 2, oxidative ones are more pronounced, while it itself is reduced to NO:
However, many examples of such reactions can be given, where nitrous acid exhibits reducing properties:
The presence of nitrous acid and its salts in a solution can be determined by adding a solution of potassium iodide and starch. The nitrite ion oxidizes the iodine anion. This reaction requires the presence of H + , i.e. runs in an acidic environment.
Nitric acid
Under laboratory conditions, nitric acid can be obtained by the action of concentrated sulfuric acid on nitrates:
NaNO 3 + H 2 SO 4 (c) \u003d NaHSO 4 + HNO 3 The reaction proceeds with slight heating.
Obtaining nitric acid on an industrial scale is carried out by catalytic oxidation of ammonia with atmospheric oxygen:
1. First, a mixture of ammonia and air is passed over a platinum catalyst at 800°C. Ammonia is oxidized to nitric oxide (II):
4NH 3 + 5O 2 \u003d 4NO + 6H 2 O
2. Upon cooling, NO is further oxidized to NO 2: 2NO + O 2 \u003d 2NO 2
3. The resulting nitric oxide (IV) dissolves in water in the presence of excess O 2 to form HNO 3: 4NO 2 + 2H 2 O + O 2 \u003d 4HNO 3
The starting products - ammonia and air - are thoroughly cleaned of harmful impurities that poison the catalyst (hydrogen sulfide, dust, oils, etc.).
The resulting acid is dilute (40-60%). Concentrated nitric acid (96-98%) is obtained by distillation of dilute acid mixed with concentrated sulfuric acid. In this case, only nitric acid evaporates.
Physical properties
Nitric acid is a colorless liquid with a pungent odor. Very hygroscopic, "smoke" in the air, because. its vapors with air moisture form fog drops. Miscible with water in any ratio. At -41.6°C it passes into a crystalline state. Boils at 82.6°C.
In HNO 3, the nitrogen valence is 4, the oxidation state is +5. The structural formula of nitric acid is depicted as follows:
Both oxygen atoms, bound only to nitrogen, are equivalent: they are at the same distance from the nitrogen atom and each carry a half electron charge, i.e. a quarter of the nitrogen is divided equally between the two oxygen atoms.
The electronic structure of nitric acid can be derived as follows:
1. A hydrogen atom is bound to an oxygen atom by a covalent bond:
2. Due to the unpaired electron, the oxygen atom forms a covalent bond with the nitrogen atom:
3. Two unpaired electron nitrogen atom form a covalent bond with the second oxygen atom:
4. The third oxygen atom, being excited, forms a free 2p- orbital by electron pairing. The interaction of a lone pair of nitrogen with a free orbital of the third oxygen atom leads to the formation of a nitric acid molecule:
Chemical properties
1. Diluted nitric acid exhibits all the properties of acids. It belongs to strong acids. Dissociates in aqueous solutions:
HNO 3 "H + + NO - 3 Under the influence of heat and in the light, it partially decomposes:
4HNO 3 \u003d 4NO 2 + 2H 2 O + O 2 Therefore, store it in a cool and dark place.
2. Nitric acid is characterized by exclusively oxidizing properties. The most important chemical property is the interaction with almost all metals. Hydrogen is never released. The recovery of nitric acid depends on its concentration and the nature of the reducing agent. The degree of nitrogen oxidation in the reduction products is in the range from +4 to -3:
HN +5 O 3 ®N +4 O 2 ®HN +3 O 2 ®N +2 O®N +1 2 O®N 0 2 ®N -3 H 4 NO 3
The reduction products in the interaction of nitric acid of different concentrations with metals of different activity are shown below in the scheme.
Concentrated nitric acid at normal temperature does not interact with aluminum, chromium, iron. She puts them in a passive state. A film of oxides forms on the surface, which is impermeable to concentrated acid.
3. Nitric acid does not react with Pt, Rh, Ir, Ta, Au. Platinum and gold are dissolved in "aqua regia" - a mixture of 3 volumes of concentrated hydrochloric acid and 1 volume of concentrated nitric acid:
Au + HNO 3 + 3HCl \u003d AuCl 3 + NO + 2H 2 O HCl + AuCl 3 \u003d H
3Pt + 4HNO 3 + 12HCl \u003d 3PtCl 4 + 4NO + 8H 2 O 2HCl + PtCl 4 \u003d H 2
The action of "royal vodka" is that nitric acid oxidizes hydrochloric acid to free chlorine:
HNO 3 + HCl \u003d Cl 2 + 2H 2 O + NOCl 2NOCl \u003d 2NO + Cl 2 The released chlorine combines with metals.
4. Non-metals are oxidized by nitric acid to the corresponding acids, and depending on the concentration, it is reduced to NO or NO 2:
S + bHNO 3 (conc) \u003d H 2 SO 4 + 6NO 2 + 2H 2 OR + 5HNO 3 (conc) \u003d H 3 PO 4 + 5NO 2 + H 2 O I 2 + 10HNO 3 (conc) \u003d 2HIO 3 + 10NO 2 + 4H 2 O 3P + 5HNO 3 (p azb) + 2H 2 O \u003d 3H 3 RO 4 + 5NO
5. It also interacts with organic compounds.
Salts of nitric acid are called nitrates, they are crystalline substances that are highly soluble in water. They are obtained by the action of HNO 3 on metals, their oxides and hydroxides. Potassium, sodium, ammonium and calcium nitrates are called saltpeters. Saltpeter is used mainly as a mineral nitrogen fertilizer. In addition, KNO 3 is used to prepare black powder (a mixture of 75% KNO 3 , 15% C and 10% S). Ammonal explosive is made from NH 4 NO 3, aluminum powder and trinitrotoluene.
Salts of nitric acid decompose when heated, and the decomposition products depend on the position of the salt-forming metal in a series of standard electrode potentials:
Decomposition on heating (thermolysis) - important property salts of nitric acid.
2KNO 3 \u003d 2KNO 2 +O 2
2Cu(NO 3) 2 \u003d 2CuO + NO 2 + O 2
Metal salts located in the row to the left of Mg form nitrites and oxygen, from Mg to Cu - metal oxide, NO 2 and oxygen, after Cu - free metal, NO 2 and oxygen.
Application
Nitric acid is the most important product of the chemical industry. Large quantities are spent on the preparation of nitrogen fertilizers, explosives, dyes, plastics, artificial fibers, and other materials. fuming
nitric acid is used in rocket technology as an oxidizing agent for rocket fuel.
Nitrous acid HN0 2 is known only in dilute solutions. It is unstable, so it does not exist in its pure form. The formula of nitrous acid can be represented as two tautomeric forms:
Nitrite ion N0 2 has an angular shape:
When heated, nitrous acid breaks down:
Nitrogen in nitrous acid has an oxidation state of +3, which corresponds to an intermediate state between the highest (+5) and lowest (-3) oxidation states. Therefore, nitrous acid exhibits both oxidizing and reducing properties.
Oxidizing agent:
Reducing agent:
Salts of nitrous acid - nitrites - are stable compounds and, with the exception of AgNO 2, are easily soluble in water. Like nitrous acid itself, nitrites have redox properties.
Oxidizing agent:
Reducing agent:
The reaction with KI in an acidic medium is widely used in analytical chemistry to detect the nitrite ion NO 2 (free iodine liberated colors the starch solution).
Most salts of nitrous acid are poisonous. The greatest application is sodium nitrite NaN0 2, which is widely used in the production of organic dyes, drugs, and in analytical chemistry. V medical practice used as a vasodilator for angina pectoris.
Nitric acid HN0 3 in laboratory conditions can be obtained by the action of concentrated sulfuric acid on NaN0 3:
Nitric acid is commercially produced by the catalytic oxidation of ammonia with atmospheric oxygen. This method of obtaining HN() 3 consists of several stages. First, a mixture of ammonia with air is passed over a platinum catalyst at 800°C. Ammonia is oxidized to NO:
Upon cooling, NO is further oxidized to NO 2:
The resulting NO 2 dissolves in water to form HN0 3:
Pure nitric acid is a colorless liquid which becomes crystalline at 42°C. In the air, it "smokes", since its vapors with air moisture form small droplets of fog. It is miscible with water in any ratio. HN0 3 has a flat structure:
The nitrogen in HN0 3 is singly charged and tetracovalent. The nitrate ion N0 3 has the shape of a flat triangle, which is explained by the ^-hybridization of the valence orbitals of nitrogen:
Nitric acid is one of the strongest acids. In aqueous solutions, it is completely dissociated into H + and N0 3 ions.
Nitric acid is characterized exclusively by oxidizing properties. The nitrogen in nitric acid is in the highest oxidation state of +5, so it can only gain electrons. Already under the influence of light, nitric acid decomposes with the release of NO 2 and 0 2:
Depending on the concentration of nitric acid and the nature of the reducing agent, various products are formed, where nitrogen exhibits an oxidation state from +4 to
Concentrated nitric acid oxidizes most metals (except gold and platinum).
When concentrated HN0 3 interacts with low-active metals, as a rule, NO 2 is formed:
However, dilute nitric acid in this case is reduced to NO:
If more active metals enter into the oxidation reaction with dilute nitric acid, then N 3 0 is released:
Very dilute nitric acid, when interacting with active metals, is reduced to ammonium salts:
Iron readily reacts with dilute nitric acid and does not react with concentrated nitric acid in the cold. Chrome and aluminum behave similarly. This is explained by the fact that oxide films are formed on the surface of these metals, which inhibit further oxidation of the metal (metal passivation).
Thus, when nitric acid interacts with metals, hydrogen is not released.
Non-metals, when heated with HN0 3, are oxidized to oxygen acids. Depending on the concentration, nitric acid is reduced to NO 2 or NO:
A mixture of one volume of nitric acid and three volumes of concentrated hydrochloric acid is called royal vodka. This mixture is a stronger oxidizing agent and dissolves noble metals such as gold and platinum. The action of aqua regia is based on the fact that HNO 3 oxidizes HC1 with the release of nitrosyl chloride, which decomposes with the formation of atomic chlorine and NO. Chlorine plays the role of an oxidizing agent when interacting with metals:
Interaction with gold proceeds according to the reaction
Nitric acid, depending on the concentration, behaves differently with respect to sulfides, which exhibit reducing properties. So, dilute nitric acid (up to 20%) oxidizes the sulfide ion S 2- to neutral sulfur, and itself is reduced to NO. A more concentrated nitric acid (30% solution) oxidizes S 2 to SOf, while being reduced to NO:
In anhydrous nitric acid, the following equilibrium processes take place:
To recognize the nitrate ion N0 3 and distinguish it from the nitrite ion N0 2, several reactions are used:
a) nitrates in an alkaline environment can be reduced to ammonia with metals - zinc or aluminum:
- (gaseous ammonia released can be detected by the blue color of wet litmus paper);
- b) iron sulfate (I) in an acidic environment is oxidized by nitric acid to iron sulfate (III). Nitric acid is reduced to NO, which with an excess of FeSO^ forms a brown complex compound:
Salts of nitric acid, called nitrates, are crystalline substances that are highly soluble in water. When heated, they decompose with the release of 0 9 . Nitrates containing alkali metals and metals standing in a series of standard electrode potentials to the left of magnesium (including magnesium), with the elimination of oxygen, pass into the corresponding nitrites:
Nitrates of metals that are in the series of standard electrode potentials to the right of copper are split with the formation of free metals:
Nitrates of other metals decompose to oxides:
For qualitative detection, the reaction is used
as a result of which brown gas (NO 9) is released.
Since nitrates easily split off oxygen at high temperatures and, therefore, are oxidizing agents, they are used to make flammable and explosive mixtures. For example, gunpowder is a mixture of 68% KN0 3 , 15% S and 17% C.
The most important are NaNO ;j (Chilean nitrate), KN0 3 (potassium nitrate), NH 4 N0 3 (ammonium nitrate) and Ca (NO: i) 2 (calcium nitrate). All of these compounds are used in agriculture as a fertilizer.
Biological role nitrogen. Nitrogen is a macroelement that is part of the amino acids of proteins, RNA and DNA, hormones, enzymes, vitamins and many other vital substrates.
Nitrous acid
HNO 2 is a weak monobasic acid that exists only in dilute aqueous solutions.
Salts of nitrous acid are called nitrites. Nitrites are much more stable than HNO 2 and are all toxic.
Receipt:
1. N 2 O 3 + H 2 O \u003d 2HNO 2
How else can you get nitrous acid? ()
What is the oxidation state in nitrous acid?
This means that the acid exhibits both oxidizing and reducing properties.
Under the action of stronger oxidizing agents, it is oxidized to HNO 3:
5HNO 2 + 2HMnO 4 → 2Mn(NO 3) 2 + HNO 3 + 3H 2 O;
HNO 2 + Cl 2 + H 2 O → HNO 3 + 2HCl.
2HNO 2 + 2HI → 2NO + I 2 ↓ + 2H 2 O - reducing properties
Qualitative reaction to nitrite ion NO 2 – – interaction of nitrites with a solution of potassium iodide KI acidified with dilute sulfuric acid.
How should starch iodine paper change color under the action of free I 2?
Getting salts (nitrates and nitrites)
What are the methods of obtaining salts that you know? How can you get nitrates and nitrites?
1) Metal + non-metal = salt;
2) metal + acid = salt + hydrogen;
3) metal oxide + acid = salt + water;
4) metal hydroxide + acid = salt + water;
5) metal hydroxide + acid oxide = salt + water;
6) metal oxide + non-metal oxide = salt;
7) salt 1 + metal hydroxide (alkali) = salt 2 + metal hydroxide (insoluble base);
8) salt 1 + acid (strong) = salt 2 + acid (weak);
9) salt 1 + salt 2 = salt 3 + salt 4
10) salt 1 + metal (active) = salt 2 + metal (less active).
A specific way to obtain nitrates and nitrites:
disproportionation.
In the presence of excess oxygen
Salts of nitric acid - nitrates
nitrates of alkali metals, calcium, ammonium - saltpeter
KNO 3 - potassium nitrate,
NH 4 NO 3 - ammonium nitrate.
Physical properties:
All nitrates are crystalline solids white color, highly soluble in water. Poisonous!
Chemical properties of nitrates
Interaction of nitrates with metals, acids, alkalis, salts
Exercise. Mark the signs of each reaction, write down the molecular and ionic equations corresponding to the schemes:
Cu(NO 3) 2 + Zn…,
AgNO 3 + HCl ...,
Cu(NO 3) 2 + NaOH…,
AgNO 3 + BaCl 2 ....
Decomposition of nitrates
When solid nitrates are heated, they all decompose with the release of oxygen (the exception is ammonium nitrate), while they can be divided into three groups.
The first group consists of alkali metal nitrates
2KNO 3 \u003d 2KNO 2 + O 2.
The second group from alkaline earth metals to copper inclusive
2Cu (NO 3) 2 \u003d 2CuO + 4NO 2 + O 2,
The third Me group after Cu
Hg (NO 3) 2 \u003d Hg + 2NO 2 + O 2,
Why is there a lot of nitrogen in nature (it is part of the atmosphere), and plants often give a poor harvest due to nitrogen starvation? (Plants cannot absorb molecular nitrogen from the air. With a lack of nitrogen, the formation of chlorophyll is delayed, the growth and development of the plant is delayed.)
Name the ways of assimilation of atmospheric nitrogen.
(Part of the bound nitrogen enters the soil during thunderstorms. Legumes, on the roots of which nodule bacteria develop that can bind atmospheric nitrogen, converting it into compounds available to plants.)
When harvesting, a person annually carries away with them huge amounts of bound nitrogen. He covers this loss by introducing not only organic, but also mineral fertilizers (nitrate, ammonia, ammonium). Nitrogen fertilizers are applied to all crops. Nitrogen is absorbed by plants in the form of ammonium cation and nitrate anion NO 3 - .
Student reports
Effect of nitrates on environment and the human body
First aid for nitrate poisoning
Reasons for the accumulation of nitrates in vegetables and methods for growing environmentally friendly crop products
