Hydrogen - what is this substance? Chemical and physical properties of hydrogen. Chemical Properties of Hydrogen: Features and Applications Hydrogen Chemistry invite phtml
Let's take a look at what hydrogen is. The chemical properties and production of this non-metal are studied in the course of inorganic chemistry at school. It is this element that heads the periodic system of Mendeleev, and therefore deserves a detailed description.
Brief information about opening an element
Before considering the physical and chemical properties of hydrogen, let's find out how this important element was found.
Chemists who worked in the sixteenth and seventeenth centuries repeatedly mentioned in their writings the combustible gas that is released when acids are exposed to active metals. In the second half of the eighteenth century, G. Cavendish managed to collect and analyze this gas, giving it the name "combustible gas".
The physical and chemical properties of hydrogen at that time were not studied. Only at the end of the eighteenth century, A. Lavoisier managed to establish by analysis that this gas can be obtained by analyzing water. A little later, he began to call the new element hydrogene, which means "giving birth to water." Hydrogen owes its modern Russian name to M.F. Solovyov.
Being in nature
The chemical properties of hydrogen can only be analyzed based on its abundance in nature. This element is present in the hydro- and lithosphere, and is also part of minerals: natural and associated gas, peat, oil, coal, oil shale. It is difficult to imagine an adult who would not know that hydrogen is an integral part of water.
In addition, this non-metal is found in animal organisms in the form of nucleic acids, proteins, carbohydrates, and fats. On our planet, this element is found in free form quite rarely, perhaps only in natural and volcanic gas.
In the form of plasma, hydrogen makes up about half the mass of stars and the Sun, and is also part of the interstellar gas. For example, in free form, as well as in the form of methane, ammonia, this non-metal is present in comets and even some planets.
Physical properties
Before considering the chemical properties of hydrogen, we note that under normal conditions it is a gaseous substance lighter than air, having several isotopic forms. It is almost insoluble in water and has a high thermal conductivity. Protium, which has a mass number of 1, is considered its lightest form. Tritium, which has radioactive properties, is formed in nature from atmospheric nitrogen when neurons expose it to UV rays.
Features of the structure of the molecule
To consider the chemical properties of hydrogen, the reactions characteristic of it, let us dwell on the features of its structure. This diatomic molecule has a covalent non-polar chemical bond. The formation of atomic hydrogen is possible when active metals interact with acid solutions. But in this form, this non-metal is able to exist only for an insignificant time period, almost immediately it recombines into a molecular form.
Chemical properties
Consider the chemical properties of hydrogen. In most of the compounds that this chemical element forms, it exhibits an oxidation state of +1, which makes it similar to active (alkali) metals. The main chemical properties of hydrogen, characterizing it as a metal:
- interaction with oxygen to form water;
- reaction with halogens, accompanied by the formation of hydrogen halide;
- production of hydrogen sulfide when combined with sulfur.
Below is the reaction equation that characterizes the chemical properties of hydrogen. We draw attention to the fact that as a non-metal (with an oxidation state of -1), it acts only in the reaction with active metals, forming the corresponding hydrides with them.
Hydrogen at ordinary temperature does not actively interact with other substances, so most of the reactions are carried out only after preheating.
Let us dwell in more detail on some chemical interactions of the element that heads the periodic system of chemical elements of Mendeleev.
The reaction of water formation is accompanied by the release of 285.937 kJ of energy. At elevated temperatures (more than 550 degrees Celsius), this process is accompanied by a strong explosion.
Among those chemical properties of gaseous hydrogen that have found significant application in industry, its interaction with metal oxides is of interest. It is by catalytic hydrogenation in modern industry that metal oxides are processed, for example, pure metal is isolated from iron scale (mixed iron oxide). This method allows for efficient processing of scrap metal.
The synthesis of ammonia, which involves the interaction of hydrogen with atmospheric nitrogen, is also in demand in the modern chemical industry. Among the conditions for the occurrence of this chemical interaction, we note pressure and temperature.
Conclusion
It is hydrogen that is an inactive chemical substance under normal conditions. As the temperature rises, its activity increases significantly. This substance is in demand in organic synthesis. For example, by hydrogenation, ketones can be reduced to secondary alcohols, and aldehydes can be converted to primary alcohols. In addition, by hydrogenation, unsaturated hydrocarbons of the ethylene and acetylene classes can be converted into saturated compounds of the methane series. Hydrogen is rightly considered a simple substance in demand in modern chemical production.
Hydrogen H is a chemical element, one of the most common in our universe. The mass of hydrogen as an element in the composition of substances is 75% of the total content of atoms of another type. It is included in the most important and vital connection on the planet - water. A distinctive feature of hydrogen is also that it is the first element in the periodic system of chemical elements of D. I. Mendeleev.
Discovery and exploration
The first references to hydrogen in the writings of Paracelsus date back to the sixteenth century. But its isolation from the gas mixture of air and the study of combustible properties were already made in the seventeenth century by the scientist Lemery. Hydrogen was thoroughly studied by an English chemist, physicist and naturalist who experimentally proved that the mass of hydrogen is the smallest in comparison with other gases. In the subsequent stages of the development of science, many scientists worked with him, in particular Lavoisier, who called him "giving birth to water."
Characteristic according to the position in the PSCE
The element that opens the periodic table of D. I. Mendeleev is hydrogen. The physical and chemical properties of the atom show some duality, since the hydrogen is simultaneously assigned to the first group, the main subgroup, if it behaves like a metal and gives up a single electron in the process of a chemical reaction, and to the seventh - in the case of complete filling of the valence shell, that is, reception negative particle, which characterizes it as similar to halogens.
Features of the electronic structure of the element
The properties of the complex substances in which it is included, and the simplest substance H 2 are primarily determined by the electronic configuration of the hydrogen. The particle has one electron with Z= (-1), which rotates in its orbit around the nucleus, containing one proton with unit mass and positive charge (+1). Its electronic configuration is written as 1s 1, which means the presence of one negative particle in the very first and only s-orbital for the hydrogen.
When an electron is detached or given away, and an atom of this element has such a property that it is related to metals, a cation is obtained. In fact, the hydrogen ion is a positive elementary particle. Therefore, a hydrogen devoid of an electron is simply called a proton.
Physical properties
Briefly describing hydrogen, it is a colorless, slightly soluble gas with a relative atomic mass of 2, 14.5 times lighter than air, with a liquefaction temperature of -252.8 degrees Celsius.
It can be easily seen from experience that H2 is the lightest. To do this, it is enough to fill three balls with various substances - hydrogen, carbon dioxide, ordinary air - and simultaneously release them from your hand. The one that is filled with CO 2 will reach the ground faster than anyone, after which it will fall inflated with an air mixture, and the one containing H 2 will rise to the ceiling.
The small mass and size of hydrogen particles justify its ability to penetrate through various substances. On the example of the same ball, this is easy to verify, in a couple of days it will deflate itself, since the gas will simply pass through the rubber. Also, hydrogen can accumulate in the structure of some metals (palladium or platinum), and evaporate from it when the temperature rises.
The property of low solubility of hydrogen is used in laboratory practice to isolate it by the method of hydrogen displacement (the table below contains the main parameters) determine the scope of its application and methods of production.
| Parameter of an atom or molecule of a simple substance | Meaning |
| Atomic mass (molar mass) | 1.008 g/mol |
| Electronic configuration | 1s 1 |
| Crystal cell | Hexagonal |
| Thermal conductivity | (300 K) 0.1815 W/(m K) |
| Density at n. y. | 0.08987 g/l |
| Boiling temperature | -252.76°C |
| Specific heat of combustion | 120.9 10 6 J/kg |
| Melting temperature | -259.2°C |
| Solubility in water | 18.8 ml/l |
Isotopic composition
Like many other representatives of the periodic system of chemical elements, hydrogen has several natural isotopes, that is, atoms with the same number of protons in the nucleus, but a different number of neutrons - particles with zero charge and unit mass. Examples of atoms that have a similar property are oxygen, carbon, chlorine, bromine and others, including radioactive ones.
The physical properties of hydrogen 1 H, the most common of the representatives of this group, differ significantly from the same characteristics of its counterparts. In particular, the characteristics of the substances in which they are included differ. So, there is ordinary and deuterated water, containing in its composition, instead of a hydrogen atom with a single proton, deuterium 2 H - its isotope with two elementary particles: positive and uncharged. This isotope is twice as heavy as ordinary hydrogen, which explains the fundamental difference in the properties of the compounds they make up. In nature, deuterium is 3200 times rarer than hydrogen. The third representative is tritium 3 H, in the nucleus it has two neutrons and one proton.
Methods for obtaining and isolating
Laboratory and industrial methods are very different. So, in small quantities, gas is obtained mainly through reactions in which minerals are involved, and large-scale production uses organic synthesis to a greater extent.
The following chemical interactions are used in the laboratory:
In industrial interests, gas is obtained by such methods as:
- Thermal decomposition of methane in the presence of a catalyst to its constituent simple substances (350 degrees reaches the value of such an indicator as temperature) - hydrogen H 2 and carbon C.
- Passing vaporous water through coke at 1000 degrees Celsius with the formation of carbon dioxide CO 2 and H 2 (the most common method).
- Conversion of gaseous methane on a nickel catalyst at a temperature reaching 800 degrees.
- Hydrogen is a by-product in the electrolysis of aqueous solutions of potassium or sodium chlorides.
Chemical interactions: general provisions
The physical properties of hydrogen largely explain its behavior in reaction processes with one or another compound. The valency of the hydrogen is 1, since it is located in the first group in the periodic table, and the degree of oxidation shows a different one. In all compounds, except for hydrides, hydrogen in s.o. = (1+), in molecules like XH, XH 2, XH 3 - (1-).
The hydrogen gas molecule, formed by creating a generalized electron pair, consists of two atoms and is quite stable energetically, which is why under normal conditions it is somewhat inert and enters into reactions when normal conditions change. Depending on the degree of oxidation of hydrogen in the composition of other substances, it can act both as an oxidizing agent and a reducing agent.
Substances with which hydrogen reacts and forms
Elemental interactions to form complex substances (often at elevated temperatures):
- Alkaline and alkaline earth metal + hydrogen = hydride.
- Halogen + H 2 = hydrogen halide.
- Sulfur + hydrogen = hydrogen sulfide.
- Oxygen + H 2 = water.
- Carbon + hydrogen = methane.
- Nitrogen + H 2 = ammonia.
Interaction with complex substances:
- Obtaining synthesis gas from carbon monoxide and hydrogen.
- Recovery of metals from their oxides with H 2 .
- Hydrogen saturation of unsaturated aliphatic hydrocarbons.
hydrogen bond
The physical properties of hydrogen are such that, when combined with an electronegative element, it allows it to form a special type of bond with the same atom from neighboring molecules that have unshared electron pairs (for example, oxygen, nitrogen and fluorine). The clearest example on which it is better to consider such a phenomenon is water. It can be said that it is stitched with hydrogen bonds, which are weaker than covalent or ionic ones, but due to the fact that there are many of them, they have a significant effect on the properties of the substance. Essentially, hydrogen bonding is an electrostatic interaction that binds water molecules into dimers and polymers, giving rise to its high boiling point.
Hydrogen in the composition of mineral compounds
All contain a proton - a cation of an atom such as hydrogen. A substance whose acid residue has an oxidation state greater than (-1) is called a polybasic compound. It contains several hydrogen atoms, which makes dissociation in aqueous solutions multi-stage. Each subsequent proton breaks away from the rest of the acid more and more difficult. According to the quantitative content of hydrogens in the medium, its acidity is determined.
Application in human activities
Cylinders with a substance, as well as containers with other liquefied gases, such as oxygen, have a specific appearance. They are painted dark green with a bright red "Hydrogen" lettering. Gas is pumped into a cylinder under a pressure of about 150 atmospheres. The physical properties of hydrogen, in particular the lightness of the gaseous state of aggregation, are used to fill balloons, balloons, etc. mixed with helium.
Hydrogen, the physical and chemical properties of which people learned to use many years ago, is currently used in many industries. Most of it goes to the production of ammonia. Also, hydrogen is involved in (hafnium, germanium, gallium, silicon, molybdenum, tungsten, zirconium and others) from oxides, acting in the reaction as a reducing agent, hydrocyanic and hydrochloric acids, as well as artificial liquid fuel. The food industry uses it to convert vegetable oils into solid fats.
We determined the chemical properties and use of hydrogen in various processes of hydrogenation and hydrogenation of fats, coals, hydrocarbons, oils and fuel oil. With the help of it, precious stones, incandescent lamps are produced, metal products are forged and welded under the influence of an oxygen-hydrogen flame.
Hydrogen was discovered in the second half of the 18th century by the English scientist in the field of physics and chemistry G. Cavendish. He managed to isolate a substance in a pure state, began to study it and described its properties.
Such is the history of the discovery of hydrogen. During the experiments, the researcher determined that it is a combustible gas, the combustion of which in air gives water. This led to the determination of the qualitative composition of water.
What is hydrogen
Hydrogen, as a simple substance, was first declared by the French chemist A. Lavoisier in 1784, since he determined that its molecule contains atoms of the same type.
The name of the chemical element in Latin sounds like hydrogenium (read "hydrogenium"), which means "giving birth to water." The name refers to the combustion reaction that produces water.
Characterization of hydrogen
The designation of hydrogen N. Mendeleev assigned this chemical element the first serial number, placing it in the main subgroup of the first group and the first period and conditionally in the main subgroup of the seventh group.
The atomic weight (atomic mass) of hydrogen is 1.00797. The molecular weight of H 2 is 2 a. e. The molar mass is numerically equal to it.
It is represented by three isotopes with a special name: the most common protium (H), heavy deuterium (D), and radioactive tritium (T).
It is the first element that can be completely separated into isotopes in a simple way. It is based on the high mass difference of isotopes. The process was first carried out in 1933. This is explained by the fact that only in 1932 was an isotope with a mass of 2 discovered.
Physical properties
Under normal conditions, a simple substance hydrogen in the form of diatomic molecules is a gas, without color, which has no taste and smell. Slightly soluble in water and other solvents.
Crystallization temperature - 259.2 o C, boiling point - 252.8 o C. The diameter of hydrogen molecules is so small that they have the ability to slowly diffuse through a number of materials (rubber, glass, metals). This property is used when it is required to purify hydrogen from gaseous impurities. At n. y. hydrogen has a density of 0.09 kg/m3.
Is it possible to convert hydrogen into a metal by analogy with the elements located in the first group? Scientists have found that hydrogen, under conditions when the pressure approaches 2 million atmospheres, begins to absorb infrared rays, which indicates the polarization of the molecules of the substance. Perhaps at even higher pressures, hydrogen will become a metal.
It is interesting: there is an assumption that on the giant planets, Jupiter and Saturn, hydrogen is in the form of a metal. It is assumed that metallic solid hydrogen is also present in the composition of the earth's core, due to the ultra-high pressure created by the earth's mantle.
Chemical properties
Both simple and complex substances enter into chemical interaction with hydrogen. But the low activity of hydrogen needs to be increased by creating appropriate conditions - raising the temperature, using catalysts, etc.
When heated, simple substances such as oxygen (O 2), chlorine (Cl 2), nitrogen (N 2), sulfur (S) react with hydrogen.
If you set fire to pure hydrogen at the end of the gas tube in the air, it will burn evenly, but barely noticeable. If, however, the gas outlet tube is placed in an atmosphere of pure oxygen, then combustion will continue with the formation of water drops on the walls of the vessel, as a result of the reaction:
The combustion of water is accompanied by the release of a large amount of heat. This is an exothermic compound reaction in which hydrogen is oxidized by oxygen to form the oxide H 2 O. It is also a redox reaction in which hydrogen is oxidized and oxygen is reduced.
Similarly, the reaction with Cl 2 occurs with the formation of hydrogen chloride.
The interaction of nitrogen with hydrogen requires high temperature and high pressure, as well as the presence of a catalyst. The result is ammonia.
As a result of the reaction with sulfur, hydrogen sulfide is formed, the recognition of which facilitates the characteristic smell of rotten eggs.
The oxidation state of hydrogen in these reactions is +1, and in the hydrides described below, it is 1.
When reacting with some metals, hydrides are formed, for example, sodium hydride - NaH. Some of these complex compounds are used as fuel for rockets, as well as in fusion power.
Hydrogen also reacts with substances from the complex category. For example, with copper (II) oxide, the formula CuO. To carry out the reaction, copper hydrogen is passed over heated powdered copper (II) oxide. In the course of interaction, the reagent changes its color and becomes red-brown, and droplets of water settle on the cold walls of the test tube.
During the reaction, hydrogen is oxidized to form water, and copper is reduced from oxide to a simple substance (Cu).
Areas of use
Hydrogen is of great importance for humans and is used in a variety of areas:
- In the chemical industry it is raw materials, in other industries it is fuel. Do not do without hydrogen and the enterprises of petrochemistry and oil refining.
- In the electric power industry, this simple substance acts as a cooling agent.
- In ferrous and non-ferrous metallurgy, hydrogen plays the role of a reducing agent.
- With this help, an inert environment is created when packaging products.
- The pharmaceutical industry uses hydrogen as a reagent in the production of hydrogen peroxide.
- Meteorological probes are filled with this light gas.
- This element is also known as a fuel reducing agent for rocket engines.
Scientists unanimously predict that hydrogen fuel will be the leader in the energy sector.
Receipt in industry
In industry, hydrogen is produced by electrolysis, which is subjected to chlorides or hydroxides of alkali metals dissolved in water. It is also possible to obtain hydrogen in this way directly from water.
For this purpose, the conversion of coke or methane with steam is used. The decomposition of methane at elevated temperature also produces hydrogen. The liquefaction of coke oven gas by the fractional method is also used for the industrial production of hydrogen.
Obtaining in the laboratory
In the laboratory, a Kipp apparatus is used to produce hydrogen.
Hydrochloric or sulfuric acid and zinc act as reagents. As a result of the reaction, hydrogen is formed.
Finding hydrogen in nature
Hydrogen is the most common element in the universe. The bulk of stars, including the Sun, and other cosmic bodies is hydrogen.
It is only 0.15% in the earth's crust. It is present in many minerals, in all organic substances, as well as in water that covers 3/4 of the surface of our planet.
In the upper atmosphere, traces of pure hydrogen can be found. It is also found in a number of combustible natural gases.
Gaseous hydrogen is the thinnest, and liquid hydrogen is the densest substance on our planet. With the help of hydrogen, you can change the timbre of the voice, if you inhale it, and speak as you exhale.
The most powerful hydrogen bomb is based on the splitting of the lightest atom.
The hydrogen atom has the electronic formula of the outer (and only) electronic level 1 s one . On the one hand, by the presence of one electron in the outer electronic level, the hydrogen atom is similar to alkali metal atoms. However, just like halogens, it lacks only one electron to fill the external electronic level, since no more than 2 electrons can be located on the first electronic level. It turns out that hydrogen can be placed simultaneously in both the first and the penultimate (seventh) group of the periodic table, which is sometimes done in various versions of the periodic system:
From the point of view of the properties of hydrogen as a simple substance, it nevertheless has more in common with halogens. Hydrogen, as well as halogens, is a non-metal and forms diatomic molecules (H 2) similarly to them.
Under normal conditions, hydrogen is a gaseous, inactive substance. The low activity of hydrogen is explained by the high strength of the bond between hydrogen atoms in the molecule, which requires either strong heating or the use of catalysts, or both at the same time, to break it.
Interaction of hydrogen with simple substances
with metals
Of the metals, hydrogen reacts only with alkali and alkaline earth! Alkali metals include metals of the main subgroup of group I (Li, Na, K, Rb, Cs, Fr), and alkaline earth metals are metals of the main subgroup of group II, except for beryllium and magnesium (Ca, Sr, Ba, Ra)
When interacting with active metals, hydrogen exhibits oxidizing properties, i.e. lowers its oxidation state. In this case, hydrides of alkali and alkaline earth metals are formed, which have an ionic structure. The reaction proceeds when heated:
It should be noted that interaction with active metals is the only case when molecular hydrogen H2 is an oxidizing agent.
with non-metals
Of non-metals, hydrogen reacts only with carbon, nitrogen, oxygen, sulfur, selenium and halogens!
Carbon should be understood as graphite or amorphous carbon, since diamond is an extremely inert allotropic modification of carbon.
When interacting with non-metals, hydrogen can only perform the function of a reducing agent, that is, it can only increase its oxidation state:
Interaction of hydrogen with complex substances
with metal oxides
Hydrogen does not react with metal oxides that are in the activity series of metals up to aluminum (inclusive), however, it is able to reduce many metal oxides to the right of aluminum when heated:
with non-metal oxides
Of the non-metal oxides, hydrogen reacts when heated with oxides of nitrogen, halogens, and carbon. Of all the interactions of hydrogen with non-metal oxides, its reaction with carbon monoxide CO should be especially noted.
The mixture of CO and H 2 even has its own name - “synthesis gas”, since, depending on the conditions, such demanded industrial products as methanol, formaldehyde and even synthetic hydrocarbons can be obtained from it:
with acids
Hydrogen does not react with inorganic acids!
Of the organic acids, hydrogen reacts only with unsaturated acids, as well as with acids containing functional groups capable of being reduced by hydrogen, in particular aldehyde, keto or nitro groups.
with salts
In the case of aqueous solutions of salts, their interaction with hydrogen does not occur. However, when hydrogen is passed over solid salts of some metals of medium and low activity, their partial or complete reduction is possible, for example:
Chemical properties of halogens
Halogens are the chemical elements of group VIIA (F, Cl, Br, I, At), as well as the simple substances they form. Hereinafter, unless otherwise stated, halogens will be understood as simple substances.
All halogens have a molecular structure, which leads to low melting and boiling points of these substances. Halogen molecules are diatomic, i.e. their formula can be written in general form as Hal 2 .
It should be noted such a specific physical property of iodine as its ability to sublimation or, in other words, sublimation. sublimation, they call the phenomenon in which a substance in the solid state does not melt when heated, but, bypassing the liquid phase, immediately passes into the gaseous state.
The electronic structure of the external energy level of an atom of any halogen has the form ns 2 np 5, where n is the period number of the periodic table in which the halogen is located. As you can see, only one electron is missing from the eight-electron outer shell of the halogen atoms. From this it is logical to assume the predominantly oxidizing properties of free halogens, which is also confirmed in practice. As you know, the electronegativity of non-metals decreases when moving down the subgroup, and therefore the activity of halogens decreases in the series:
F 2 > Cl 2 > Br 2 > I 2
Interaction of halogens with simple substances
All halogens are highly reactive and react with most simple substances. However, it should be noted that fluorine, due to its extremely high reactivity, can react even with those simple substances with which other halogens cannot react. Such simple substances include oxygen, carbon (diamond), nitrogen, platinum, gold, and some noble gases (xenon and krypton). Those. actually, fluorine does not react only with some noble gases.
The remaining halogens, i.e. chlorine, bromine and iodine are also active substances, but less active than fluorine. They react with almost all simple substances except oxygen, nitrogen, carbon in the form of diamond, platinum, gold and noble gases.
Interaction of halogens with non-metals
hydrogen
All halogens react with hydrogen to form hydrogen halides with the general formula HHal. At the same time, the reaction of fluorine with hydrogen begins spontaneously even in the dark and proceeds with an explosion in accordance with the equation:
The reaction of chlorine with hydrogen can be initiated by intense ultraviolet irradiation or heating. Also leaks with an explosion:
Bromine and iodine react with hydrogen only when heated, and at the same time, the reaction with iodine is reversible:
phosphorus
The interaction of fluorine with phosphorus leads to the oxidation of phosphorus to the highest oxidation state (+5). In this case, the formation of phosphorus pentafluoride occurs:
When chlorine and bromine interact with phosphorus, it is possible to obtain phosphorus halides both in the + 3 oxidation state and in the + 5 oxidation state, which depends on the proportions of the reactants:
In the case of white phosphorus in an atmosphere of fluorine, chlorine or liquid bromine, the reaction begins spontaneously.
The interaction of phosphorus with iodine can lead to the formation of only phosphorus triiodide due to the significantly lower oxidizing ability than other halogens:
gray
Fluorine oxidizes sulfur to the highest oxidation state +6, forming sulfur hexafluoride:
Chlorine and bromine react with sulfur, forming compounds containing sulfur in oxidation states that are extremely unusual for it +1 and +2. These interactions are very specific, and to pass the exam in chemistry, the ability to write down the equations of these interactions is not necessary. Therefore, the following three equations are given rather for guidance:
Interaction of halogens with metals
As mentioned above, fluorine is able to react with all metals, even such inactive ones as platinum and gold:
The remaining halogens react with all metals except platinum and gold:
Reactions of halogens with complex substances
Substitution reactions with halogens
More active halogens, i.e. the chemical elements of which are located higher in the periodic table, are able to displace less active halogens from the hydrohalic acids and metal halides they form:
Similarly, bromine and iodine displace sulfur from solutions of sulfides and or hydrogen sulfide:
Chlorine is a stronger oxidizing agent and oxidizes hydrogen sulfide in its aqueous solution not to sulfur, but to sulfuric acid:
Interaction of halogens with water
Water burns in fluorine with a blue flame in accordance with the reaction equation:
Bromine and chlorine react differently with water than fluorine. If fluorine acted as an oxidizing agent, then chlorine and bromine disproportionate in water, forming a mixture of acids. In this case, the reactions are reversible:
The interaction of iodine with water proceeds to such an insignificant degree that it can be neglected and considered that the reaction does not proceed at all.
Interaction of halogens with alkali solutions
Fluorine, when interacting with an aqueous solution of alkali, again acts as an oxidizing agent:
The ability to write this equation is not required to pass the exam. It is enough to know the fact about the possibility of such an interaction and the oxidizing role of fluorine in this reaction.
Unlike fluorine, the remaining halogens disproportionate in alkali solutions, that is, they simultaneously increase and decrease their oxidation state. At the same time, in the case of chlorine and bromine, depending on the temperature, flow in two different directions is possible. In particular, in the cold, the reactions proceed as follows:
and when heated:
Iodine reacts with alkalis exclusively according to the second option, i.e. with the formation of iodate, because hypoiodite is unstable not only when heated, but also at ordinary temperatures and even in the cold.
DEFINITION
Hydrogen- the first element of the Periodic system of chemical elements of D.I. Mendeleev. The symbol is N.
Atomic mass - 1 a.m.u. The hydrogen molecule is diatomic - H 2.
The electronic configuration of the hydrogen atom is 1s 1. Hydrogen belongs to the s-element family. In its compounds, it exhibits oxidation states -1, 0, +1. Natural hydrogen consists of two stable isotopes - protium 1 H (99.98%) and deuterium 2 H (D) (0.015%) - and a radioactive isotope of tritium 3 H (T) (trace amounts, half-life - 12.5 years) .
Chemical properties of hydrogen
Under normal conditions, molecular hydrogen exhibits a relatively low reactivity, which is explained by the high bond strength in the molecule. When heated, it interacts with almost all simple substances formed by elements of the main subgroups (except for noble gases, B, Si, P, Al). In chemical reactions, it can act both as a reducing agent (more often) and an oxidizing agent (less often).
Hydrogen manifests reducing agent properties(H 2 0 -2e → 2H +) in the following reactions:
1. Reactions of interaction with simple substances - non-metals. Hydrogen reacts with halogens, moreover, the reaction of interaction with fluorine under normal conditions, in the dark, with an explosion, with chlorine - under illumination (or UV irradiation) by a chain mechanism, with bromine and iodine only when heated; oxygen(a mixture of oxygen and hydrogen in a 2:1 volume ratio is called "explosive gas"), gray, nitrogen and carbon:
H 2 + Hal 2 \u003d 2HHal;
2H 2 + O 2 \u003d 2H 2 O + Q (t);
H 2 + S \u003d H 2 S (t \u003d 150 - 300C);
3H 2 + N 2 ↔ 2NH 3 (t = 500C, p, kat = Fe, Pt);
2H 2 + C ↔ CH 4 (t, p, kat).
2. Reactions of interaction with complex substances. Hydrogen reacts with oxides of low-active metals, and it is able to reduce only metals that are in the activity series to the right of zinc:
CuO + H 2 \u003d Cu + H 2 O (t);
Fe 2 O 3 + 3H 2 \u003d 2Fe + 3H 2 O (t);
WO 3 + 3H 2 \u003d W + 3H 2 O (t).
Hydrogen reacts with non-metal oxides:
H 2 + CO 2 ↔ CO + H 2 O (t);
2H 2 + CO ↔ CH 3 OH (t = 300C, p = 250 - 300 atm., kat = ZnO, Cr 2 O 3).
Hydrogen enters into hydrogenation reactions with organic compounds of the class of cycloalkanes, alkenes, arenes, aldehydes and ketones, etc. All these reactions are carried out under heating, under pressure, platinum or nickel is used as catalysts:
CH 2 \u003d CH 2 + H 2 ↔ CH 3 -CH 3;
C 6 H 6 + 3H 2 ↔ C 6 H 12;
C 3 H 6 + H 2 ↔ C 3 H 8;
CH 3 CHO + H 2 ↔ CH 3 -CH 2 -OH;
CH 3 -CO-CH 3 + H 2 ↔ CH 3 -CH (OH) -CH 3.
Hydrogen as an oxidizing agent(H 2 + 2e → 2H -) acts in reactions with alkali and alkaline earth metals. In this case, hydrides are formed - crystalline ionic compounds in which hydrogen exhibits an oxidation state of -1.
2Na + H 2 ↔ 2NaH (t, p).
Ca + H 2 ↔ CaH 2 (t, p).
Physical properties of hydrogen
Hydrogen is a light colorless gas, odorless, density at n.o. - 0.09 g / l, 14.5 times lighter than air, t bale = -252.8C, t pl = - 259.2C. Hydrogen is poorly soluble in water and organic solvents, it is highly soluble in some metals: nickel, palladium, platinum.
According to modern cosmochemistry, hydrogen is the most abundant element in the universe. The main form of existence of hydrogen in outer space is individual atoms. Hydrogen is the 9th most abundant element on Earth. The main amount of hydrogen on Earth is in a bound state - in the composition of water, oil, natural gas, coal, etc. In the form of a simple substance, hydrogen is rarely found - in the composition of volcanic gases.
Getting hydrogen
There are laboratory and industrial methods for producing hydrogen. Laboratory methods include the interaction of metals with acids (1), as well as the interaction of aluminum with aqueous solutions of alkalis (2). Among the industrial methods for producing hydrogen, the electrolysis of aqueous solutions of alkalis and salts (3) and the conversion of methane (4) play an important role:
Zn + 2HCl = ZnCl 2 + H 2 (1);
2Al + 2NaOH + 6H 2 O = 2Na +3 H 2 (2);
2NaCl + 2H 2 O = H 2 + Cl 2 + 2NaOH (3);
CH 4 + H 2 O ↔ CO + H 2 (4).
Examples of problem solving
EXAMPLE 1
| Exercise | When 23.8 g of metallic tin interacted with an excess of hydrochloric acid, hydrogen was released, in an amount sufficient to obtain 12.8 g of metallic copper. Determine the oxidation state of tin in the resulting compound. |
| Solution | Based on the electronic structure of the tin atom (...5s 2 5p 2), we can conclude that tin is characterized by two oxidation states - +2, +4. Based on this, we will compose the equations of possible reactions: Sn + 2HCl = H 2 + SnCl 2 (1); Sn + 4HCl = 2H 2 + SnCl 4 (2); CuO + H 2 \u003d Cu + H 2 O (3). Find the amount of copper substance: v (Cu) \u003d m (Cu) / M (Cu) \u003d 12.8 / 64 \u003d 0.2 mol. According to equation 3, the amount of hydrogen substance: v (H 2) \u003d v (Cu) \u003d 0.2 mol. Knowing the mass of tin, we find its amount of substance: v (Sn) \u003d m (Sn) / M (Sn) \u003d 23.8 / 119 \u003d 0.2 mol. Let's compare the amounts of tin and hydrogen substances according to equations 1 and 2 and according to the condition of the problem: v 1 (Sn): v 1 (H 2) = 1:1 (equation 1); v 2 (Sn): v 2 (H 2) = 1:2 (equation 2); v(Sn): v(H 2) = 0.2:0.2 = 1:1 (problem condition). Therefore, tin reacts with hydrochloric acid according to equation 1 and the oxidation state of tin is +2. |
| Answer | The oxidation state of tin is +2. |
EXAMPLE 2
| Exercise | The gas released by the action of 2.0 g of zinc per 18.7 ml of 14.6% hydrochloric acid (solution density 1.07 g/ml) was passed by heating over 4.0 g of copper (II) oxide. What is the mass of the resulting solid mixture? |
| Solution | When zinc reacts with hydrochloric acid, hydrogen is released: Zn + 2HCl \u003d ZnCl 2 + H 2 (1), which, when heated, reduces copper (II) oxide to copper (2): CuO + H 2 \u003d Cu + H 2 O. Find the amount of substances in the first reaction: m (p-ra Hcl) = 18.7. 1.07 = 20.0 g; m(HCl) = 20.0. 0.146 = 2.92 g; v (HCl) \u003d 2.92 / 36.5 \u003d 0.08 mol; v(Zn) = 2.0/65 = 0.031 mol. Zinc is deficient, so the amount of hydrogen released is: v (H 2) \u003d v (Zn) \u003d 0.031 mol. In the second reaction, hydrogen is deficient because: v (CuO) \u003d 4.0 / 80 \u003d 0.05 mol. As a result of the reaction, 0.031 mol of CuO will turn into 0.031 mol of Cu, and the mass loss will be: m (СuО) - m (Сu) \u003d 0.031 × 80 - 0.031 × 64 \u003d 0.50 g. The mass of the solid mixture of CuO with Cu after passing hydrogen will be: 4.0-0.5 = 3.5 g |
| Answer | The mass of the solid mixture of CuO with Cu is 3.5 g. |
