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 the moisture of 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 the acid, the faster the decomposition proceeds. 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 Н + 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 oxidants. Many non-metals are easily oxidized by it, turning into the corresponding acids. So, when boiling with nitric acid, sulfur is gradually oxidized into sulfuric acid, phosphorus - into phosphoric. 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), converting them into nitrates, and some metals into oxides.

Concentrated HNO 3 passivates some metals. Lomonosov discovered that iron, which easily dissolves 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 into a passive state.

The oxidation state of nitrogen in nitric acid is 4-5. Acting as an oxidizing agent, HNO 3 can be reduced to various products:

Receiving.

1. In the laboratory, nitric acid is obtained by the interaction of 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 takes place 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 example:

4HNO 3 + Ni → Ni (NO 3) 2 + 2NO 2 + 2H 2 O.

6. Similarly concentrated HNO 3 reacts with non-metals. In this case, the non-metal is oxidized. For example:

5HNO 3 + Po → HP + 5O 3 + 5NO 2 + 2H 2 O.

C oles of nitric acid - 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 of Сu MeNO 3 → Me + NO 2 + O 2

Application.

Nitric acid is used to obtain nitrogen fertilizers, medicinal and explosives.

Hydrogen. Atomic structure, physical and chemical properties, 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, natural hydrogen always contains trace amounts of a radioactive nuclide - tritium 3 H (half-life T1 / 2 = 12.43 years). Since the nucleus of the hydrogen atom contains only 1 proton (there can be no less protons in the nucleus of the element), it is sometimes said that hydrogen forms the natural lower boundary of the periodic table of elements of D.I.Mendeleev (although the element hydrogen itself is located in the very upper part tables). The element hydrogen is located in the first period of the periodic table. It also belongs to the 1st group (group IA alkali metals), and to the 7th group (group VIIA of halogens).

The atomic masses of hydrogen isotopes differ very strongly (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 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 (Latin Protium, from the Greek protos - the first), denoted by the symbol H, and its nucleus is called a proton, the symbol p. Hydrogen with a mass number of 2 is called heavy hydrogen, deuterium (Latin Deuterium, from the Greek deuteros - the second), for its designation use the symbols 2 H, or D (read "de"), the nucleus d - deuteron. A radioactive isotope with a mass number of 3 is called superheavy hydrogen, or tritium (Latin Tritum, from the Greek tritos - the third), the symbol 3 H or T (read "te"), the t nucleus is triton.

The configuration of the only electron layer of a neutral unexcited hydrogen atom is 1s1. In compounds, it exhibits oxidation states +1 and, less often, –1 (valence 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: under 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 boiling point) has a density of 70.8 kg / m 3 and is the lightest liquid. The standard electrode potential Н 2 / Н– 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 (spongy 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.

It exists in the form of diatomic H2 molecules. The dissociation constant of H2 into atoms at 300 K is 2.56 · 10–34. The dissociation energy of the Н 2 molecule into atoms is 436 kJ / mol. The internuclear distance in the H2 molecule is 0.07414 nm.

Since the nucleus of each H atom included in 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 ) (the backs have a different orientation). Under normal conditions, normal hydrogen is a mixture of 75% o-H 2 and 25% p-H2. Physical properties n- 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. O-H transformation 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 H2 molecule (which, for example, using the method of molecular orbitals, can be explained by the fact that in this molecule the electron pair is in the bonding orbital, and the antibonding orbital is not populated by electrons) leads to the fact that at room temperature gaseous hydrogen is chemically inactive. So, without heating, with simple mixing, hydrogen reacts (explosively) only with gaseous fluorine (F):

H 2 + F 2 = 2HF + Q.

If a mixture of hydrogen and chlorine (Cl) is irradiated with ultraviolet light at room temperature, the immediate formation of hydrogen chloride HCl is observed. The reaction of hydrogen with oxygen (O) occurs explosively if a catalyst - metallic palladium (Pd) (or platinum (Pt)) - is added to the mixture of these gases. When ignited, a mixture of hydrogen and oxygen (O) (the so-called detonating gas) explodes, and an explosion can occur in mixtures in which the hydrogen content is from 5 to 95 percent by volume. 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 = H 2 O + 285.75 kJ / mol

If hydrogen interacts with other non-metals and metals, then only under certain conditions (heating, high pressure, presence of a catalyst). Thus, 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) with the formation of hydrogen sulfide H 2 S, with bromine (Br) - with the formation of hydrogen bromide HBr, with iodine (I) - with the formation of hydrogen iodide HI. Hydrogen reacts with coal (graphite) to form a mixture of hydrocarbons of various compositions. Hydrogen does not directly interact with boron (B), silicon (Si), phosphorus (P), compounds of these elements with hydrogen are obtained indirectly.

When heated, hydrogen is capable of reacting 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. Polymer aluminum hydride (AlH 3) x - one of the most powerful 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 capable of reacting 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 higher, iron (Fe) is reduced by hydrogen from any of its oxide, for example:

Fe 2 O 3 + 3H 2 = 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 with hydrogen. More active metals (including manganese (Mn)) are not reduced to metal from oxides.

Hydrogen is able to bind via 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 = C 2 H 6.

Methanol is obtained by the interaction of carbon monoxide (II) and hydrogen in industry:

2H 2 + CO = CH 3 OH.

In compounds in which a hydrogen atom is connected to an atom of a more electronegative element E (E = F, Cl, O, N), hydrogen bonds are formed between the molecules (two E atoms of the same or two different elements are linked through the H atom: E "... N ... E" ", and all three atoms are located on one 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 vaporization and etc.

Receiving: hydrogen can be obtained in many ways. In industry, natural gases are used for this, as well as gases obtained during 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 = CO + 3H 2 and CH 4 + 1/2 O 2 = CO 2 + 2H 2

The release of hydrogen from coke oven gas and refinery gases is based on their liquefaction during deep cooling and removal from the mixture of gases liquefied more easily than hydrogen. In the presence of cheap electricity, hydrogen is obtained by electrolysis of water, passing a 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 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, a hard fat - margarine is obtained. Liquid hydrogen is used as a propellant and also as a refrigerant. A mixture of oxygen (O) with hydrogen is used in welding.

At one time, it was suggested that in the near future, the main source of energy production will be the reaction of hydrogen combustion, and hydrogen energy will replace traditional sources of energy production (coal, oil, etc.). It was assumed that water electrolysis could be used to produce hydrogen on a large scale. Water electrolysis is a rather energy-consuming process, and it is currently unprofitable to obtain hydrogen by electrolysis on an industrial scale. But electrolysis was expected to 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 has limited application, and the possibility of obtaining hydrogen with its help would solve both the environmental problem (when hydrogen burns in air, the amount of ecologically harmful substances formed is minimal), and the problem of utilizing medium-temperature heat. However, after the Chernobyl disaster, the development of nuclear energy is being curtailed everywhere, so that this source of energy becomes unavailable. Therefore, the prospects for the widespread use of hydrogen as a source of energy are still shifting, at least until the middle of the 21st century.

Features of treatment : hydrogen is not poisonous, but when handling it, it is necessary to 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 a hydrogen atmosphere, make sure that it is clean (when igniting hydrogen in an upside-down test tube, the sound should be dull, not barking).

27 Position of microorganisms in the system of the living world. Diversity of microorganisms and their commonality with other organisms. Essential features of microorganisms: 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, a variety of metabolic processes.

Microorganisms, (microbes) is a 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). The composition of microorganisms includes both non-nuclear (prokaryotes: bacteria, archaea) and eukaryotes: some fungi, protists, but not viruses, which are usually isolated into a separate group. Most microorganisms consist of one cell, but there are also multicellular microorganisms, just as there are some unicellular microorganisms visible to the naked eye, for example Thiomargarita namibiensis, representatives of the genus Caulerpa (are giant polycarions). The study of these organisms is the science of microbiology.

The ubiquity and total capacity of the metabolic potential of microorganisms determines their most important role in the circulation of substances and the maintenance of dynamic equilibrium in the Earth's biosphere.

A brief examination of various representatives of the microworld, occupying certain "levels" of size, shows that, as a rule, the size of objects is definitely related to their structural complexity. The lower limit of the size of a free-living unicellular organism is determined by the space required for packing the apparatus inside the cell, which is necessary for independent existence. The limitation of the upper limit of the size of microorganisms is determined, according to modern concepts, by the ratio between the cell surface and the volume. With an increase in cell size, the surface increases in a square, and the volume in a cube, therefore, the ratio between these values ​​shifts towards the latter.

Microorganisms are found almost everywhere there is water, including hot springs, the ocean floor, and deep within the earth's crust. They are an important link in the metabolism in ecosystems, mainly playing the role of decomposers, but in some ecosystems they are the only biomass producers - producers.

Microorganisms living in various environments participate in the cycle of sulfur, iron, phosphorus and other elements, decompose organic matter of animal, plant origin, as well as abiogenic origin (methane, paraffins), and provide self-purification of water in reservoirs.

However, not all types of microorganisms are beneficial to humans. A very large number of types of microorganisms are conditionally pathogenic or pathogenic for humans and animals. Some microorganisms cause deterioration of agricultural products, deplete the soil with nitrogen, cause pollution of water bodies, the accumulation of toxic substances (for example, microbial toxins) in food.

Microorganisms are distinguished 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 temperatures 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, a habitat with this temperature exists 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 varying oxygen content up to its complete absence (Anaerobic microorganisms).

At the same time, pathogenic microorganisms cause diseases in humans, animals and plants.

The most generally accepted theories about the origin of life on Earth suggest that proto-microorganisms were the first living organisms to appear in the process of evolution.

Currently, all microorganisms are divided into 3 kingdoms:

1. Procariotae. This kingdom includes all types of bacteria, rickettsia, chlamydia, mycoplasma, etc. Cells have a nucleus with one chromosome. The nucleus is not separated from the cytoplasm of the cell. Simple cycle of division by constriction. There are a number of unique organelles such as plasmids and mesosomes. There is no ability for photosynthesis.

2. Eucariotae. The representatives of this kingdom are mushrooms and protozoa. The cell contains a nucleus, separated from the cytoplasm by a membrane, with several chromasomes. 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. Have a complex life cycle.

3. Vira. Viruses belong to this kingdom. Distinctive features of the virion is the presence of only one type of nucleic acid: RNA or DNA, enclosed in a capsid. The virus may not have a common outer shell. Reproduction of the virus can occur only after incorporation into another cell, where replication takes place.

Nitrous acid

If potassium or sodium nitrate is heated, they lose some of the oxygen and pass into the nitrous acid salt HNO2. Decomposition is easier in the presence of lead, which binds the released oxygen:

Nitrous acid salts - nitrites - form crystals that are readily soluble in water (with the exception of silver nitrite). Sodium nitrite NaNO 2 is used in the production of various dyes.

When a solution of some nitrite is acted upon with dilute sulfuric acid, free nitrous acid is obtained:

It belongs to the group of weak acids (K = A- 10 ~ 4) and is known only in highly dilute aqueous solutions. When the solution is concentrated or when it is heated, nitrous acid decomposes:

The oxidation state of nitrogen in nitrous acid is +3, i.e. is intermediate between the lowest and highest possible values ​​of the nitrogen oxidation state. Therefore, HNO 2 exhibits redox duality. Under the action of reducing agents, it is reduced (usually to NO), and in reactions with oxidants, it is oxidized to HNO 3. Examples include the following reactions:

Nitric acid

Pure nitric acid HNO3 is a colorless liquid with a density of 1.51 g / cm3, which solidifies into a transparent crystalline mass at -42 ° C. In the air, like concentrated hydrochloric acid, it “smokes”, since its vapors form small droplets of fog with moisture in the air.

Nitric acid is not durable. Already under the influence of light, it gradually decomposes:

The higher the temperature and the more concentrated the acid, the faster the decomposition proceeds. 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.

A characteristic property of nitric acid is its pronounced oxidizing ability. Nitric acid is one of the most energetic oxidants. Many non-metals are easily oxidized by it, turning into the corresponding acids. So, when boiling with nitric acid, sulfur is gradually oxidized 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), converting them into nitrates, and some metals into oxides.

Concentrated HNO 3 passivates some metals. Lomonosov discovered that iron, which easily dissolves 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 pass into a passive state under the action of concentrated nitric acid (see § 100).

The oxidation state of nitrogen in nitric acid is +5. Acting as an oxidizing agent, HNO 3 can be reduced to various products:

Which of these substances is formed, i.e. how deeply nitric acid is reduced in a particular case depends on the nature of the reducing agent and on the reaction conditions, primarily on the concentration of the acid. The higher the concentration of HNO 3, the less deeply it is restored. In reactions with concentrated acid, NO 2 is most often released. When dilute nitric acid interacts with low-activity metals, such as copper, NO is released. In the case of more active metals - iron, zinc - N 2 O is formed. Strongly diluted nitric acid interacts with active metals - zinc, magnesium, aluminum - to form an ammonium ion, which gives ammonium nitrate with the acid. Usually several products are formed at the same time.

To illustrate, we present the reaction schemes for the oxidation of some metals with nitric acid:

When nitric acid acts on metals, hydrogen, as a rule, does not evolve.

When non-metals are oxidized, concentrated nitric acid, as in the case of metals, is reduced to NO 2, for example:

More dilute acid is usually reduced to NO, for example:

The given schemes illustrate the most typical cases of interaction of nitric acid with metals and non-metals. In general, redox reactions involving HNO 3 are difficult.

A mixture consisting of 1 volume of nitric acid and 3-4 volumes of concentrated hydrochloric acid is called aqua regia. Tsar's vodka dissolves some metals that do not interact with nitric acid, including the "king of metals" - gold. Its action is explained by the fact that nitric acid oxidizes hydrochloric acid with the release of free chlorine and the formation nitrogen chloroxide(III), or nitrosyl chloride, NOCl:

Nitrosyl chloride is an intermediate reaction product and decomposes:

Chlorine at the time of release consists of atoms, which determines the high oxidizing ability of aqua regia. Oxidation reactions of gold and platinum proceed mainly according to the following equations:

With an excess of hydrochloric acid, gold (III) chloride and platinum (IV) chloride form complex compounds H [AuCl 4] and H 2.

For many organic matter nitric acid acts so that one or more hydrogen atoms in the molecule organic compound are replaced by nitro groups - NO 2. This process is called nitration and has great importance in organic chemistry.

The electronic structure of the HNO 3 molecule is discussed in § 44.

Nitric acid is one of the most important nitrogen compounds: it is consumed in large quantities in the production of nitrogen fertilizers, explosives and organic dyes, serves as an oxidizing agent in many chemical processes, is used in the production of sulfuric acid by the nitrous method, and is used for the manufacture of cellulose varnishes and film.

Nitric acid salts are called nitrates. All of them dissolve well in water, and when heated they decompose with the release of oxygen. In this case, the nitrates of the most active metals pass into nitrites:

When heated, nitrates of most other metals decompose into metal oxide, oxygen and nitrogen dioxide. For example:

Finally, nitrates of the least active metals (for example, silver, gold) decompose when heated to a free metal:

Easily cleaving off oxygen, nitrates are vigorous oxidizing agents at high temperatures. In contrast, their aqueous solutions show almost no oxidizing properties.

The most important are sodium, potassium, ammonium and calcium nitrates, which in practice are called saltpeter.

Sodium nitrate NaNO 3, or sodium nitrate, sometimes also called Chilean saltpeter, is found in large quantities in nature only in Chile.

Potassium nitrate KNO 3, or potassium nitrate, in small quantities also occurs in nature, but, mainly, it is obtained artificially by the interaction of sodium nitrate with potassium chloride.

Both of these salts are used as fertilizers, and potassium nitrate contains two elements that plants need: nitrogen and potassium. Sodium and potassium nitrates are also used in glass making and in the food industry for preserving food.

Calcium nitrate Ca (NO 3) 2, or calcium nitrate, obtained in large quantities by neutralizing nitric acid with lime; it is used as a fertilizer.

Ammonium nitrate NH 4 NO 3.

• The student is encouraged to compose the complete equations of these reactions himself.

HNO 2 Physical properties State solid Molar mass 47.0134 g / mol Density 1.685 (liq) Thermal properties T. float. 42.35 ° C T. kip. 158 ° C Chemical properties pK a 3.4 Water solubility 548 g / 100 ml Classification Reg. CAS number Data are based on standard conditions (25 ° C, 100 kPa) unless otherwise noted.

Nitrous acid HNO 2 is a weak monobasic acid that exists only in dilute aqueous solutions, colored in a weak blue color, and in the gas phase. Salts of nitrous acid are called nitrites or nitrous acid. Nitrites are much more stable than HNO 2, they are all toxic.

Structure

In the gas phase, the planar molecule of nitrous acid exists in two configurations cis- and trance-.

cis isomer	trans isomer

At room temperature, the trans isomer predominates: this structure is more stable. So, for cis-HNO 2 (g) DG ° f = −42.59 kJ / mol, and for trans-HNO 2 (g) DG = −44.65 kJ / mol.

Chemical properties

In aqueous solutions, there is an equilibrium:

$\backslash \; mathsf\; (2HNO\_2\; \backslash \; rightleftarrows\; N\_2O\_3\; +\; H\_2O\; \backslash \; rightleftarrows\; NO\; \backslash \; uparrow\; +\; NO\_2\; \backslash \; uparrow\; +\; H\_2O)$

When the solution is heated, nitrous acid decomposes with the release and formation of nitric acid:

$\backslash \; mathsf\; (3HNO\_2\; \backslash \; rightleftarrows\; HNO\_3\; +\; 2NO\; \backslash \; uparrow\; +\; H\_2O)$

HNO 2 is a weak acid. In aqueous solutions it dissociates (K D = 4.6 · 10 −4), slightly stronger than acetic acid. Easily displaced over strong acids from salts:

$\backslash \; mathsf\; (H\_2SO\_4\; +\; 2NaNO\_2\; \backslash \; rightarrow\; Na\_2SO\_4\; +\; 2HNO\_2)$

Nitrous acid exhibits both oxidizing and reducing properties. Under the action of stronger oxidants (hydrogen peroxide, chlorine, potassium permanganate), it is oxidized to nitric acid:

$\backslash \; mathsf\; (HNO\_2\; +\; H\_2O\_2\; \backslash \; rightarrow\; HNO\_3\; +\; H\_2O)$ $\backslash \; mathsf\; (HNO\_2\; +\; Cl\_2\; +\; H\_2O\; \backslash \; rightarrow\; HNO\_3\; +\; 2HCl)$ $\backslash \; mathsf\; (5HNO\_2\; +\; 2KMnO\_4\; +\; HNO\_3\; \backslash \; rightarrow\; 2Mn\; (NO\_3)\; \_2\; +\; 2KNO\_3\; +\; 3H\_2O)$

At the same time, it is capable of oxidizing substances with reducing properties:

\ mathsf (2HNO_2 + 2HI \ rightarrow 2NO \ uparrow + I_2 + 2H_2O)

Receiving

Nitrous acid can be obtained by dissolving nitric oxide (III) N 2 O 3 in water:

$\backslash \; mathsf\; (N\_2O\_3\; +\; H\_2O\; \backslash \; rightarrow\; 2HNO\_2)$ $\backslash \; mathsf\; (2NO\_2\; +\; H\_2O\; \backslash \; rightarrow\; HNO\_3\; +\; HNO\_2)$

Application

Nitrous acid is used for diazotization of primary aromatic amines and for the formation of diazonium salts. Nitrites are used in organic synthesis in the production of organic dyes.

Physiological action

Nitrous acid is toxic, and has a pronounced mutagenic effect, since it is a deamination agent.

Sources of

• Karapetyants M. Kh., Drakin S. I. General and inorganic chemistry... Moscow: Chemistry 1994

Write a review on the article "Nitrous acid"

Links

• // Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.

This is a stub for an article on inorganic matter. You can help the project by supplementing it.

An excerpt characterizing Nitrous acid

Sonya, as if not believing her ears, looked with all her eyes at Natasha.
- And Bolkonsky? - she said.
- Oh, Sonya, if only you could know how happy I am! - said Natasha. - You don't know what love is ...
- But, Natasha, is it really all over?
Natasha looked at Sonya with large, open eyes, as if she did not understand her question.
- Well, you refuse to Prince Andrey? - said Sonya.
“Oh, you don’t understand anything, don’t talk nonsense, you listen,” Natasha said with instant annoyance.
“No, I can't believe it,” Sonya repeated. - I do not understand. How did you love one person for a whole year and suddenly ... After all, you only saw him three times. Natasha, I don't believe you, you're being naughty. In three days to forget everything and so ...
“Three days,” Natasha said. - I think I have loved him for a hundred years. It seems to me that I have never loved anyone before him. You cannot understand this. Sonia, wait, sit here. - Natasha hugged and kissed her.
- I was told that it happens and you heard it correctly, but now I have only experienced this love. This is not what it used to be. As soon as I saw him, I felt that he was my master, and I was his slave, and that I could not help but love him. Yes, a slave! What he tells me, I will do. You don't understand this. What am I supposed to do? What am I to do, Sonya? - Natasha said with a happy and frightened face.
“But think about what you’re doing,” Sonya said, “I cannot leave it like that. These secret letters ... How could you allow him to do this? She said with horror and disgust, which she could hardly hide.
“I told you,” Natasha answered, “that I have no will, how you don’t understand this: I love him!
“So I won't allow it to happen, I’ll tell you,” Sonya cried out with tears bursting out.
- What are you, for God's sake ... If you tell me, you are my enemy, - Natasha spoke up. - You want my misfortune, you want us to be torn apart ...
Seeing this fear of Natasha, Sonya cried with tears of shame and pity for her friend.
- But what happened between you? She asked. - What did he tell you? Why doesn't he go to the house?
Natasha did not answer her question.
“For God's sake, Sonya, don’t tell anyone, don’t torture me,” Natasha begged. - You remember that you cannot interfere in such matters. I opened for you ...
- But why these secrets! Why doesn't he go to the house? - asked Sonya. - Why is he not looking for your hand directly? After all, Prince Andrew gave you complete freedom, if so; but I don't believe it. Natasha, did you think what secret reasons could be?
Natasha looked at Sonya with surprised eyes. Apparently, for the first time this question presented itself to her and she did not know how to answer it.
- What are the reasons, I do not know. But there are reasons!
Sonya sighed and shook her head in disbelief.
“If there were reasons…” she began. But Natasha, guessing her doubt, interrupted her in fright.
- Sonya, you can't doubt him, you can't, you can't, do you understand? She shouted.
- Does he love you?
- Does she love? Natasha repeated with a smile of regret about her friend's lack of understanding. - You read the letter, did you see it?
- But if he is an ignoble person?
"He! ... an ignoble man?" If you only knew! - Natasha said.

Nitrous acid

HNO 2 is a weak monobasic acid that exists only in dilute aqueous solutions.

Nitrous acid salts are called nitrites. Nitrites are much more stable than HNO 2, they are all toxic.

Receiving:

1.N 2 O 3 + H 2 O = 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 oxidants, 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 potassium iodide solution KI acidified with dilute sulfuric acid.

How should starch iodine paper change color under the influence of free I 2?

Obtaining salts (nitrates and nitrites)

What are the methods of obtaining salts that you know? How can nitrates and nitrites be obtained?

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).

Specific method for obtaining nitrates and nitrites:

disproportionation.

In the presence of excess oxygen

Nitric acid salts - nitrates

nitrates of alkali metals, calcium, ammonium - saltpeter

KNO 3 - potassium nitrate,

NH 4 NO 3 - ammonium nitrate.

Physical properties:

All nitrates are solid crystalline substances, white, 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), and they can be divided into three groups.

The first group is made up of alkali metal nitrates

2KNO 3 = 2KNO 2 + O 2.

Second group from alkaline earth metals up to copper inclusive

2Сu (NO 3) 2 = 2СuО + 4NО 2 + O 2,

The third group Me after Cu

Hg (NO 3) 2 = Нg + 2NО 2 + О 2,

Why is there a lot of nitrogen in nature (it is part of the atmosphere), and plants often give poor yields due to nitrogen starvation? (Plants cannot assimilate molecular nitrogen from the air. With a lack of nitrogen, the formation of chlorophyll is inhibited, the growth and development of the plant is inhibited.)

What are the ways of assimilating atmospheric nitrogen?

(Part of the bound nitrogen enters the soil during thunderstorms. Legumes, on the roots of which nodule bacteria develop, capable of binding atmospheric nitrogen, converting it into compounds available for plants.)

Taking off crops, a person annually carries away with them huge amounts of bound nitrogen. It covers this decrease by introducing not only organic, but also mineral fertilizers (nitrate, ammonia, ammonium). Nitrogen fertilizers are applied to all crops. Nitrogen is assimilated by plants in the form of ammonium cation and nitrate anion NO 3 -.

Pupil reports

The effect of nitrates on environment and the human body

First aid for nitrate poisoning

Reasons for the accumulation of nitrates in vegetables and methods of growing environmentally friendly crop products

Nitric acid (HNO2) can only exist as a solution or gas. The solution has a pleasant blue tint and is stable at zero degrees. The gas phase of nitric acid has been studied much better than. Its molecule has a flat structure. The bond angles formed by the atoms are 102ᵒ and 111ᵒ, respectively. The nitrogen atom is in a state of sp2 hybridization and has a pair of electrons not bound to the molecule itself. Its oxidation state in nitrous acid is +3. The bond length of atoms does not exceed 0.143 nm. This explains the values ​​of the melting and boiling points of this acid, which are 42 and 158 degrees, respectively.

The oxidation state of nitrogen in the compound is not highest or lowest. This means that nitrous acid can exhibit both oxidizing and reducing properties. When its solution is heated, nitric acid (its chemical HNO3), nitrogen dioxide NO, a colorless poisonous gas, and water are formed. Its oxidizing properties are manifested in the reaction with hydroiodic acid (water, iodine and NO are formed).

Reductive reactions nitrous acid are reduced to the production of nitric acid. Upon reaction with hydrogen peroxide, an aqueous solution of nitric acid is formed. Interaction with strong manganese acid leads to the release of aqueous solution manganese nitrate and nitric acid.

Nitrous acid, when it enters the human body, causes mutagenic changes, i.e. various mutations. It becomes the cause of a qualitative or quantitative change in chromosomes.

Nitrous acid salts

Nitrous acid salts are called nitrites. They are more resistant to high temperatures... Some of them are toxic. When reacting with strong acids, they form sulfates of the corresponding metals and nitrous acid, which is displaced by stronger acids. Many are used in the manufacture of certain dyes, as well as in medicine.

Sodium nitrite is used in the food industry (additive E250). It is a hygroscopic white or yellowish powder that oxidizes in air to sodium nitrate. It is able to kill bacteria and prevent oxidation processes. Due to these properties, it is also used in medicine as an antidote for poisoning people or animals with cyanide.