The purpose of the lesson. In this lesson, you will learn about perhaps the most important chemical elements for life on earth - hydrogen and oxygen, learn about their chemical properties, as well as the physical properties of the simple substances they form, learn more about the role of oxygen and hydrogen in nature and life person.
Hydrogen is the most abundant element in the universe. Oxygen is the most abundant element on earth. Together they form water, a substance that makes up more than half of the mass of the human body. Oxygen is the gas we need to breathe, and without water we could not live even a few days, so without a doubt, oxygen and hydrogen can be considered the most important chemical elements necessary for life.
The structure of hydrogen and oxygen atoms
Thus, hydrogen exhibits non-metallic properties. In nature, hydrogen occurs in the form of three isotopes, protium, deuterium and tritium, hydrogen isotopes are very different from each other in physical properties, so they are even assigned individual symbols.
If you do not remember or do not know what isotopes are, work with the materials of the electronic educational resource "Isotopes as varieties of atoms of one chemical element." In it, you will learn how the isotopes of one element differ from each other, what the presence of several isotopes in one element leads to, and also get acquainted with the isotopes of several elements.
Thus, the possible oxidation states of oxygen are limited to values from –2 to +2. If oxygen accepts two electrons (becoming an anion) or forms two covalent bonds with less electronegative elements, it goes into the -2 oxidation state. If oxygen forms one bond with another oxygen atom, and the second with an atom of a less electronegative element, it goes into the -1 oxidation state. By forming two covalent bonds with fluorine (the only element with a higher electronegativity value), oxygen goes into the +2 oxidation state. Forming one bond with another oxygen atom, and the second with a fluorine atom - +1. Finally, if oxygen forms one bond with a less electronegative atom and a second bond with fluorine, it will be in oxidation state 0.
Physical properties of hydrogen and oxygen, allotropy of oxygen
Hydrogen- colorless gas without taste and smell. Very light (14.5 times lighter than air). The temperature of hydrogen liquefaction - -252.8 ° C - is almost the lowest among all gases (second only to helium). Liquid and solid hydrogen are very light, colorless substances.
Oxygen It is a colorless, odorless, tasteless gas, slightly heavier than air. At -182.9 °C it turns into a heavy blue liquid, at -218 °C it solidifies with the formation of blue crystals. Oxygen molecules are paramagnetic, which means that oxygen is attracted to a magnet. Oxygen is poorly soluble in water.
Unlike hydrogen, which forms molecules of only one type, oxygen exhibits allotropy and forms molecules of two types, that is, the element oxygen forms two simple substances: oxygen and ozone.
Chemical properties and obtaining simple substances
Hydrogen.
The bond in the hydrogen molecule is single, but it is one of the strongest single bonds in nature, and it takes a lot of energy to break it, for this reason hydrogen is very inactive at room temperature, however, when the temperature rises (or in the presence of a catalyst), hydrogen easily interacts with many simple and complex substances.
Hydrogen is a typical non-metal from a chemical point of view. That is, it is able to interact with active metals to form hydrides, in which it exhibits an oxidation state of -1. With some metals (lithium, calcium), the interaction proceeds even at room temperature, but rather slowly, therefore, heating is used in the synthesis of hydrides:
,
.
The formation of hydrides by direct interaction of simple substances is possible only for active metals. Already aluminum does not interact directly with hydrogen, its hydride is obtained by exchange reactions.
Hydrogen also reacts with non-metals only when heated. Exceptions are the halogens chlorine and bromine, the reaction with which can be induced by light:
.
The reaction with fluorine also does not require heating; it proceeds with an explosion even with strong cooling and in absolute darkness.
The reaction with oxygen proceeds according to a branched chain mechanism, therefore the reaction rate increases rapidly, and in a mixture of oxygen and hydrogen in a ratio of 1: 2, the reaction proceeds with an explosion (such a mixture is called "explosive gas"):
.
The reaction with sulfur proceeds much more quietly, with little or no heat release:
.
Reactions with nitrogen and iodine proceed reversibly:
,
.
This circumstance greatly complicates the production of ammonia in industry: the process requires the use of elevated pressure to mix the equilibrium in the direction of ammonia formation. Hydrogen iodine is not obtained by direct synthesis, since there are several much more convenient methods for its synthesis.
Hydrogen does not directly react with low-active non-metals (), although its compounds with them are known.
In reactions with complex substances, hydrogen in most cases acts as a reducing agent. In solutions, hydrogen can reduce low-active metals (located after hydrogen in the series of voltages) from their salts:
When heated, hydrogen can reduce many metals from their oxides. Moreover, the more active the metal, the more difficult it is to restore it and the higher the temperature required for this:
.
Metals more active than zinc are practically impossible to reduce with hydrogen.
Hydrogen is produced in the laboratory by reacting metals with strong acids. The most commonly used zinc and hydrochloric acid:
Less commonly used electrolysis of water in the presence of strong electrolytes:
In industry, hydrogen is produced as a by-product in the production of caustic soda by electrolysis of a sodium chloride solution:
In addition, hydrogen is obtained during oil refining.
The production of hydrogen by photolysis of water is one of the most promising methods in the future, however, at the moment, the industrial application of this method is difficult.
Work with the materials of electronic educational resources Laboratory work "Obtaining and properties of hydrogen" and Laboratory work "Reducing properties of hydrogen". Learn the principle of operation of the Kipp apparatus and the Kiryushkin apparatus. Think about in which cases it is more convenient to use the Kipp apparatus, and in which - Kiryushkin. What properties does hydrogen exhibit in reactions?
Oxygen.
The bond in the oxygen molecule is double and very strong. Therefore, oxygen is rather inactive at room temperature. When heated, however, it begins to exhibit strong oxidizing properties.
Oxygen reacts without heating with active metals (alkali, alkaline earth and some lanthanides):
When heated, oxygen reacts with most metals to form oxides:
,
,
.
Silver and less active metals are not oxidized by oxygen.
Oxygen also reacts with most non-metals to form oxides:
,
,
.
Interaction with nitrogen occurs only at very high temperatures, around 2000 °C.
Oxygen does not react with chlorine, bromine and iodine, although many of their oxides can be obtained indirectly.
The interaction of oxygen with fluorine can be carried out by passing an electric discharge through a mixture of gases:
.
Oxygen(II) fluoride is an unstable compound, easily decomposed and a very strong oxidizing agent.
In solutions, oxygen is a strong, albeit slow, oxidizing agent. As a rule, oxygen promotes the transition of metals to higher oxidation states:
The presence of oxygen often makes it possible to dissolve in acids metals located immediately after hydrogen in the voltage series:
When heated, oxygen can oxidize lower metal oxides:
.
Oxygen is not obtained chemically in industry, it is obtained from the air by distillation.
The laboratory uses decomposition reactions of oxygen-rich compounds - nitrates, chlorates, permanganates when heated:
You can also get oxygen by catalytic decomposition of hydrogen peroxide:
In addition, the above water electrolysis reaction can be used to produce oxygen.
Work with the materials of the electronic educational resource Laboratory work "Production of oxygen and its properties."
What is the name of the oxygen collection method used in laboratory work? What other ways of collecting gases are there and which ones are suitable for collecting oxygen?
Task 1. Watch the video clip "Decomposition of potassium permanganate when heated."
Answer the questions:
- Which of the solid products of the reaction is soluble in water?
- What color is potassium permanganate solution?
- What is the color of potassium manganate solution?
Write the equations for the ongoing reactions. Equalize them using the electronic balance method.
Discuss the task with the teacher on or in the video room.
Ozone.
The ozone molecule is triatomic and the bonds in it are less strong than in the oxygen molecule, which leads to a greater chemical activity of ozone: ozone easily oxidizes many substances in solutions or in dry form without heating:
Ozone is able to easily oxidize nitric oxide (IV) to nitric oxide (V), and sulfur oxide (IV) to sulfur oxide (VI) without a catalyst:
Ozone gradually decomposes to form oxygen:
To produce ozone, special devices are used - ozonizers, in which a glow discharge is passed through oxygen.
In the laboratory, to obtain small amounts of ozone, decomposition reactions of peroxo compounds and some higher oxides are sometimes used when heated:
Work with the materials of the electronic educational resource Laboratory work "Obtaining ozone and studying its properties."
Explain why the indigo solution becomes colorless. Write the equations for the reactions that occur when solutions of lead nitrate and sodium sulfide are mixed and when ozonized air is passed through the resulting suspension. Write ionic equations for the ion exchange reaction. For the redox reaction, make an electronic balance.
Discuss the task with the teacher on or in the video room.
Chemical properties of water
For a better understanding of the physical properties of water and its significance, work with the materials of electronic educational resources "Anomalous properties of water" and "Water is the most important liquid on Earth."
Water is of great importance for all living organisms - in fact, many living organisms are made up of more than half water. Water is one of the most versatile solvents (at high temperatures and pressures, its capabilities as a solvent increase significantly). From a chemical point of view, water is hydrogen oxide, while in an aqueous solution it dissociates (albeit to a very small extent) into hydrogen cations and hydroxide anions:
.
Water interacts with many metals. With active (alkaline, alkaline earth and some lanthanides) water reacts without heating:
With less active interaction occurs when heated.
In the periodic system, hydrogen is located in two groups of elements that are absolutely opposite in their properties. This feature makes it completely unique. Hydrogen is not just an element or substance, but also a component of many complex compounds, an organogenic and biogenic element. Therefore, we consider its properties and characteristics in more detail.
The release of combustible gas during the interaction of metals and acids was observed as early as the 16th century, that is, during the formation of chemistry as a science. The famous English scientist Henry Cavendish studied the substance starting in 1766 and gave it the name "combustible air". When burned, this gas produced water. Unfortunately, the scientist's adherence to the theory of phlogiston (hypothetical "hyperfine matter") prevented him from coming to the right conclusions.
The French chemist and naturalist A. Lavoisier, together with the engineer J. Meunier and using special gasometers in 1783, synthesized water, and then analyzed it by decomposing water vapor with red-hot iron. Thus, scientists were able to come to the right conclusions. They found that "combustible air" is not only part of the water, but can also be obtained from it.
In 1787, Lavoisier suggested that the studied gas is a simple substance and, accordingly, is among the primary chemical elements. He called it hydrogene (from the Greek words hydor - water + gennao - I give birth), that is, "giving birth to water."
The Russian name "hydrogen" was proposed in 1824 by the chemist M. Solovyov. The determination of the composition of water marked the end of the "phlogiston theory". 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 its mass was taken as the main unit for comparing atomic masses, obtaining a value equal to 1.
Physical properties
Hydrogen is the lightest of all substances known to science (it is 14.4 times lighter than air), its density is 0.0899 g/l (1 atm, 0 °C). This material melts (solidifies) and boils (liquefies), respectively, at -259.1 ° C and -252.8 ° C (only helium has lower boiling and melting t °).
The critical temperature of hydrogen is extremely low (-240 °C). For this reason, its liquefaction is a rather complicated and costly process. The critical pressure of a substance is 12.8 kgf / cm², and the critical density is 0.0312 g / cm³. Among all gases, hydrogen has the highest thermal conductivity: at 1 atm and 0 ° C, it is 0.174 W / (mxK).
The specific heat capacity of a substance under the same conditions is 14.208 kJ / (kgxK) or 3.394 cal / (gh ° C). This element is slightly soluble in water (about 0.0182 ml / g at 1 atm and 20 ° C), but well - in most metals (Ni, Pt, Pa and others), especially in palladium (about 850 volumes per volume of Pd ).
The latter property is associated with its ability to diffuse, while diffusion through a carbon alloy (for example, steel) can be accompanied by the destruction of the alloy due to the interaction of hydrogen with carbon (this process is called decarbonization). In the liquid state, the substance is very light (density - 0.0708 g / cm³ at t ° \u003d -253 ° C) and fluid (viscosity - 13.8 centigrade under the same conditions).
In many compounds, this element exhibits a +1 valency (oxidation state), similar to sodium and other alkali metals. It is usually considered as an analogue of these metals. Accordingly, he heads the I group of the Mendeleev system. In metal hydrides, the hydrogen ion exhibits a negative charge (the oxidation state is -1), that is, Na + H- has a structure similar to Na + Cl- chloride. In accordance with this and some other facts (the closeness of the physical properties of the element "H" and halogens, the ability to replace it with halogens in organic compounds), Hydrogene is assigned to group VII of the Mendeleev system.
Under normal conditions, molecular hydrogen has low activity, directly combining only with the most active of non-metals (with fluorine and chlorine, with the latter - in the light). In turn, when heated, it interacts with many chemical elements.
Atomic hydrogen has an increased chemical activity (compared to molecular hydrogen). With oxygen, it forms water according to the formula:
Н₂ + ½О₂ = Н₂О,
releasing 285.937 kJ/mol of heat or 68.3174 kcal/mol (25°C, 1 atm). Under normal temperature conditions, the reaction proceeds rather slowly, and at t ° >= 550 ° С, it is uncontrolled. The explosive limits of a mixture of hydrogen + oxygen by volume are 4–94% H₂, and mixtures of hydrogen + air are 4–74% H₂ (a mixture of two volumes of H₂ and one volume of O₂ is called explosive gas).
This element is used to reduce most metals, since it takes oxygen from oxides:
Fe₃O₄ + 4H₂ = 3Fe + 4Н₂О,
CuO + H₂ = Cu + H₂O etc.
With different halogens, hydrogen forms hydrogen halides, for example:
H₂ + Cl₂ = 2HCl.
However, when reacting with fluorine, hydrogen explodes (this also happens in the dark, at -252 ° C), reacts with bromine and chlorine only when heated or illuminated, and with iodine - only when heated. When interacting with nitrogen, ammonia is formed, but only on a catalyst, at elevated pressures and temperatures:
ZN₂ + N₂ = 2NH₃.
When heated, hydrogen actively reacts with sulfur:
H₂ + S = H₂S (hydrogen sulfide),
and much more difficult - with tellurium or selenium. Hydrogen reacts with pure carbon without a catalyst, but at high temperatures:
2H₂ + C (amorphous) = CH₄ (methane).
This substance directly reacts with some of the metals (alkali, alkaline earth and others), forming hydrides, for example:
Н₂ + 2Li = 2LiH.
Of no small practical importance are the interactions of hydrogen and carbon monoxide (II). In this case, depending on the pressure, temperature and catalyst, various organic compounds are formed: HCHO, CH₃OH, etc. Unsaturated hydrocarbons turn into saturated ones during the reaction, for example:
С n Н₂ n + Н₂ = С n Н₂ n ₊₂.
Hydrogen and its compounds play an exceptional role in chemistry. It determines the acidic properties of the so-called. protic acids tend to form hydrogen bonds with different elements, which have a significant effect on the properties of many inorganic and organic compounds.
Getting hydrogen
The main types of raw materials for the industrial production of this element are refinery gases, natural combustible and coke oven gases. It is also obtained from water through electrolysis (in places with affordable electricity). One of the most important methods for producing material from natural gas is the catalytic interaction of hydrocarbons, mainly methane, with water vapor (the so-called conversion). For example:
CH₄ + H₂O = CO + ZH₂.
Incomplete oxidation of hydrocarbons with oxygen:
CH₄ + ½O₂ \u003d CO + 2H₂.
Synthesized carbon monoxide (II) undergoes conversion:
CO + H₂O = CO₂ + H₂.
Hydrogen produced from natural gas is the cheapest.
For electrolysis of water, direct current is used, which is passed through a solution of NaOH or KOH (acids are not used to avoid corrosion of the equipment). Under laboratory conditions, the material is obtained by electrolysis of water or as a result of the reaction between hydrochloric acid and zinc. However, more often used ready-made factory material in cylinders.
From refinery gases and coke oven gas, this element is isolated by removing all other components of the gas mixture, since they are more easily liquefied during deep cooling.
This material began to be obtained industrially at the end of the 18th century. Then it was used to fill balloons. At the moment, hydrogen is widely used in industry, mainly in the chemical industry, for the production of ammonia.
Mass consumers of the substance are manufacturers of methyl and other alcohols, synthetic gasoline and many other products. They are obtained by synthesis from carbon monoxide (II) and hydrogen. Hydrogene is used for the hydrogenation of heavy and solid liquid fuels, fats, etc., for the synthesis of HCl, hydrotreating of petroleum products, as well as in cutting / welding of metals. The most important elements for nuclear energy are its isotopes - tritium and deuterium.
The biological role of hydrogen
About 10% of the mass of living organisms (on average) falls on this element. It is part of water and the most important groups of natural compounds, including proteins, nucleic acids, lipids, carbohydrates. What does it serve?
This material plays a decisive role: in maintaining the spatial structure of proteins (quaternary), in implementing the principle of complementarity of nucleic acids (i.e., in the implementation and storage of genetic information), in general, in “recognition” at the molecular level.
The hydrogen ion H+ takes part in important dynamic reactions/processes in the body. Including: in biological oxidation, which provides living cells with energy, in biosynthesis reactions, in photosynthesis in plants, in bacterial photosynthesis and nitrogen fixation, in maintaining acid-base balance and homeostasis, in membrane transport processes. Along with carbon and oxygen, it forms the functional and structural basis of the phenomena of life.
10.1 Hydrogen
The name "hydrogen" refers to both a chemical element and a simple substance. Element hydrogen is made up of hydrogen atoms. simple substance hydrogen is made up of hydrogen molecules.
a) Chemical element hydrogen
In the natural series of elements, the serial number of hydrogen is 1. In the system of elements, hydrogen is in the first period in the IA or VIIA group.
Hydrogen is one of the most abundant elements on Earth. The molar fraction of hydrogen atoms in the atmosphere, hydrosphere and lithosphere of the Earth (collectively, this is called the earth's crust) is 0.17. It is found in water, many minerals, oil, natural gas, plants and animals. The average human body contains about 7 kilograms of hydrogen.
There are three isotopes of hydrogen:
a) light hydrogen - protium,
b) heavy hydrogen - deuterium(D)
c) superheavy hydrogen - tritium(T).
Tritium is an unstable (radioactive) isotope, so it practically does not occur in nature. Deuterium is stable, but there is very little of it: w D = 0.015% (of the mass of all terrestrial hydrogen). Therefore, the atomic mass of hydrogen differs very little from 1 Dn (1.00794 Dn).
b) Hydrogen atom
From the previous sections of the chemistry course, you already know the following characteristics of the hydrogen atom:
The valence capabilities of a hydrogen atom are determined by the presence of one electron in a single valence orbital. A large ionization energy makes the hydrogen atom not prone to donate an electron, and not too high an electron affinity leads to a slight tendency to accept it. Consequently, in chemical systems, the formation of the H cation is impossible, and compounds with the H anion are not very stable. Thus, the formation of a covalent bond with other atoms due to its one unpaired electron is most characteristic of the hydrogen atom. Both in the case of the formation of an anion and in the case of the formation of a covalent bond, the hydrogen atom is monovalent.
In a simple substance, the oxidation state of hydrogen atoms is zero, in most compounds hydrogen exhibits an oxidation state of +I, and only in hydrides of the least electronegative elements in hydrogen is an oxidation state of –I.
Information about the valence capabilities of the hydrogen atom is given in table 28. The valence state of a hydrogen atom connected by one covalent bond with any atom is indicated in the table by the symbol "H-".
Table 28Valence possibilities of the hydrogen atom
Valence state |
Examples of chemicals |
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I |
HCl, H 2 O, H 2 S, NH 3 , CH 4 , C 2 H 6 , NH 4 Cl, H 2 SO 4 , NaHCO 3 , KOH |
|||
NaH, KH, CaH 2 , BaH 2 |
c) Hydrogen molecule
The diatomic hydrogen molecule H 2 is formed when hydrogen atoms are bound by the only covalent bond possible for them. Communication is formed by the exchange mechanism. According to the way electron clouds overlap, this is an s-bond (Fig. 10.1 A). Since the atoms are the same, the bond is non-polar.
Interatomic distance (more precisely, the equilibrium interatomic distance, because atoms vibrate) in a hydrogen molecule r(H-H) = 0.74 A (Fig. 10.1 V), which is much less than the sum of orbital radii (1.06 A). Consequently, the electron clouds of bonding atoms overlap deeply (Fig. 10.1 b), and the bond in the hydrogen molecule is strong. This is also evidenced by the rather large value of the binding energy (454 kJ/mol).
If we characterize the shape of the molecule by the boundary surface (similar to the boundary surface of the electron cloud), then we can say that the hydrogen molecule has the shape of a slightly deformed (elongated) ball (Fig. 10.1 G).
d) Hydrogen (substance)
Under normal conditions, hydrogen is a colorless and odorless gas. In small quantities, it is non-toxic. Solid hydrogen melts at 14 K (–259°C), while liquid hydrogen boils at 20 K (–253°C). Low melting and boiling points, a very small temperature interval for the existence of liquid hydrogen (only 6 °C), as well as small molar heats of melting (0.117 kJ/mol) and vaporization (0.903 kJ/mol) indicate that intermolecular bonds in hydrogen very weak.
Hydrogen density r (H 2) \u003d (2 g / mol): (22.4 l / mol) \u003d 0.0893 g / l. For comparison: the average air density is 1.29 g/l. That is, hydrogen is 14.5 times "lighter" than air. It is practically insoluble in water.
At room temperature, hydrogen is inactive, but when heated, it reacts with many substances. In these reactions, hydrogen atoms can both increase and decrease their oxidation state: H 2 + 2 e- \u003d 2H -I, H 2 - 2 e- \u003d 2H + I.
In the first case, hydrogen is an oxidizing agent, for example, in reactions with sodium or calcium: 2Na + H 2 = 2NaH, ( t) Ca + H 2 = CaH 2 . ( t)
But the reducing properties are more characteristic of hydrogen: O 2 + 2H 2 \u003d 2H 2 O, ( t)
CuO + H 2 \u003d Cu + H 2 O. ( t)
When heated, hydrogen is oxidized not only by oxygen, but also by some other non-metals, such as fluorine, chlorine, sulfur, and even nitrogen.
In the laboratory, hydrogen is produced by the reaction
Zn + H 2 SO 4 \u003d ZnSO 4 + H 2.
Iron, aluminum and some other metals can be used instead of zinc, and some other dilute acids can be used instead of sulfuric acid. The resulting hydrogen is collected in a test tube by the method of water displacement (see Fig. 10.2 b) or simply into an inverted flask (Fig. 10.2 A).
In industry, hydrogen is obtained in large quantities from natural gas (mainly methane) by interacting with water vapor at 800 °C in the presence of a nickel catalyst:
CH 4 + 2H 2 O \u003d 4H 2 + CO 2 ( t, Ni)
or treated at high temperature with water vapor coal:
2H 2 O + C \u003d 2H 2 + CO 2. ( t)
Pure hydrogen is obtained from water by decomposing it with an electric current (subjecting to electrolysis):
2H 2 O \u003d 2H 2 + O 2 (electrolysis).
e) Hydrogen compounds
Hydrides (binary compounds containing hydrogen) are divided into two main types:
a) volatile
(molecular) hydrides,
b) salt-like (ionic) hydrides.
Elements IVA - VIIA groups and boron form molecular hydrides. Of these, only hydrides of elements that form non-metals are stable:
B 2 H 6 ; CH 4 ; NH3; H2O; HF
SiH 4 ;PH 3 ; H2S; HCl
AsH 3 ; H2Se; HBr
H2Te; HI
With the exception of water, all of these compounds are gaseous substances at room temperature, hence their name - "volatile hydrides".
Some of the elements that form non-metals are also included in more complex hydrides. For example, carbon forms compounds with the general formulas C n H2 n+2 , C n H2 n, C n H2 n-2 and others, where n can be very large (organic chemistry studies these compounds).
Ionic hydrides include alkali, alkaline earth and magnesium hydrides. The crystals of these hydrides consist of H anions and metal cations in the highest oxidation state of Me or Me 2 (depending on the group of the system of elements).
| LiH | |
| NaH | MgH2 |
| KH | CaH2 |
| RbH | SrH 2 |
| CSH | BaH2 |
Both ionic and almost all molecular hydrides (except H 2 O and HF) are reducing agents, but ionic hydrides exhibit reducing properties much stronger than molecular ones.
In addition to hydrides, hydrogen is a part of hydroxides and some salts. You will get acquainted with the properties of these more complex hydrogen compounds in the following chapters.
The main consumers of hydrogen produced in industry are plants for the production of ammonia and nitrogen fertilizers, where ammonia is obtained directly from nitrogen and hydrogen:
N 2 + 3H 2 2NH 3 ( R, t, Pt is the catalyst).
Hydrogen is used in large quantities to produce methyl alcohol (methanol) by the reaction 2H 2 + CO = CH 3 OH ( t, ZnO - catalyst), as well as in the production of hydrogen chloride, which is obtained directly from chlorine and hydrogen:
H 2 + Cl 2 \u003d 2HCl.
Sometimes hydrogen is used in metallurgy as a reducing agent in the production of pure metals, for example: Fe 2 O 3 + 3H 2 = 2Fe + 3H 2 O.
1. What particles do the nuclei of a) protium, b) deuterium, c) tritium consist of?
2. Compare the ionization energy of a hydrogen atom with the ionization energy of atoms of other elements. Which element is closest to hydrogen in this characteristic?
3. Do the same for the electron affinity energy
4. Compare the direction of polarization of the covalent bond and the degree of oxidation of hydrogen in the compounds: a) BeH 2 , CH 4 , NH 3 , H 2 O, HF; b) CH 4, SiH 4, GeH 4.
5. Write down the simplest, molecular, structural and spatial formula of hydrogen. Which one is the most commonly used?
6. They often say: "Hydrogen is lighter than air." What is meant by this? In what cases can this expression be taken literally, and in what cases not?
7. Make the structural formulas of potassium and calcium hydrides, as well as ammonia, hydrogen sulfide and hydrogen bromide.
8. Knowing the molar heats of fusion and vaporization of hydrogen, determine the values of the corresponding specific quantities.
9. For each of the four reactions illustrating the basic chemical properties of hydrogen, make an electronic balance. List the oxidizing and reducing agents.
10. Determine the mass of zinc required to obtain 4.48 liters of hydrogen in a laboratory way.
11. Determine the mass and volume of hydrogen that can be obtained from 30 m 3 of a mixture of methane and water vapor, taken in a volume ratio of 1: 2, with a yield of 80%.
12. Make up the equations of the reactions that take place during the interaction of hydrogen a) with fluorine, b) with sulfur.
13. The reaction schemes below illustrate the basic chemical properties of ionic hydrides:
a) MH + O 2 MOH ( t); b) MH + Cl 2 MCl + HCl ( t);
c) MH + H 2 O MOH + H 2; d) MH + HCl(p) MCl + H 2
Here M is lithium, sodium, potassium, rubidium or cesium. Make up the equations of the corresponding reactions if M is sodium. Illustrate the chemical properties of calcium hydride with reaction equations.
14. Using the electron balance method, write the equations for the following reactions illustrating the reducing properties of some molecular hydrides:
a) HI + Cl 2 HCl + I 2 ( t); b) NH 3 + O 2 H 2 O + N 2 ( t); c) CH 4 + O 2 H 2 O + CO 2 ( t).
10.2 Oxygen
As in the case of hydrogen, the word "oxygen" is the name of both a chemical element and a simple substance. Except simple substance" oxygen"(dioxygen) the chemical element oxygen forms another simple substance called " ozone"(trioxygen). These are allotropic modifications of oxygen. The substance oxygen consists of oxygen molecules O 2 , and the substance ozone consists of ozone molecules O 3 .
a) The chemical element oxygen
In the natural series of elements, the serial number of oxygen is 8. In the system of elements, oxygen is in the second period in the VIA group.
Oxygen is the most abundant element on Earth. In the earth's crust, every second atom is an oxygen atom, that is, the molar fraction of oxygen in the atmosphere, hydrosphere and lithosphere of the Earth is about 50%. Oxygen (substance) is an integral part of air. The volume fraction of oxygen in the air is 21%. Oxygen (element) is a part of water, many minerals, as well as plants and animals. The human body contains an average of 43 kg of oxygen.
Natural oxygen consists of three isotopes (16 O, 17 O and 18 O), of which the lightest isotope 16 O is the most common. Therefore, the atomic mass of oxygen is close to 16 Dn (15.9994 Dn).
b) Oxygen atom
You know the following characteristics of the oxygen atom.
Table 29Valence possibilities of the oxygen atom
Valence state |
Examples of chemicals |
|||
Al 2 O 3 , Fe 2 O 3 , Cr 2 O 3 * |
||||
-II |
H 2 O, SO 2, SO 3, CO 2, SiO 2, H 2 SO 4, HNO 2, HClO 4, COCl 2, H 2 O 2 |
|||
NaOH, KOH, Ca(OH) 2 , Ba(OH) 2 |
||||
Li 2 O, Na 2 O, MgO, CaO, BaO, FeO, La 2 O 3 |
* These oxides can also be considered as ionic compounds.
** The oxygen atoms in the molecule are not in the given valence state; this is just an example of a substance with an oxidation state of oxygen atoms equal to zero
A large ionization energy (like that of hydrogen) excludes the formation of a simple cation from the oxygen atom. The electron affinity energy is quite high (almost twice as high as that of hydrogen), which provides a greater propensity for the oxygen atom to attach electrons and the ability to form O 2A anions. But the electron affinity energy of the oxygen atom is still less than that of halogen atoms and even other elements of the VIA group. Therefore, oxygen anions ( oxide ions) exist only in compounds of oxygen with elements whose atoms donate electrons very easily.
By sharing two unpaired electrons, an oxygen atom can form two covalent bonds. Two lone pairs of electrons, due to the impossibility of excitation, can only enter into a donor-acceptor interaction. Thus, without taking into account the multiplicity of bonds and hybridization, the oxygen atom can be in one of the five valence states (Table 29).
The most characteristic of the oxygen atom is the valence state with W k \u003d 2, that is, the formation of two covalent bonds due to two unpaired electrons.
The very high electronegativity of the oxygen atom (only fluorine is higher) leads to the fact that in most of its compounds, oxygen has an oxidation state of -II. There are substances in which oxygen exhibits other values of the oxidation state, some of them are given in table 29 as examples, and the comparative stability is shown in fig. 10.3.
c) Oxygen molecule
It has been experimentally established that the diatomic oxygen molecule O 2 contains two unpaired electrons. Using the method of valence bonds, such an electronic structure of this molecule cannot be explained. Nevertheless, the bond in the oxygen molecule is close in properties to the covalent bond. The oxygen molecule is non-polar. Interatomic distance ( r o–o = 1.21 A = 121 nm) is less than the distance between atoms connected by a single bond. The molar binding energy is rather high and amounts to 498 kJ/mol.
d) Oxygen (substance)
Under normal conditions, oxygen is a colorless and odorless gas. Solid oxygen melts at 55 K (–218 °C), while liquid oxygen boils at 90 K (–183 °C).
Intermolecular bonds in solid and liquid oxygen are somewhat stronger than in hydrogen, as evidenced by the larger temperature interval for the existence of liquid oxygen (36 ° C) and the molar heats of melting (0.446 kJ / mol) and vaporization (6. 83 kJ/mol).
Oxygen is slightly soluble in water: at 0 ° C, only 5 volumes of oxygen (gas!) dissolve in 100 volumes of water (liquid!)
The high propensity of oxygen atoms to attach electrons and high electronegativity lead to the fact that oxygen exhibits only oxidizing properties. These properties are especially pronounced at high temperatures.
Oxygen reacts with many metals: 2Ca + O 2 = 2CaO, 3Fe + 2O 2 = Fe 3 O 4 ( t);
non-metals: C + O 2 \u003d CO 2, P 4 + 5O 2 \u003d P 4 O 10,
and complex substances: CH 4 + 2O 2 \u003d CO 2 + 2H 2 O, 2H 2 S + 3O 2 \u003d 2H 2 O + 2SO 2.
Most often, as a result of such reactions, various oxides are obtained (see Ch. II § 5), but active alkali metals, such as sodium, when burned, turn into peroxides:
2Na + O 2 \u003d Na 2 O 2.
Structural formula of the resulting sodium peroxide (Na) 2 (O-O).
A smoldering splinter placed in oxygen flares up. This is a convenient and easy way to detect pure oxygen.
In industry, oxygen is obtained from air by rectification (complex distillation), and in the laboratory, by subjecting some oxygen-containing compounds to thermal decomposition, for example:
2KMnO 4 \u003d K 2 MnO 4 + MnO 2 + O 2 (200 ° C);
2KClO 3 \u003d 2KCl + 3O 2 (150 ° C, MnO 2 - catalyst);
2KNO 3 \u003d 2KNO 2 + 3O 2 (400 ° C)
and, in addition, by catalytic decomposition of hydrogen peroxide at room temperature: 2H 2 O 2 = 2H 2 O + O 2 (MnO 2 -catalyst).
Pure oxygen is used in industry to intensify those processes in which oxidation occurs and to create a high-temperature flame. In rocket technology, liquid oxygen is used as an oxidizing agent.
Oxygen plays an important role in maintaining the life of plants, animals and humans. Under normal conditions, a person needs enough oxygen to breathe in the air. But in conditions where there is not enough air, or it is not available at all (in airplanes, during diving operations, in space ships, etc.), special gas mixtures containing oxygen are prepared for breathing. Oxygen is also used in medicine for diseases that cause difficulty in breathing.
e) Ozone and its molecules
Ozone O 3 is the second allotropic modification of oxygen.
The triatomic ozone molecule has a corner structure midway between the two structures represented by the following formulas:
Ozone is a dark blue gas with a pungent odor. Due to its strong oxidative activity, it is poisonous. Ozone is one and a half times "heavier" than oxygen and somewhat more than oxygen, soluble in water.
Ozone is formed in the atmosphere from oxygen during lightning electrical discharges:
3O 2 \u003d 2O 3 ().
At ordinary temperatures, ozone slowly turns into oxygen, and when heated, this process proceeds with an explosion.
Ozone is contained in the so-called "ozone layer" of the earth's atmosphere, protecting all life on Earth from the harmful effects of solar radiation.
In some cities, ozone is used instead of chlorine to disinfect (decontaminate) drinking water.
Draw the structural formulas of the following substances: OF 2 , H 2 O, H 2 O 2 , H 3 PO 4 , (H 3 O) 2 SO 4 , BaO, BaO 2 , Ba(OH) 2 . Name these substances. Describe the valence states of the oxygen atoms in these compounds.
Determine the valency and oxidation state of each of the oxygen atoms.
2. Make the equations for the reactions of combustion in oxygen of lithium, magnesium, aluminum, silicon, red phosphorus and selenium (the atoms of selenium are oxidized to the oxidation state + IV, the atoms of the remaining elements to the highest oxidation state). What classes of oxides do the products of these reactions belong to?
3. How many liters of ozone can be obtained (under normal conditions) a) from 9 liters of oxygen, b) from 8 g of oxygen?
Water is the most abundant substance in the earth's crust. The mass of earth's water is estimated at 10 18 tons. Water is the basis of the hydrosphere of our planet, in addition, it is contained in the atmosphere, in the form of ice it forms the polar caps of the Earth and high-mountain glaciers, and is also part of various rocks. The mass fraction of water in the human body is about 70%.
Water is the only substance that has its own special names in all three states of aggregation.
The electronic structure of the water molecule (Fig. 10.4 A) we have studied in detail earlier (see § 7.10).
Due to the polarity of the O–H bonds and the angular shape, the water molecule is electric dipole.
To characterize the polarity of an electric dipole, a physical quantity called " electric moment of an electric dipole or simply " dipole moment".
In chemistry, the dipole moment is measured in debyes: 1 D = 3.34. 10–30 C. m
In a water molecule there are two polar covalent bonds, that is, two electric dipoles, each of which has its own dipole moment (and). The total dipole moment of a molecule is equal to the vector sum of these two moments (Fig. 10.5):
(H 2 O) = 
,
Where q 1 and q 2 - partial charges (+) on hydrogen atoms, and and - interatomic distances O - H in the molecule. Because q 1 = q 2 = q, a , then
The experimentally determined dipole moments of the water molecule and some other molecules are given in the table.
Table 30Dipole moments of some polar molecules
Molecule |
Molecule |
Molecule |
|||
Given the dipole nature of the water molecule, it is often schematically depicted as follows:
Pure water is a colorless liquid without taste or smell. Some basic physical characteristics of water are given in the table.
Table 31Some physical characteristics of water
The large values of the molar heats of melting and vaporization (an order of magnitude greater than those of hydrogen and oxygen) indicate that water molecules, both in solid and liquid substances, are quite strongly bonded to each other. These connections are called hydrogen bonds".
ELECTRIC DIPOLE, DIPOLE MOMENT, COMMUNICATION POLARITY, MOLECULE POLARITY.
How many valence electrons of an oxygen atom take part in the formation of bonds in a water molecule?
2. When overlapping which orbitals, bonds are formed between hydrogen and oxygen in a water molecule?
3. Make a diagram of the formation of bonds in a molecule of hydrogen peroxide H 2 O 2. What can you say about the spatial structure of this molecule?
4. Interatomic distances in HF, HCl and HBr molecules are equal, respectively, to 0.92; 1.28 and 1.41. Using the table of dipole moments, calculate and compare the partial charges on the hydrogen atoms in these molecules.
5. Interatomic distances S - H in a hydrogen sulfide molecule are equal to 1.34, and the angle between bonds is 92 °. Determine the values of partial charges on sulfur and hydrogen atoms. What can you say about the hybridization of the valence orbitals of the sulfur atom?
10.4. hydrogen bond
As you already know, due to the significant difference in the electronegativity of hydrogen and oxygen (2.10 and 3.50), a large positive partial charge arises on the hydrogen atom in the water molecule ( q h = 0.33 e), while the oxygen atom has an even larger negative partial charge ( q h = -0.66 e). Recall also that the oxygen atom has two lone pairs of electrons per sp 3-hybrid AO. The hydrogen atom of one water molecule is attracted to the oxygen atom of another molecule, and, in addition, the half-empty 1s-AO of the hydrogen atom partially accepts a pair of electrons from the oxygen atom. As a result of these interactions between molecules, a special type of intermolecular bonds arises - a hydrogen bond.
In the case of water, hydrogen bond formation can be schematically represented as follows:
In the last structural formula, three dots (dashed stroke, not electrons!) Show a hydrogen bond.
Hydrogen bonding exists not only between water molecules. It is formed if two conditions are met:
1) there is a strongly polar H–E bond in the molecule (E is the symbol of an atom of a sufficiently electronegative element),
2) in the molecule there is an atom E with a large negative partial charge and an unshared pair of electrons.
As element E can be fluorine, oxygen and nitrogen. Hydrogen bonds are much weaker if E is chlorine or sulfur.
Examples of substances with a hydrogen bond between molecules: hydrogen fluoride, solid or liquid ammonia, ethyl alcohol and many others.
In liquid hydrogen fluoride, its molecules are linked by hydrogen bonds into rather long chains, while in liquid and solid ammonia, three-dimensional networks are formed.
In terms of strength, a hydrogen bond is intermediate between a chemical bond and other types of intermolecular bonds. The molar energy of the hydrogen bond usually lies in the range from 5 to 50 kJ/mol.
In solid water (that is, ice crystals), all hydrogen atoms are hydrogen bonded to oxygen atoms, with each oxygen atom forming two hydrogen bonds (using both lone pairs of electrons). Such a structure makes ice more "loose" compared to liquid water, where some of the hydrogen bonds are broken, and the molecules get the opportunity to "pack" somewhat more densely. This feature of the structure of ice explains why, unlike most other substances, water in the solid state has a lower density than in the liquid state. Water reaches its maximum density at 4 ° C - at this temperature, quite a lot of hydrogen bonds are broken, and thermal expansion does not yet have a very strong effect on density.
Hydrogen bonds are very important in our life. Imagine for a moment that hydrogen bonds have ceased to form. Here are some consequences:
- water at room temperature would become gaseous as its boiling point would drop to about -80°C;
- all reservoirs would begin to freeze from the bottom, since the density of ice would be greater than the density of liquid water;
- the DNA double helix would cease to exist, and much more.
The examples given are enough to understand that in this case, nature on our planet would be completely different.
HYDROGEN BOND, CONDITIONS OF ITS FORMATION.
The formula of ethyl alcohol is CH 3 -CH 2 -O-H. Between what atoms of different molecules of this substance are hydrogen bonds formed? Make structural formulas illustrating their formation.
2. Hydrogen bonds exist not only in individual substances, but also in solutions. Show using structural formulas how hydrogen bonds are formed in an aqueous solution of a) ammonia, b) hydrogen fluoride, c) ethanol (ethyl alcohol). \u003d 2H 2 O.
Both of these reactions proceed in water constantly and at the same rate, therefore, there is an equilibrium in water: 2H 2 O AN 3 O + OH.
This balance is called autoprotolysis equilibrium water.
The direct reaction of this reversible process is endothermic, therefore, when heated, autoprotolysis increases, while at room temperature, the equilibrium is shifted to the left, that is, the concentrations of H 3 O and OH ions are negligible. What are they equal to?
According to the law of mass action
But due to the fact that the number of reacted water molecules is insignificant compared to the total number of water molecules, we can assume that the water concentration during autoprotolysis remains practically unchanged, and 2 = const Such a low concentration of oppositely charged ions in pure water explains why this liquid, although poorly, still conducts electric current.
AUTOPROTOLYSIS OF WATER, AUTOPROTOLYSIS CONSTANT (IONIC PRODUCT) OF WATER.
The ionic product of liquid ammonia (boiling point -33 ° C) is 2 10 -28. Write an equation for the autoprotolysis of ammonia. Determine the concentration of ammonium ions in pure liquid ammonia. The electrical conductivity of which of the substances is greater, water or liquid ammonia?
1. Obtaining hydrogen and its combustion (reducing properties).
2. Obtaining oxygen and combustion of substances in it (oxidizing properties).
General and inorganic chemistry
Lecture 6. Hydrogen and oxygen. Water. Hydrogen peroxide.
Hydrogen
The hydrogen atom is the simplest object of chemistry. Strictly speaking, its ion - the proton - is even simpler. First described in 1766 by Cavendish. Name from Greek. "hydro genes" - generating water.
The radius of a hydrogen atom is approximately 0.5 * 10-10 m, and its ion (proton) is 1.2 * 10-15 m. Or from 50 pm to 1.2 * 10-3 pm or from 50 meters (SCA diagonal ) up to 1 mm.
The next 1s element, lithium, only changes from 155 pm to 68 pm for Li+. Such a difference in the size of an atom and its cation (5 orders of magnitude) is unique.
Due to the small size of the proton, the exchange hydrogen bond, primarily between oxygen, nitrogen and fluorine atoms. The strength of hydrogen bonds is 10–40 kJ/mol, which is much less than the breaking energy of most ordinary bonds (100–150 kJ/mol in organic molecules), but more than the average kinetic energy of thermal motion at 370 C (4 kJ/mol). As a result, in a living organism, hydrogen bonds are reversibly broken, ensuring the flow of vital processes.
Hydrogen melts at 14 K, boils at 20.3 K (pressure 1 atm), the density of liquid hydrogen is only 71 g/l (14 times lighter than water).
In the rarefied interstellar medium, excited hydrogen atoms were found with transitions up to n 733 → 732 with a wavelength of 18 m, which corresponds to a Bohr radius (r = n2 * 0.5 * 10-10 m) of the order of 0.1 mm (!).
The most common element in space (88.6% of atoms, 11.3% of atoms are helium, and only 0.1% are atoms of all other elements).
4 H → 4 He + 26.7 MeV 1 eV = 96.48 kJ/mol
Since protons have spin 1/2, there are three types of hydrogen molecules:
orthohydrogen o-H2 with parallel nuclear spins, parahydrogen n-H2 with antiparallel spins and normal n-H2 - a mixture of 75% ortho-hydrogen and 25% para-hydrogen. During the transformation of o-H2 → p-H2, 1418 J/mol is released.
Properties of ortho- and parahydrogen
Since the atomic mass of hydrogen is the minimum possible, its isotopes - deuterium D (2 H) and tritium T (3 H) differ significantly from protium 1 H in physical and chemical properties. For example, the replacement of one of the hydrogens in an organic compound with deuterium significantly affects its vibrational (infrared) spectrum, which makes it possible to establish the structure of complex molecules. Similar substitutions (“labeled atom method”) are also used to establish the mechanisms of complex
chemical and biochemical processes. The method of labeled atoms is especially sensitive when radioactive tritium is used instead of protium (β-decay, half-life 12.5 years).
Properties of protium and deuterium
Density, g/l (20 K) |
|||||||
Main method hydrogen production in industry – methane conversion |
|||||||
or coal hydration at 800-11000 C (catalyst): |
|||||||
CH4 + H2 O = CO + 3 H2 |
above 10000 С |
||||||
"Water gas": C + H2 O = CO + H2 |
|||||||
Then CO conversion: CO + H2 O = CO2 + H2 |
4000 C, cobalt oxides |
||||||
Total: C + 2 H2 O = CO2 + 2 H2
Other sources of hydrogen.
Coke oven gas: about 55% hydrogen, 25% methane, up to 2% heavy hydrocarbons, 4-6% CO, 2% CO2, 10-12% nitrogen.
Hydrogen as a combustion product:
Si + Ca(OH)2 + 2 NaOH = Na2 SiO3 + CaO + 2 H2
Up to 370 liters of hydrogen are released per 1 kg of pyrotechnic mixture.
Hydrogen in the form of a simple substance is used for the production of ammonia and hydrogenation (hardening) of vegetable fats, for the reduction from oxides of certain metals (molybdenum, tungsten), for the production of hydrides (LiH, CaH2,
LiAlH4).
The enthalpy of the reaction: H. + H. = H2 is -436 kJ / mol, so atomic hydrogen is used to produce a high-temperature reducing "flame" ("Langmuir burner"). A jet of hydrogen in an electric arc is atomized at 35,000 C by 30%, then, with the recombination of atoms, it is possible to reach 50,000 C.
Liquefied hydrogen is used as fuel in rockets (see oxygen). Promising environmentally friendly fuel for land transport; experiments are underway on the use of hydrogen metal hydride batteries. For example, the LaNi5 alloy can absorb 1.5-2 times more hydrogen than is contained in the same volume (as the volume of the alloy) of liquid hydrogen.
Oxygen
According to now generally accepted data, oxygen was discovered in 1774 by J. Priestley and independently by K. Scheele. The history of the discovery of oxygen is a good example of the influence of paradigms on the development of science (see Appendix 1).
Apparently, in fact, oxygen was discovered much earlier than the official date. In 1620, anyone could ride along the Thames (in the Thames) in a submarine designed by Cornelius van Drebbel. The boat moved under water thanks to the efforts of a dozen rowers. According to numerous eyewitnesses, the inventor of the submarine successfully solved the problem of breathing by “refreshing” the air in it by chemical means. Robert Boyle wrote in 1661: “... In addition to the mechanical construction of the boat, the inventor had a chemical solution (liquor), which he
considered the main secret of scuba diving. And when from time to time he became convinced that the breathable part of the air had already been used up and made it difficult for people in the boat to breathe, he could, by opening a vessel filled with this solution, quickly replenish the air with such a content of vital parts that would make it again suitable for breath for a sufficiently long time.
A healthy person in a calm state per day pumps about 7200 liters of air through his lungs, taking 720 liters of oxygen irrevocably. In a closed room with a volume of 6 m3, a person can survive without ventilation for up to 12 hours, and during physical work 3-4 hours. The main cause of difficulty breathing is not a lack of oxygen, but accumulation of carbon dioxide from 0.3 to 2.5%.
For a long time, the main method of obtaining oxygen was the "barium" cycle (obtaining oxygen using the Brin method):
BaSO4 -t-→ BaO + SO3;
5000C ->
BaO + 0.5 O2 ====== BaO2<- 7000 C
Drebbel's secret solution could be a solution of hydrogen peroxide: BaO2 + H2 SO4 = BaSO4 ↓ + H2 O2
Obtaining oxygen during combustion of the pyromixture: NaClO3 = NaCl + 1.5 O2 + 50.5 kJ
In a mixture of up to 80% NaClO3, up to 10% iron powder, 4% barium peroxide and glass wool.
The oxygen molecule is paramagnetic (practically a biradical), therefore its activity is high. Organic substances are oxidized in air through the stage of peroxide formation.
Oxygen melts at 54.8 K and boils at 90.2 K.
The allotropic modification of the element oxygen is the substance ozone O3. The biological ozone protection of the Earth is extremely important. At an altitude of 20-25 km, an equilibrium is established:
UV<280 нм |
UV 280-320nm |
||
O2 ----> 2 O* |
O* + O2 + M --> O3 |
O3------- |
> O2 + O |
(M - N2 , Ar) |
|||
In 1974, it was discovered that atomic chlorine, which is formed from freons at an altitude of more than 25 km, catalyzes the decay of ozone, as if replacing the "ozone" ultraviolet. This UV is capable of causing skin cancer (up to 600,000 cases per year in the US). The ban on freons in aerosol cans has been in effect in the United States since 1978.
Since 1990, the list of prohibited substances (in 92 countries) has included CH3 CCl3, CCl4, chlorobromohydrocarbons - their production is curtailed by 2000.
Combustion of hydrogen in oxygen
The reaction is very complex (scheme in lecture 3), so a long study was required before the start of practical application.
July 21, 1969 the first earthling - N. Armstrong walked on the moon. The Saturn-5 launch vehicle (designed by Wernher von Braun) consists of three stages. In the first, kerosene and oxygen, in the second and third - liquid hydrogen and oxygen. Total 468 tons of liquid O2 and H2. 13 successful launches were made.
Since April 1981, the Space Shuttle has been operating in the USA: 713 tons of liquid O2 and H2, as well as two solid-propellant boosters of 590 tons each (the total mass of solid fuel is 987 tons). The first 40 km ascent to the TTU, from 40 to 113 km engines run on hydrogen and oxygen.
On May 15, 1987, the first launch of Energia, on November 15, 1988, the first and only flight of Buran. The launch weight is 2400 tons, the mass of fuel (kerosene in
side compartments, liquid O2 and H2) 2000 tons. Engine power 125000 MW, payload 105 tons.
The combustion was not always controlled and successful.
In 1936, the world's largest hydrogen airship LZ-129 "Hindenburg" was built. The volume is 200,000 m3, the length is about 250 m, the diameter is 41.2 m. The speed is 135 km / h thanks to 4 engines of 1100 hp each, the payload is 88 tons. The airship made 37 flights across the Atlantic and transported more than 3 thousand passengers.
On May 6, 1937, while mooring in the USA, the airship exploded and burned down. One possible reason is sabotage.
On January 28, 1986, at the 74th second of the flight, the Challenger exploded with seven cosmonauts - the 25th flight of the Shuttle system. The reason is a defect in the solid propellant booster.
Demonstration:
explosive gas explosion (a mixture of hydrogen and oxygen)
fuel cells
A technically important variant of this combustion reaction is the division of the process into two:
hydrogen electrooxidation (anode): 2 H2 + 4 OH– - 4 e– = 4 H2 O
oxygen electroreduction (cathode): O2 + 2 H2 O + 4 e– = 4 OH–
The system in which such “burning” is carried out is fuel cell. The efficiency is much higher than that of thermal power plants, since there is no
special stage of heat generation. Maximum efficiency = ∆G/∆H; for the combustion of hydrogen, 94% is obtained.
The effect has been known since 1839, but the first practically working fuel cells have been implemented
at the end of the 20th century in space (“Gemini”, “Apollo”, “Shuttle” - USA, “Buran” - USSR).
Fuel Cell Perspectives [17]
A representative of Ballard Power Systems, speaking at a scientific conference in Washington, emphasized that a fuel cell engine will become commercially viable when it meets four main criteria: lower cost of generated energy, increased durability, reduced installation size and the ability to start quickly in cold weather. . The cost of one kilowatt of energy generated by a fuel cell plant should be reduced to $30. For comparison, in 2004 the same figure was $103, and in 2005 it is expected to be $80. To achieve this price, it is necessary to produce at least 500 thousand engines per year. European scientists are more cautious in forecasts and believe that the commercial use of hydrogen fuel cells in the automotive industry will begin no earlier than 2020.
Hydrogen H is the most common element in the Universe (about 75% by mass), on Earth it is the ninth most common element. The most important natural hydrogen compound is water.
Hydrogen ranks first in the periodic table (Z = 1). It has the simplest structure of an atom: the nucleus of an atom is 1 proton, surrounded by an electron cloud consisting of 1 electron.
Under some conditions, hydrogen exhibits metallic properties (donates an electron), in others - non-metallic (accepts an electron).
Hydrogen isotopes are found in nature: 1H - protium (the nucleus consists of one proton), 2H - deuterium (D - the nucleus consists of one proton and one neutron), 3H - tritium (T - the nucleus consists of one proton and two neutrons).
The simple substance hydrogen
The hydrogen molecule consists of two atoms linked by a non-polar covalent bond.
physical properties. Hydrogen is a colorless, non-toxic, odorless and tasteless gas. The hydrogen molecule is not polar. Therefore, the forces of intermolecular interaction in gaseous hydrogen are small. This is manifested in low boiling points (-252.6 0С) and melting points (-259.2 0С).
Hydrogen is lighter than air, D (in air) = 0.069; slightly soluble in water (2 volumes of H2 dissolve in 100 volumes of H2O). Therefore, hydrogen, when produced in the laboratory, can be collected by air or water displacement methods.
Getting hydrogen
In the laboratory:
1. Action of dilute acids on metals:
Zn +2HCl → ZnCl 2 +H 2
2. Interaction of alkali and alkaline metals with water:
Ca + 2H 2 O → Ca (OH) 2 + H 2
3. Hydrolysis of hydrides: metal hydrides are easily decomposed by water with the formation of the corresponding alkali and hydrogen:
NaH + H 2 O → NaOH + H 2
CaH 2 + 2H 2 O \u003d Ca (OH) 2 + 2H 2
4. The action of alkalis on zinc or aluminum or silicon:
2Al + 2NaOH + 6H 2 O → 2Na + 3H 2
Zn + 2KOH + 2H 2 O → K 2 + H 2
Si + 2NaOH + H 2 O → Na 2 SiO 3 + 2H 2
5. Water electrolysis. To increase the electrical conductivity of water, an electrolyte is added to it, for example, NaOH, H 2 SO 4 or Na 2 SO 4. At the cathode, 2 volumes of hydrogen are formed, at the anode - 1 volume of oxygen.
2H 2 O → 2H 2 + O 2
Industrial production of hydrogen
1. Conversion of methane with steam, Ni 800 °C (cheapest):
CH 4 + H 2 O → CO + 3 H 2
CO + H 2 O → CO 2 + H 2
In total:
CH 4 + 2 H 2 O → 4 H 2 + CO 2
2. Water vapor through hot coke at 1000 o C:
C + H 2 O → CO + H 2
CO + H 2 O → CO 2 + H 2
The resulting carbon monoxide (IV) is absorbed by water, in this way 50% of industrial hydrogen is obtained.
3. By heating methane to 350°C in the presence of an iron or nickel catalyst:
CH 4 → C + 2H 2
4. Electrolysis of aqueous solutions of KCl or NaCl as a by-product:
2H 2 O + 2NaCl → Cl 2 + H 2 + 2NaOH
Chemical properties of hydrogen
- In compounds, hydrogen is always monovalent. It has an oxidation state of +1, but in metal hydrides it is -1.
- The hydrogen molecule consists of two atoms. The emergence of a bond between them is explained by the formation of a generalized pair of electrons H: H or H 2
- Due to this generalization of electrons, the H 2 molecule is more energetically stable than its individual atoms. To break a molecule into atoms in 1 mole of hydrogen, it is necessary to expend an energy of 436 kJ: H 2 \u003d 2H, ∆H ° \u003d 436 kJ / mol
- This explains the relatively low activity of molecular hydrogen at ordinary temperature.
- With many non-metals, hydrogen forms gaseous compounds such as RN 4, RN 3, RN 2, RN.
1) Forms hydrogen halides with halogens:
H 2 + Cl 2 → 2HCl.
At the same time, it explodes with fluorine, reacts with chlorine and bromine only when illuminated or heated, and with iodine only when heated.
2) With oxygen:
2H 2 + O 2 → 2H 2 O
with heat release. At ordinary temperatures, the reaction proceeds slowly, above 550 ° C - with an explosion. A mixture of 2 volumes of H 2 and 1 volume of O 2 is called explosive gas.
3) When heated, it reacts vigorously with sulfur (much more difficult with selenium and tellurium):
H 2 + S → H 2 S (hydrogen sulfide),
4) With nitrogen with the formation of ammonia only on the catalyst and at elevated temperatures and pressures:
ZN 2 + N 2 → 2NH 3
5) With carbon at high temperatures:
2H 2 + C → CH 4 (methane)
6) Forms hydrides with alkali and alkaline earth metals (hydrogen is an oxidizing agent):
H 2 + 2Li → 2LiH
in metal hydrides, the hydrogen ion is negatively charged (oxidation state -1), that is, the hydride Na + H - is built like chloride Na + Cl -
With complex substances:
7) With metal oxides (used to restore metals):
CuO + H 2 → Cu + H 2 O
Fe 3 O 4 + 4H 2 → 3Fe + 4H 2 O
8) with carbon monoxide (II):
CO + 2H 2 → CH 3 OH
Synthesis - gas (a mixture of hydrogen and carbon monoxide) is of great practical importance, because, depending on temperature, pressure and catalyst, various organic compounds are formed, for example, HCHO, CH 3 OH and others.
9) Unsaturated hydrocarbons react with hydrogen, turning into saturated:
C n H 2n + H 2 → C n H 2n+2.
