The chemical properties of hydrogen are oxidizing and reducing. Chemical properties of hydrogen
Hydrogen- the first chemical element of the Periodic Table of chemical elements D.I. Mendeleev. The chemical element hydrogen is located in the first group, the main subgroup, the first period of the Periodic System.
Relative atomic mass of hydrogen = 1.
Hydrogen has the simplest structure of an atom, it consists of a single electron, which is located in the nuclear space. The nucleus of a hydrogen atom consists of one proton.
The hydrogen atom, in chemical reactions, can both donate and add an electron, forming two types of ions:
H0 + 1ē → H1− H0 – 1ē → H1+.
Hydrogen is the most abundant element in the universe. It accounts for about 88.6% of all atoms (about 11.3% are helium atoms, the share of all other elements combined is about 0.1%). Thus, hydrogen is the main component of stars and interstellar gas. In interstellar space, this element exists in the form of individual molecules, atoms, and ions and can form molecular clouds that vary significantly in size, density, and temperature.
The mass fraction of hydrogen in the earth's crust is 1%. It is the ninth most common element. The importance of hydrogen in the chemical processes taking place on Earth is almost as great as that of oxygen. Unlike oxygen, which exists on Earth in both bound and free states, practically all hydrogen on Earth is in the form of compounds; only a very small amount of hydrogen in the form of a simple substance is found in the atmosphere (0.00005% by volume for dry air).
Hydrogen is a constituent of almost all organic substances and is present in all living cells.
Physical properties of hydrogen
A simple substance formed by the chemical element hydrogen has a molecular structure. Its composition corresponds to the formula H2. Like a chemical element, a simple substance is also called hydrogen.
Hydrogen It is a colorless gas, odorless and tasteless, practically insoluble in water. At room temperature and normal atmospheric pressure, the solubility is 18.8 ml of gas per 1 liter of water.
Hydrogen- the lightest gas, its density is 0.08987 g / l. For comparison: the density of air is 1.3 g/l.
Hydrogen can dissolve in metals for example, up to 850 volumes of hydrogen can dissolve in one volume of palladium. Due to its extremely small molecular size, hydrogen is capable of diffusing through many materials.
Like other gases, hydrogen condenses at low temperatures into a colorless transparent liquid, this occurs at a temperature of - 252.8°C. When the temperature reaches -259.2°C, hydrogen crystallizes in the form of white crystals, similar to snow.
Unlike oxygen, hydrogen does not exhibit allotropy.
Application of hydrogen
Hydrogen is used in various industries. A lot of hydrogen goes into ammonia production (NH3). From ammonia, nitrogen fertilizers, synthetic fibers and plastics, and medicines are obtained.
In the food industry, hydrogen is used in the production of margarine, which contains hard fats. To get them from liquid fats, hydrogen is passed through them.
When hydrogen burns in oxygen, the flame temperature is about 2500°C. At this temperature, refractory metals can be melted and welded. Thus, hydrogen is used in welding.
A mixture of liquid hydrogen and oxygen is used as rocket fuel.
Currently, a number of countries have begun research on replacing non-renewable energy sources (oil, gas, coal) with hydrogen. When hydrogen is burned in oxygen, an environmentally friendly product is formed - water, and not carbon dioxide, which causes the greenhouse effect.
Scientists suggest that in the middle of the 21st century, mass production of hydrogen-powered cars should begin. Household fuel cells, whose work is also based on the oxidation of hydrogen with oxygen, will find wide application.
At the end of the 19th and beginning of the 20th centuries, at the dawn of the era of aeronautics, balloons, airships and balloons were filled with hydrogen, since it is much lighter than air. However, the era of airships began to rapidly fade into the past after the disaster that happened to the airship Hindenburg. May 6, 1937 airship, filled with hydrogen, caught fire, resulting in the death of dozens of its passengers.
Hydrogen is extremely explosive in certain proportions with oxygen. Failure to comply with safety regulations led to the ignition and explosion of the airship.
- Hydrogen- the first chemical element of the Periodic Table of chemical elements D.I. Mendeleev
- Hydrogen is located in group I, main subgroup, period 1 of the Periodic System
- Hydrogen valency in compounds - I
- Hydrogen Colorless gas, odorless and tasteless, practically insoluble in water
- Hydrogen- the lightest gas
- Liquid and solid hydrogen is produced at low temperatures
- Hydrogen can dissolve in metals
- Hydrogen applications are varied
Hydrogen
HYDROGEN-but; m. A chemical element (H), a light, colorless and odorless gas that combines with oxygen to form water.
◁ Hydrogen, th, th. V connections. V bacteria. V-th bomb(a bomb of enormous destructive power, the explosive effect of which is based on a thermonuclear reaction). Hydrogenous, th, th.
hydrogen(lat. Hydrogenium), a chemical element of group VII of the periodic system. In nature, there are two stable isotopes (protium and deuterium) and one radioactive isotope (tritium). The molecule is diatomic (H 2). Colorless and odorless gas; density 0.0899 g/l, t kip - 252.76°C. It combines with many elements to form water with oxygen. The most common element in space; makes up (in the form of plasma) more than 70% of the mass of the Sun and stars, the main part of the gases of the interstellar medium and nebulae. The hydrogen atom is part of many acids and bases, most organic compounds. They are used in the production of ammonia, hydrochloric acid, for the hydrogenation of fats, etc., in welding and cutting metals. Promising as a fuel (see. Hydrogen energy).
HYDROGENHYDROGEN (lat. Hydrogenium), H, a chemical element with atomic number 1, atomic mass 1.00794. The chemical symbol for hydrogen, H, is read in our country as "ash", as this letter is pronounced in French.
Natural hydrogen consists of a mixture of two stable nuclides (cm. NUCLIDE) with mass numbers 1.007825 (99.985% in the mixture) and 2.0140 (0.015%). In addition, trace amounts of the radioactive nuclide, tritium, are always present in natural hydrogen. (cm. TRITIUM) 3 H (half-life T 1/2 12.43 years). Since the nucleus of the 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 also belongs to the 1st group (group IA of alkali metals (cm. ALKALI METALS)), and to the 7th group (group VIIA of halogens (cm. 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 (cm. PROTON (elementary particle)), symbol r. Hydrogen with a mass number of 2 is called heavy hydrogen, deuterium (cm. DEUTERIUM)(Latin Deuterium, from 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 2 H or T (read "those"), the nucleus t is a triton.
Configuration of a single electron layer of a neutral unexcited hydrogen atom 1 s 1
. In compounds, it exhibits oxidation states +1 and, less often, -1 (valency I). The radius of the neutral hydrogen atom is 0.024 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.
Discovery history
The release of combustible gas during the interaction of acids and metals was observed in the 16th and 17th centuries at the dawn of the formation of chemistry as a science. The famous English physicist and chemist G. Cavendish (cm. Cavendish Henry) in 1766 he investigated this gas and called it "combustible air". When burned, "combustible air" gave water, but Cavendish's adherence to the theory of phlogiston (cm. PHLOGISTON) prevented him from drawing correct conclusions. French chemist A. Lavoisier (cm. Lavoisier Antoine Laurent) together with engineer J. Meunier (cm. MEUNIER Jean-Baptiste Marie Charles), using special gasometers, in 1783 carried out the synthesis of water, and then its analysis, decomposing water vapor with red-hot iron. Thus, he established that "combustible air" is part of the water and can be obtained from it. In 1787, Lavoisier came to the conclusion that "combustible air" is a simple substance, and therefore belongs to the number of chemical elements. He gave it the name hydrogene (from the Greek hydor - water and gennao - give birth) - "giving birth to water." The establishment of the composition of water put an end to the "phlogiston theory". The Russian name "hydrogen" was proposed by the chemist M.F. Solovyov (cm. SOLOVIEV Mikhail Fedorovich) in 1824. At the turn of the 18th and 19th centuries, it was found that the hydrogen atom is very light (compared to the atoms of other elements), and the weight (mass) of the hydrogen atom was taken as a unit for comparing the atomic masses of elements. The mass of the hydrogen atom was assigned a value equal to 1.
Being in nature
Hydrogen accounts for about 1% of the mass of the earth's crust (10th place among all elements). Hydrogen is practically never found in its free form on our planet (its traces are found in the upper atmosphere), but it is distributed almost everywhere on Earth in the composition of water. The element hydrogen is a part of organic and inorganic compounds of living organisms, natural gas, oil, coal. It is contained, of course, in the composition of water (about 11% by weight), in various natural crystalline hydrates and minerals, which contain one or more OH hydroxo groups.
Hydrogen as an element dominates the universe. It accounts for about half the mass of the Sun and other stars, it is present in the atmosphere of a number of planets.
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 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 with hydrochloric acid.
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 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 H 2 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, which is part of the molecule, has its own spin (cm. SPIN), then 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) (spins 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-H 2 is 20.26 K. The transformation of o-H 2 into p-H 2 is accompanied by the release of 1418 J / mol of heat.
Considerations have been repeatedly expressed in the scientific literature that at high pressures (above 10 GPa) and at low temperatures (about 10 K and below), solid hydrogen, which usually crystallizes in a hexagonal molecular-type lattice, can transform into a substance with metallic properties, possibly even a superconductor. However, there is still no unambiguous data on the possibility of such a transition.
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:
H 2 + F 2 \u003d 2HF + Q.
If a mixture of hydrogen and chlorine at room temperature is irradiated with ultraviolet light, then an immediate formation of hydrogen chloride HCl is observed. The reaction of hydrogen with oxygen occurs with an explosion if a catalyst, metallic palladium (or platinum), is introduced into the mixture of these gases. When ignited, a mixture of hydrogen and oxygen (the so-called explosive gas (cm. 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 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 at elevated pressure (20-30 MPa and more) and at a temperature of 300-400 ° C in the presence of a catalyst - iron:
3H 2 + N 2 = 2NH 3 + Q.
Also, only when heated, hydrogen reacts with sulfur to form hydrogen sulfide H 2 S, with bromine - to form hydrogen bromide HBr, with iodine - 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, silicon, and phosphorus; compounds of these elements with hydrogen are obtained indirectly.
When heated, hydrogen is able to react with alkali, alkaline earth metals and magnesium to form compounds with an ionic bond character, 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, hafnium, 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, nickel, lead, tungsten, copper, etc.). So, when heated to a temperature of 400-450 ° C and above, iron 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 beyond manganese can be reduced from oxides by hydrogen. More active metals (including manganese) 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 = F, Cl, O, N), hydrogen bonds are formed between the molecules (cm. HYDROGEN BOND)(two E atoms of the same or two different elements are interconnected through the H atom: E "... N ... E"", and all three atoms are 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, etc.
Application
Hydrogen is used in the synthesis of ammonia NH 3 , 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. hydrogenation (cm. HYDROGENATION) natural vegetable oils get solid fat - margarine. Liquid hydrogen finds use as a rocket fuel and also as a coolant. A mixture of oxygen and hydrogen is used in welding.
At one time, it was suggested that in the near future, the reaction of hydrogen combustion will become the main source of energy production, and hydrogen energy will 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 harmful substances formed is minimal) 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).
Biological role
The biological significance of hydrogen is determined by the fact that it is part of water molecules and all the most important groups of natural compounds, including proteins, nucleic acids, lipids, and carbohydrates. Approximately 10% of the mass of living organisms is hydrogen. The ability of hydrogen to form a hydrogen bond plays a crucial role in maintaining the spatial quaternary structure of proteins, as well as in implementing the principle of complementarity. (cm. COMPLEMENTARY) in the construction and functions of nucleic acids (that is, in the storage and implementation of genetic information), in general, in the implementation of "recognition" at the molecular level. Hydrogen (H + ion) takes part in the most important dynamic processes and reactions in the body - in biological oxidation, which provides living cells with energy, in plant photosynthesis, in biosynthesis reactions, in nitrogen fixation and bacterial photosynthesis, in maintaining acid-base balance and homeostasis (cm. homeostasis), in membrane transport processes. Thus, along with oxygen and carbon, hydrogen forms the structural and functional basis of the phenomena of life.
encyclopedic Dictionary. 2009 .
Synonyms:See what "hydrogen" is in other dictionaries:
Table of nuclides General information Name, symbol Hydrogen 4, 4H Neutrons 3 Protons 1 Nuclide properties Atomic mass 4.027810 (110) ... Wikipedia
Table of nuclides General information Name, symbol Hydrogen 5, 5H Neutrons 4 Protons 1 Nuclide properties Atomic mass 5.035310 (110) ... Wikipedia
Table of nuclides General information Name, symbol Hydrogen 6, 6H Neutrons 5 Protons 1 Nuclide properties Atomic mass 6.044940 (280) ... Wikipedia
Table of nuclides General information Name, symbol Hydrogen 7, 7H Neutrons 6 Protons 1 Nuclide properties Atomic mass 7.052750 (1080) ... Wikipedia
History reference
Hydrogen is the first element of PSCE D.I. Mendeleev.
The Russian name for hydrogen indicates that it "gives birth to water"; Latin " hydrogenium" means the same.
For the first time, the release of combustible gas during the interaction of certain metals with acids was observed by Robert Boyle and his contemporaries in the first half of the 16th century.
But hydrogen was discovered only in 1766 by the English chemist Henry Cavendish, who found that when metals interact with dilute acids, a certain “combustible air” is released. Observing the combustion of hydrogen in air, Cavendish found that the result is water. This was in 1782.
In 1783, the French chemist Antoine-Laurent Lavoisier isolated hydrogen by decomposing water with hot iron. In 1789, hydrogen was isolated from the decomposition of water under the action of an electric current.
Prevalence in nature
Hydrogen is the main element of space. For example, the Sun is made up of 70% of its mass hydrogen. There are several tens of thousands of times more hydrogen atoms in the Universe than all the atoms of all metals combined.In the earth's atmosphere, too, there is some hydrogen in the form of a simple substance - a gas of composition H 2. Hydrogen is much lighter than air and is therefore found in the upper atmosphere.
But there is much more bound hydrogen on Earth: after all, it is part of water, the most common complex substance on our planet. Hydrogen bound into molecules contains both oil and natural gas, many minerals and rocks. Hydrogen is a constituent of all organic substances.
Characteristics of the element hydrogen.
Hydrogen has a dual nature, for this reason, in some cases, hydrogen is placed in the subgroup of alkali metals, and in others - in the subgroup of halogens.
Electronic configuration 1s 1 . A hydrogen atom consists of one proton and one electron.
The hydrogen atom is able to lose an electron and turn into an H + cation, and in this it is similar to alkali metals.
The hydrogen atom can also attach an electron, thus forming an anion H - , in this respect, hydrogen is similar to halogens.
Always monovalent in compounds
CO: +1 and -1.
Physical properties of hydrogen
Hydrogen is a gas, colorless, tasteless and odorless. 14.5 times lighter than air. Slightly soluble in water. It has high thermal conductivity. At t= -253 °C it liquefies, at t= -259 °C it solidifies. Hydrogen molecules are so small that they can slowly diffuse through many materials - rubber, glass, metals, which is used in the purification of hydrogen from other gases.Three isotopes of hydrogen are known: - protium, - deuterium, - tritium. The main part of natural hydrogen is protium. Deuterium is part of the heavy water that enriches the surface waters of the ocean. Tritium is a radioactive isotope.
Chemical properties of hydrogen
Hydrogen is a non-metal and has a molecular structure. The hydrogen molecule consists of two atoms linked by a non-polar covalent bond. The binding energy in a hydrogen molecule is 436 kJ/mol, which explains the low chemical activity of molecular hydrogen.
Interaction with halogens. At ordinary temperature, hydrogen reacts only with fluorine:
With chlorine - only in the light, forming hydrogen chloride, with bromine the reaction proceeds less vigorously, with iodine it does not go to the end even at high temperatures.
Interaction with oxygen when heated, when ignited, the reaction proceeds with an explosion: 2H 2 + O 2 \u003d 2H 2 O.
A mixture of 1 part oxygen and 2 parts hydrogen is an "explosive mixture", the most explosive.
Interaction with sulfur - when heated H 2 + S = H 2 S.
interaction with nitrogen. When heated, at high pressure and in the presence of a catalyst:
Interaction with nitric oxide (II). Used in purification systems in the production of nitric acid: 2NO + 2H 2 = N 2 + 2H 2 O.
Interaction with metal oxides. Hydrogen is a good reducing agent, it restores many metals from their oxides: CuO + H 2 = Cu + H 2 O.
Atomic hydrogen is a strong reducing agent. It is formed from molecular in an electrical discharge under low pressure conditions. It has a high restorative activity hydrogen at the time of release formed when a metal is reduced with an acid.
Interaction with active metals . At high temperature, it combines with alkali and alkaline earth metals and forms white crystalline substances - metal hydrides, showing the properties of an oxidizing agent: 2Na + H 2 = 2NaH;
Getting hydrogen
In the laboratory:
The interaction of metal with dilute solutions of sulfuric and hydrochloric acids,
The interaction of aluminum or silicon with aqueous solutions of alkalis:
Si + 2NaOH + H 2 O \u003d Na 2 SiO 3 + 2H 2.
In industry:
Electrolysis of aqueous solutions of sodium and potassium chlorides or electrolysis of water in the presence of hydroxides:
2H 2 O \u003d 2H 2 + O 2.
conversion method. First, water gas is obtained by passing water vapor through hot coke at 1000 ° C:
Then carbon monoxide (II) is oxidized to carbon monoxide (IV) by passing a mixture of water gas with excess water vapor over a Fe 2 O 3 catalyst heated to 400–450 ° C:
CO + H 2 O \u003d CO 2 + H 2.
The resulting carbon monoxide (IV) is absorbed by water, in this way 50% of industrial hydrogen is obtained.
Methane conversion: CH 4 + H 2 O \u003d CO + 3H 2.
Thermal decomposition of methane at 1200 °C: CH 4 = C + 2H 2 .
Deep cooling (down to -196 °С) of coke oven gas. At this temperature, all gaseous substances, except hydrogen, condense.
The use of hydrogen is based on its physical and chemical properties:
as a light gas, it is used to fill balloons (mixed with helium);
oxygen-hydrogen flame is used to obtain high temperatures when welding metals;
as a reducing agent is used to obtain metals (molybdenum, tungsten, etc.) from their oxides;
for the production of ammonia and artificial liquid fuels, for the hydrogenation of fats.
Exhaust free car. This is a Mirai made by Toyota. The car runs on hydrogen fuel.
Only heated air and water vapor exit the exhaust pipes. The car of the future is already on the road, although it has problems with refueling.
Although, given the prevalence of hydrogen in the universe, there should not be such a snag.
The world consists of 1 substance by three quarters. So, your serial number element hydrogen justifies. Today, all attention to him.
Properties of hydrogen
Being the first element hydrogen generates the first substance. This is water. Its formula is known to be H 2 O.
The Greek name for hydrogen is hidrogenium, where hidro is water and genium is to generate.
However, the name of the element was given not by the Greeks, but by the French naturalist Laurent Lavoisier. Before him, hydrogen was explored by Henry Quevendish, Nicola Lemery and Theophrastus Paracelsus.
The latter, in fact, left the first mention of the first substance to science. The entry is dated to the 16th century. What conclusions have scientists reached about hydrogen?
Element characteristic- duality. A hydrogen atom has only 1 electron. In a number of reactions, the substance gives it away.
This is the behavior of a typical metal from the first group. However, hydrogen is also capable of completing its shell, not giving up, but accepting 1 electron.
In this case, element 1 behaves like halogens. They are located in the 17th group of the periodic system and are prone to formation.
Which of them contains hydrogen? For example, in hydrosulfide. Its formula: - NaHS.
This compound of the element hydrogen is based on. As can be seen, the hydrogen atoms are displaced from it by sodium only partially.
The presence of just one electron and the ability to donate it turns a hydrogen atom into a proton. The nucleus also has only one particle with a positive charge.
The relative mass of a proton with an electron is 2-um. The indicator is 14 times less than that of air. Without an electron, matter is even lighter.
The conclusion that hydrogen is a gas suggests itself. But, the element also has a liquid form. Liquefaction occurs at a temperature of -252.8 degrees Celsius.
Due to their small size chemical element hydrogen has the ability to seep through other substances.
So, if you inflate the air not with helium, or with ordinary air, but with pure element No. 1, it will be blown away in a couple of days.
Gas particles will easily pass into the pores. Hydrogen also passes into some metals, for example, and.
Accumulating in their structure, the substance evaporates with increasing temperature.
Though hydrogen enters in the composition of water, it dissolves poorly. It is not for nothing that in laboratories the element is isolated by displacing moisture. And how do industrialists extract the 1st substance? We will devote the next chapter to this.
Hydrogen production
Hydrogen formula allows you to mine it at least 6 ways. The first is steam reforming of methane and natural gas.
Legroin fractions are taken. Pure hydrogen is extracted from them catalytically. This requires the presence of water vapor.
The second way to extract the 1st substance is gasification. the fuel is heated to 1500 degrees, converting into combustible gases.
This requires an oxidizing agent. Ordinary atmospheric oxygen is sufficient.
The third way to produce hydrogen is the electrolysis of water. Current is passed through it. It helps to highlight the desired element on the electrodes.
You can also use pyrolysis. This is the thermal decomposition of compounds. Both organics and inorganic substances, for example, the same water, are forced to disintegrate. The process takes place at high temperatures.
The fifth way to produce hydrogen is partial oxidation, and the sixth is biotechnology.
The latter refers to the extraction of gas from water by its biochemical splitting. Special algae help.
A closed photobioreactor is needed, therefore, the 6th method is rarely used. In fact, only the steam reforming method is popular.
It is the cheapest and easiest. However, the presence of a mass of alternatives makes hydrogen a desirable raw material for industry, because there is no dependence on a specific source of the element.
Application of hydrogen
Hydrogen is used for synthesis. This compound is a refrigerant in freezing technology, known as a component of ammonia, and is used as an acid neutralizer.
Hydrogen is also used for the synthesis of hydrochloric acid. This is the second title.
It is needed, for example, for cleaning metal surfaces, polishing them. In the food industry, hydrochloric acid is an acidity regulator E507.
Hydrogen itself is also registered as a food additive. Its name on product packaging is E949.
It is used, in particular, in the production of margarine. The hydrogenation system actually makes margarine.
In fatty vegetable oils, part of the bonds are broken. Hydrogen atoms stand up at the breakpoints. This is what transforms the fluid substance into relatively.
Cast hydrogen fuel cell it is used, so far, not so much in, but in missiles.
The first substance burns in oxygen, which gives energy for the movement of spacecraft.
Thus, one of the most powerful Russian rockets, Energia, runs on hydrogen fuel. The first element in it is liquefied.
The combustion reaction of hydrogen in oxygen is also useful in welding. You can fasten the most refractory materials.
The reaction temperature in its pure form is 3000 degrees Celsius. With the use of special it is possible to reach 4000 degrees.
"Surrender" any, any metal. By the way, metals are also obtained with the help of the 1st element. The reaction is based on the release of valuable substances from their oxides.
The nuclear industry complains isotopes of hydrogen. There are only 3 of them. One of them is tritium. He is radioactive.
There are also non-radioactive protium and deuterium. Although tritium radiates danger, it is found in the natural environment.
The isotope is formed in the upper layers of the atmosphere, which are affected by cosmic rays. This leads to nuclear reactions.
In reactors on the surface of the earth, tritium is the result of neutron irradiation.
Hydrogen price
Most often, industrialists offer gaseous hydrogen, of course, in a compressed state and in a special container that will not let small atoms of matter through.
The first element is divided into technical and refined, that is, the highest grade. There are even hydrogen brands, for example, "A".
GOST 3022-80 applies to it. This is technical gas. For 40 cubic liters, manufacturers ask for a little less than 1000. For 50 liters they give 1300.
GOST for pure hydrogen - R 51673-2000. The purity of the gas is 9.9999%. The technical element, however, is a little inferior.
Its purity is 9.99%. However, for 40 cubic liters of pure substance they give more than 13,000 rubles.
The price tag shows how difficult the final stage of gas purification is given to industrialists. For a 50-liter cylinder, you will have to pay 15,000-16,000 rubles.
liquid hydrogen almost never used. Too costly, the losses are great. Therefore, there are no offers to sell or buy.
Liquefied hydrogen is not only difficult to obtain, but also difficult to store. Temperatures of minus 252 degrees are no joke.
Therefore, no one is going to joke, using effective and easy-to-use gas.
Hydrogen(lat. Hydrogenium), H, a chemical element, the first by serial number in Mendeleev's periodic system; atomic mass 1.0079. Under ordinary conditions Hydrogen is a gas; has no color, smell and taste.
Distribution of Hydrogen in nature. Hydrogen is widely distributed in nature, its content in the earth's crust (lithosphere and hydrosphere) is 1% by mass, and 16% by the number of atoms. Hydrogen is part of the most common substance on Earth - water (11.19% Hydrogen by mass), in the compounds that make up coal, oil, natural gases, clay, as well as animal and plant organisms (that is, in the composition of proteins, nucleic acids , fats, carbohydrates, etc.). Hydrogen is extremely rare in the free state; it is found in small amounts in volcanic and other natural gases. Negligible amounts of free Hydrogen (0.0001% by number of atoms) are present in the atmosphere. In near-Earth space, Hydrogen in the form of a stream of protons forms the internal ("proton") radiation belt of the Earth. Hydrogen is the most abundant element in space. In the form of plasma, it makes up about half the mass of the Sun and most stars, the bulk of the gases of the interstellar medium and gaseous nebulae. Hydrogen is present in the atmosphere of a number of planets and in comets in the form of free H 2 , methane CH 4 , ammonia NH 3 , water H 2 O, radicals such as CH, NH, OH, SiH, PH, etc. Hydrogen enters in the form of a proton flux in the corpuscular radiation of the Sun and cosmic rays.
Isotopes, atom and molecule of Hydrogen. Ordinary Hydrogen consists of a mixture of 2 stable isotopes: light Hydrogen, or protium (1 H), and heavy Hydrogen, or deuterium (2 H, or D). In natural hydrogen compounds, there are on average 6800 atoms of 1 H per 1 atom of 2 H. A radioactive isotope with a mass number of 3 is called superheavy Hydrogen, or tritium (3 H, or T), with soft β-radiation and a half-life T ½ = 12.262 years . In nature, tritium is formed, for example, from atmospheric nitrogen under the action of cosmic ray neutrons; it is negligible in the atmosphere (4·10 -15% of the total number of hydrogen atoms). An extremely unstable isotope 4 H was obtained. The mass numbers of the isotopes 1 H, 2 H, 3 H and 4 H, respectively 1, 2, 3 and 4, indicate that the nucleus of the protium atom contains only one proton, deuterium - one proton and one neutron, tritium - one proton and 2 neutrons, 4 H - one proton and 3 neutrons. The large difference in the masses of the isotopes of Hydrogen causes a more noticeable difference in their physical and chemical properties than in the case of isotopes of other elements.
The Hydrogen atom has the simplest structure among the atoms of all other elements: it consists of a nucleus and one electron. The binding energy of an electron with a nucleus (ionization potential) is 13.595 eV. Neutral atom Hydrogen can also attach a second electron, forming a negative ion H - in this case, the binding energy of the second electron with a neutral atom (electron affinity) is 0.78 eV. Quantum mechanics makes it possible to calculate all possible energy levels of the Hydrogen atom and, consequently, to give a complete interpretation of its atomic spectrum. The Hydrogen atom is used as a model atom in quantum mechanical calculations of the energy levels of other, more complex atoms.
The Hydrogen H 2 molecule consists of two atoms connected by a covalent chemical bond. The energy of dissociation (that is, decay into atoms) is 4.776 eV. The interatomic distance at the equilibrium position of the nuclei is 0.7414Å. At high temperatures, molecular Hydrogen dissociates into atoms (the degree of dissociation at 2000°C is 0.0013; at 5000°C it is 0.95). Atomic Hydrogen is also formed in various chemical reactions (for example, by the action of Zn on hydrochloric acid). However, the existence of Hydrogen in the atomic state lasts only a short time, the atoms recombine into H 2 molecules.
Physical properties of Hydrogen. Hydrogen is the lightest of all known substances (14.4 times lighter than air), density 0.0899 g/l at 0°C and 1 atm. Hydrogen boils (liquefies) and melts (solidifies) at -252.8°C and -259.1°C, respectively (only helium has lower melting and boiling points). The critical temperature of Hydrogen is very low (-240°C), so its liquefaction is associated with great difficulties; critical pressure 12.8 kgf / cm 2 (12.8 atm), critical density 0.0312 g / cm 3. Hydrogen has the highest thermal conductivity of all gases, equal to 0.174 W/(m·K) at 0°С and 1 atm, i.e. 4.16·10 -4 cal/(s·cm·°С). The specific heat capacity of Hydrogen at 0°C and 1 atm C is 14.208 kJ/(kg K), i.e. 3.394 cal/(g°C). Hydrogen is slightly soluble in water (0.0182 ml / g at 20 ° C and 1 atm), but well - in many metals (Ni, Pt, Pa and others), especially in palladium (850 volumes per 1 volume of Pd). The solubility of Hydrogen in metals is related to its ability to diffuse through them; diffusion through a carbon alloy (for example, steel) is sometimes accompanied by the destruction of the alloy due to the interaction of Hydrogen with carbon (the so-called decarbonization). Liquid Hydrogen is very light (density at -253°C 0.0708 g/cm3) and fluid (viscosity at -253°C 13.8 centipoise).
Chemical properties of Hydrogen. In most compounds, Hydrogen exhibits a valency (more precisely, an oxidation state) of +1, like sodium and other alkali metals; usually it is considered as an analogue of these metals, heading group I of the Mendeleev system. However, in metal hydrides, the Hydrogen ion is negatively charged (oxidation state -1), that is, the Na + H - hydride is built like Na + Cl - chloride. This and some other facts (the closeness of the physical properties of Hydrogen and halogens, the ability of halogens to replace Hydrogen in organic compounds) give grounds to include Hydrogen also in group VII of the periodic system. Under normal conditions, molecular Hydrogen is relatively inactive, combining directly with only the most active nonmetals (with fluorine, and in the light also with chlorine). However, when heated, it reacts with many elements. Atomic Hydrogen has an increased chemical activity compared to molecular hydrogen. Hydrogen combines with oxygen to form water:
H 2 + 1/2 O 2 \u003d H 2 O
with the release of 285.937 kJ / mol, that is, 68.3174 kcal / mol of heat (at 25 ° C and 1 atm). At ordinary temperatures, the reaction proceeds extremely slowly, above 550 ° C - with an explosion. The explosive limits of a hydrogen-oxygen mixture are (by volume) from 4 to 94% H 2, and a hydrogen-air mixture - from 4 to 74% H 2 (a mixture of 2 volumes of H 2 and 1 volume of O 2 is called explosive gas). Hydrogen is used to reduce many metals, as it takes away oxygen from their oxides:
CuO + H 2 \u003d Cu + H 2 O,
Fe 3 O 4 + 4H 2 \u003d 3Fe + 4H 2 O, etc.
With halogens Hydrogen forms hydrogen halides, for example:
H 2 + Cl 2 \u003d 2HCl.
Hydrogen explodes with fluorine (even in the dark and at -252°C), reacts with chlorine and bromine only when illuminated or heated, and with iodine only when heated. Hydrogen reacts with nitrogen to form ammonia:
ZN 2 + N 2 \u003d 2NH 3
only on a catalyst and at elevated temperatures and pressures. When heated, Hydrogen reacts vigorously with sulfur:
H 2 + S \u003d H 2 S (hydrogen sulfide),
much more difficult with selenium and tellurium. Hydrogen can react with pure carbon without a catalyst only at high temperatures:
2H 2 + C (amorphous) = CH 4 (methane).
Hydrogen directly reacts with some metals (alkali, alkaline earth and others), forming hydrides:
H 2 + 2Li = 2LiH.
Of great practical importance are the reactions of Hydrogen with carbon monoxide (II), in which, depending on the temperature, pressure, and catalyst, various organic compounds are formed, for example, HCHO, CH 3 OH, and others. Unsaturated hydrocarbons react with Hydrogen to become saturated, for example:
C n H 2n + H 2 \u003d C n H 2n + 2.
The role of hydrogen and its compounds in chemistry is exceptionally great. Hydrogen determines the acidic properties of the so-called protic acids. Hydrogen tends to form a so-called hydrogen bond with some elements, which has a decisive influence on the properties of many organic and inorganic compounds.
Getting Hydrogen. The main types of raw materials for the industrial production of Hydrogen are natural combustible gases, coke oven gas and oil refining gases. Hydrogen is also obtained from water by electrolysis (in places with cheap electricity). The most important methods for the production of Hydrogen from natural gas are the catalytic interaction of hydrocarbons, mainly methane, with water vapor (conversion):
CH 4 + H 2 O \u003d CO + ZH 2,
and incomplete oxidation of hydrocarbons by oxygen:
CH 4 + 1/2 O 2 \u003d CO + 2H 2
The resulting carbon monoxide (II) is also subjected to conversion:
CO + H 2 O \u003d CO 2 + H 2.
Hydrogen produced from natural gas is the cheapest.
Hydrogen is isolated from coke oven gas and refinery gases by removing the remaining components of the gas mixture, which are more easily liquefied than hydrogen, upon deep cooling. The electrolysis of water is carried out with direct current, passing it through a solution of KOH or NaOH (acids are not used to avoid corrosion of steel equipment). Hydrogen is produced in laboratories by the electrolysis of water, as well as by the reaction between zinc and hydrochloric acid. However, more often they use ready-made hydrogen in cylinders.
Application of Hydrogen. Hydrogen began to be produced on an industrial scale at the end of the 18th century for filling balloons. At present, hydrogen is widely used in the chemical industry, mainly for the production of ammonia. A large consumer of hydrogen is also the production of methyl and other alcohols, synthetic gasoline and other products obtained by synthesis from hydrogen and carbon monoxide (II). Hydrogen is used for the hydrogenation of solid and heavy liquid fuels, fats and others, for the synthesis of HCl, for the hydrotreatment of petroleum products, in welding and cutting metals with an oxygen-hydrogen flame (temperature up to 2800 ° C) and in atomic hydrogen welding (up to 4000 ° C) . Hydrogen isotopes, deuterium and tritium, have found very important applications in nuclear power engineering.
Phenols
Structure
The hydroxyl group in the molecules of organic compounds can be connected directly to the aromatic nucleus, or it can be separated from it by one or more carbon atoms. It can be expected that, depending on this, the properties of substances will differ significantly from each other due to the mutual influence of groups of atoms (remember one of the provisions of Butlerov's theory). Indeed, organic compounds containing an aromatic phenyl C 6 H 5 - radical directly bonded to a hydroxyl group exhibit special properties that differ from those of alcohols. Such compounds are called phenols.
Phenols - organic substances whose molecules contain a phenyl radical associated with one or more hydroxyl groups.
Like alcohols, phenols are classified by atomicity, i.e., by the number of hydroxyl groups. Monatomic phenols contain one hydroxyl group in the molecule:
There are other polyatomic phenols containing three or more hydroxyl groups in the benzene ring.
Let's get acquainted in more detail with the structure and properties of the simplest representative of this class - phenol C6H50H. The name of this substance formed the basis for the name of the entire class - phenols.
Physical Properties
Solid colorless crystalline substance, tºpl = 43 °C, tº bp = °C, with a sharp characteristic odor. Poisonous. Phenol is slightly soluble in water at room temperature. An aqueous solution of phenol is called carbolic acid. It causes burns on contact with the skin, so phenol must be handled with care.
The structure of the phenol molecule
In the phenol molecule, the hydroxyl is directly bonded to the carbon atom of the benzene aromatic nucleus.
Let us recall the structure of the groups of atoms that form the phenol molecule.
The aromatic ring consists of six carbon atoms forming a regular hexagon due to the sp 2 hybridization of the electron orbitals of six carbon atoms. These atoms are linked by z-bonds. The p-electrons of each carbon atom not participating in the formation of st-bonds, overlapping on opposite sides of the z-bond plane, form two parts of a single six-electron P-a cloud covering the entire benzene ring (aromatic nucleus). In the C6H6 benzene molecule, the aromatic nucleus is absolutely symmetrical, a single electronic P-cloud evenly covers the ring of carbon atoms under and above the plane of the molecule (Fig. 24). The covalent bond between the oxygen and hydrogen atoms of the hydroxyl radical is strongly polar, the general electron cloud of the O-H bond is shifted towards the oxygen atom, on which a partial negative charge arises, and on the hydrogen atom, a partial positive charge. In addition, the oxygen atom in the hydroxyl group has two unshared electron pairs belonging only to it.
In a phenol molecule, the hydroxyl radical interacts with the aromatic nucleus, while the lone electron pairs of the oxygen atom interact with a single TC cloud of the benzene ring, forming a single electronic system. Such an interaction of lone electron pairs and clouds of r-bonds is called conjugation. As a result of conjugation of the lone electron pair of the oxygen atom of the hydroxy group with the electron system of the benzene ring, the electron density on the oxygen atom decreases. This decrease is compensated for by the greater polarization of the О–Н bond, which, in turn, leads to an increase in the positive charge on the hydrogen atom. Therefore, the hydrogen of the hydroxyl group in the phenol molecule has an "acidic" character.
It is logical to assume that the conjugation of the electrons of the benzene ring and the hydroxyl group affects not only its properties, but also the reactivity of the benzene ring.
In fact, as you remember, the conjugation of the lone pairs of the oxygen atom with the n-cloud of the benzene ring leads to a redistribution of the electron density in it. It decreases at the carbon atom associated with the OH group (the influence of the electron pairs of the oxygen atom affects) and increases at the carbon atoms adjacent to it (i.e., positions 2 and 6, or ortho positions). Obviously, an increase in the electron density at these carbon atoms of the benzene ring leads to the localization (concentration) of a negative charge on them. Under the influence of this charge, there is a further redistribution of electron density in the aromatic nucleus - its displacement from the 3rd and 5th atoms (.meta-position) to the 4th (ortho-position). These processes can be expressed by the scheme:
Thus, the presence of a hydroxyl radical in the phenol molecule leads to a change in the n-cloud of the benzene ring, an increase in the electron density at the 2, 4 and 6 carbon atoms (ortho-, dara-positions) and a decrease in the electron density at the 3rd and 5- th carbon atoms (meta positions).
The localization of the electron density in the ortho and para positions makes them most likely to be attacked by electrophilic particles when interacting with other substances.
Consequently, the influence of the radicals that make up the phenol molecule is mutual, and it determines its characteristic properties.
Chemical properties of phenol
Acid properties
As already mentioned, the hydrogen atom of the hydroxyl group of phenol has an acidic character. The acidic properties of phenol are more pronounced than those of water and alcohols. Unlike alcohols and water, phenol reacts not only with alkali metals, but also with alkalis to form phenolates.
However, the acidic properties of phenols are less pronounced than those of inorganic and carboxylic acids. So, for example, the acidic properties of phenol are approximately 3000 times less than those of carbonic acid. Therefore, by passing carbon dioxide through an aqueous solution of sodium phenolate, free phenol can be isolated:
The addition of hydrochloric or sulfuric acid to an aqueous solution of sodium phenolate also leads to the formation of phenol.
Qualitative reaction to phenol
Phenol reacts with iron(III) chloride to form an intensely violet colored complex compound.
This reaction makes it possible to detect it even in very small quantities. Other phenols containing one or more hydroxyl groups in the benzene ring also give a bright blue-violet color when reacted with iron(III) chloride.
Benzene ring reactions
The presence of a hydroxyl substituent greatly facilitates the course of electrophilic substitution reactions in the benzene ring.
1. Bromination of phenol. Unlike benzene, phenol bromination does not require the addition of a catalyst (iron(III) bromide).
In addition, the interaction with phenol proceeds selectively (selectively): bromine atoms are sent to the ortho and para positions, replacing the hydrogen atoms located there. The selectivity of the substitution is explained by the features of the electronic structure of the phenol molecule discussed above. So, when phenol reacts with bromine water, a white precipitate of 2,4,6-tribromophenol is formed.
This reaction, as well as the reaction with iron(III) chloride, serves for the qualitative detection of phenol.
2. Phenol nitration is also easier than benzene nitration. The reaction with dilute nitric acid proceeds at room temperature. As a result, a mixture of ortho- and para-isomers of nitrophenol is formed: 
3. Hydrogenation of the aromatic ring of phenol in the presence of a catalyst is easy.
4. Polycondensation of phenol with aldehydes, in particular, with formaldehyde, occurs with the formation of reaction products - phenol-formaldehyde resins and solid polymers.
The interaction of phenol with formaldehyde can be described by the scheme: 
You have probably noticed that “mobile” hydrogen atoms are preserved in the dimer molecule, which means that the reaction can continue further with a sufficient amount of reagents.
The polycondensation reaction, i.e., the reaction of obtaining a polymer, proceeding with the release of a low molecular weight by-product (water), can continue further (until one of the reagents is completely consumed) with the formation of huge macromolecules. The process can be described by the overall equation: 
The formation of linear molecules occurs at ordinary temperature. Carrying out this reaction when heated leads to the fact that the resulting product has a branched structure, it is solid and insoluble in water. As a result of heating a linear phenol-formaldehyde resin with an excess of aldehyde, solid plastic masses with unique properties are obtained. Polymers based on phenol-formaldehyde resins are used for the manufacture of varnishes and paints, plastic products that are resistant to heating, cooling, water, alkalis and acids, they have high dielectric properties. Polymers based on phenol-formaldehyde resins are used to make the most critical and important parts of electrical appliances, power unit cases and machine parts, the polymer base of printed circuit boards for radio devices.
Adhesives based on phenol-formaldehyde resins are able to reliably connect parts of various nature, maintaining the highest bond strength in a very wide temperature range. Such glue is used to fasten the metal base of lighting lamps to a glass bulb. Now it has become clear to you why phenol and products based on it are widely used (Scheme 8).