Water structure: new experimental data. Water and its beneficial properties for living things
St. Petersburg State University of Architecture and Civil Engineering
Department of Chemistry
Properties and structure of water
Is done by a student
groups 2-B-1
Gorokhov M.V.
L. I. Akimov
St. Petersburg
1. Introduction. Water in nature ............................................ 3
2. Water structure .............................................. .............. 5
3. Properties of water .............................................. ................ eleven
4. Silver and melt water ............................................ . 20
5. Conclusion ............................................... ................... 22
6. Literature ............................................... ................... 23
Introduction Water in nature.
The most important thing for life is water.
Water is of primary importance in most chemical reactions, in particular biochemical ones. The ancient position of the alchemists - “bodies do not act until they are dissolved” - is fairly true.
The human embryo contains water,%: three-day - 97, three-month - 91, eight-month - 81. In an adult, the proportion of water in the body is 65%.
Man and animals in their bodies can synthesize primary ("juvenile") water, form it during the combustion of food products and the tissues themselves. In a camel, for example, the fat contained in the hump can produce 40 liters of water by oxidation.
The connection between water and life is so great that it even allowed V. I. Vernadsky "to consider life as a special colloidal water system ... as a special kingdom of natural waters."
The amount of water contained in living creatures is at every given moment a huge amount. For one year, tenths of a percent of the entire ocean moves by the forces of life, and in a few hundred years, masses of water exceeding the mass of the World Ocean pass through living matter.
The geochemical composition of ocean water is close to the blood composition of animals and humans (see table).
Comparative content of elements in human blood and in the oceans,%
Water is a very common substance in nature. 71% of the surface of the globe is covered with water, spitting oceans, seas, rivers and lakes. A lot of water is in a gaseous state in the form of vapor in the atmosphere; in the form of huge masses of snow and ice, it lies year-round on the tops of high mountains and in the polar countries. In the bowels of the earth is also water that permeates the soil and rocks. The total water reserves on Earth are 1,454.3 million km 3 (of which less than 2% relates to fresh water, and 0.3% is available for use).
Natural water is not completely pure. Rainwater is the most pure, but it also contains insignificant amounts of various impurities which it captures from the air.
The amount of impurities in fresh waters usually lies in the range from 0.01 to 0.1% (mass .). Sea water contains 3.5 (mass.) Dissolved substances, the main mass of which is sodium chloride (sodium chloride).
To free natural water from particles suspended in it, it is filtered through a layer of a porous substance, for example, coal, calcined clay, etc. p.
By filtration, only insoluble materials can be removed from water. Dissolved substances are removed from it by distillation (distillation) or ion exchange.
Water is very important in the life of plants, animals and humans. In every organism, water is an environment in which chemical processes take place that ensure the vital activity of the organism; besides, she herself takes part in a number of biochemical reactions.
Water is an essential component of almost all technological processes of both industrial and agricultural production.
Water structure
The English physicist Henry Cavendish discovered that hydrogen H and oxygen O form water. In 1785, French chemists Lavoisier and Meunier found that water consists of two parts by weight of hydrogen and sixteen parts by weight of oxygen.
However, one cannot think that this representation, expressed by the chemical formula H 2 O, is strictly speaking true. The hydrogen and oxygen atoms that make up natural water, or more precisely, hydrogen oxide, can have different atomic weights and vary significantly in physical and chemical properties, although they occupy the same place in the periodic system of elements.
These are the so-called isotopes. Five different hydrogens with atomic weights of 1, 2, 3, 4, 5 and three different oxygen with atomic weights of 16, 17 and 18 are known. In natural oxygen, 31 atoms of the O 16 isotope account for 5 atoms of the O 17 oxygen isotope and 1 oxygen isotope atom About 18. In natural gaseous hydrogen, 5.5 thousand atoms of light hydrogen H (protium) account for 1 atom of H 2 (deuterium). As for H 3 (tritium), as well as H 4 and H 5, they are negligible in natural water on Earth, but their participation in space processes at low temperatures in interplanetary space, in the bodies of comets, etc. is very likely.
Nuclei of isotope atoms contain the same number of protons, but different numbers of neutrons. Atomic masses of isotopes are different.
A single electron rotates around the nucleus of a hydrogen atom; therefore, the atomic number of hydrogen is unity. This electron rotates in circular orbits, which together form a sphere. There are many orbits, and depending on the location of the electron in one or another circular orbit, a hydrogen atom may have many energy states of the electron, i.e., it can be in a calm or more or less excited state.
An oxygen atom has 8 electrons (atomic number 8), 6 of which move in outer orbits, representing the shape of a figure eight or a dumbbell, and 2 in an inner circular orbit. According to the number of electrons in the nucleus of an oxygen atom, there are 8 protons, thus, the atom itself is generally neutral.
The most stable outer orbit of an atom is composed of 8 electrons, and oxygen has 6, i.e., 2 electrons are missing. At the same time, hydrogen, like oxygen, exists in molecules containing 2 atoms (H 2), interconnected by two electrons, which easily replace the vacancy of two electrons of the outer orbit of the oxygen atom, forming in aggregate a water molecule with a complete stable eight-electron outer orbit (see Figure 1.).
Figure 1. Scheme of the formation of a water molecule (b) from 1 oxygen atom and 2 hydrogen atoms (a).
Many different schemes for the formation of a water molecule can be given, based on the ideas of different physicists. In essence, there are no contradictions and fundamental differences in them. After all, in reality, no one saw the structure of atoms or the structure of a molecule, therefore hypothetical schemes are built only on the basis of indirect signs observed by devices, which suggest both the behavior and properties of atoms and molecules.
The sizes of atoms of various elements range from about 0.6 to 2.6 A, and the length of the light wave is several thousand times greater: (4.5-7.7) * 10 -5 cm. In addition, both atoms and molecules do not have clear boundaries, which explains the existing discrepancy between the calculated radii.
Under normal conditions, one would expect that the bonds of the oxygen atom with both hydrogen atoms in the H 2 O molecule form a very obtuse angle at the central oxygen atom close to 180 °. However, quite unexpectedly, this angle is not 180 °, but only 104 ° 31 ". As a result, intramolecular forces are not fully compensated and their excess appears outside the molecule. Figure 2 shows the main dimensions of the water molecule.
Figure 2. Water molecule and its size.
In the water molecule, positive and negative charges are distributed unevenly, asymmetrically. This arrangement of charges creates the polarity of the molecule. Although the water molecule is neutral, but because of its polarity it is oriented in space, taking into account the gravity of its negatively charged pole to a positive charge and its positively charged pole to a negative charge.
Inside the water molecule, this charge separation is very large compared to the charge separation of other substances. This phenomenon is called the dipole moment. These properties of water molecules (also called the dielectric constant, which is very high in H 2 O) are very important, for example, in the processes of dissolution of various substances.
The ability of water to dissolve solids is determined by its dielectric constant e, which is equal to 87.7 for water at 0 ° C; at 50 ° C - 69.9; at 100 ° C - 55.7. At room temperature, the dielectric constant is 80. This means that two opposite electric charges are mutually attracted in water, with a force equal to 1/80 of the force of their interaction in air. Thus, the separation of ions from a crystal of any salt in water is 80 times easier than in air.
But water does not consist only of molecules. The fact is that a water molecule can dissociate (split) into a positively charged hydrogen ion H + and a negatively charged hydroxyl ion OH -. Under ordinary conditions, pure water dissociates very weakly: only one molecule of 10 million water molecules decomposes into a hydrogen ion and a hydroxyl ion. However, with an increase in temperature and a change in other conditions, dissociation can be much larger.
Although water as a whole is chemically inert, the presence of H + and OH - ions makes it extremely active.
Negatively charged oxygen ions (O -) can also be in water. Moreover, other hydrogen compounds with oxygen can be found in nature. First of all, widespread negatively charged hydroxyxonium Н 3 О + belongs to such compounds. It is found in solutions of halite (NaCl) at high temperatures and pressures. Hydroxonium is located in the nodes of the ice lattice (together with the hydroxyl other OH -) in an amount (at 0 ° C) of 0.27 * 10 -9 parts, as well as in a bound state in many minerals.
H 3 O + and OH - in the deep bowels are carriers of many compounds (especially in the process of granitization). Other hydrogen compounds with oxygen include hydrogen peroxide (Н 2 О 2), perihydroxyl (НО 2), hydroxyl monohydrate (Н 3 О 2), etc. All of them are unstable under the conditions of the Earth’s surface, but at certain temperatures and pressures can be in nature for a long time, and most importantly - turn into a water molecule, as will be discussed below. Н 3 О 2 - found in the clouds of the ionosphere at an altitude of more than 100 km above sea level.
As noted above, a water molecule is usually neutral. However, when an electron is pulled out of it by beta rays (fast electrons), a charged “molecule” of water can form — a positive H 2 O + ion. When water interacts with this ion, the OH radical arises - according to the scheme:
H 2 O + + H 2 O \u003d H 3 O + + OH -.
Upon recombination of hydrooxonium Н 3 О + with an electron, an energy of 196 kcal / mol is released, sufficient for the splitting of Н 2 О into Н and ОН. Free radicals play a very important role in astrophysics and in the physics of the earth's atmosphere. On the Sun, the OH radical was discovered, and in spots in an increased amount. It is also found in the stars and in the head part of comets.
So, considering water only as a substance consisting of atoms, molecules and ions of hydrogen and oxygen, and not taking into account all other elements of the periodic system and their inorganic and organic compounds, which can be in the form of solutions, suspensions, emulsions and impurities, gaseous, liquid and solid states, 36 compounds can be distinguished - varieties of hydrogen and oxygen that make up the water. In the table. 1 shows nine isotopic varieties of water.
Some isotopic varieties of water compared with the content of individual elements in sea water
As you can see, in addition to H 2 O, there are usually not so many other isotopic varieties, only about 0.3%. Tritium (H 3, or T) is weakly radioactive, and its half-life lasts 12.3 years, it is not listed in the table, like other radioactive isotopes of hydrogen with atomic weights of 4 (H 4) and 5 (H 5) with exclusively short half-life. For example, H 4 is only 4/100000000000 sec. or 4 * 10 -11 sec.
In addition to the above four isotopes of hydrogen, there are three more radioactive isotopes of oxygen: O 14, O 15, O 16, but they also can not be of great importance in natural water, since their half-lives are very small and are estimated to take tens of seconds. But this is not all, if we talk about varieties of pure water.
So far, we have considered only atoms, molecules and ions of hydrogen and oxygen and their compounds that make up what we call pure water. In 1 cm 3 of liquid water at 0 ° C contains 3.35 * 10 22 molecules.
It turns out that water particles are far from being arbitrarily located, but form a definite structure in all three phases of water, which changes depending on temperature and pressure. We came to the most difficult to understand, mysterious and far from resolved problem of water - its structure.
Water structure models.
Several models of the structure of pure water are known, starting with the simplest associates, the ice-like model and the jelly-like masses characteristic of polypeptides and polynucleotides, an infinitely and randomly branched gel with rapidly appearing and disappearing hydrogen bonds. The choice of a specific model of liquid water depends on the properties studied. Each model conveys certain characteristic features of its structure, but cannot claim to be the only correct one.
The ice-like model of O. Ya. Samoilov corresponds to more experimental data. According to this model, the close ordering of the molecular arrangement, characteristic of water, is an ice-like tetrahedral skeleton disrupted by thermal motion, the voids of which are partially filled with water molecules. In this case, water molecules located in the voids of the ice-like framework have a different energy than the water molecules in its nodes. The tetrahedral environment of its molecules is characteristic of the water structure. Three neighbors of each molecule in liquid water are located in one layer and are located at a greater distance from it (0.294 nm) than the fourth molecule from the neighboring layer (0.276 nm). Each water molecule in the formation of an ice-like framework forms one mirror-symmetric (strong) and three centrally symmetric (less strong) bonds. The first relates to bonds between water molecules of a given layer and neighboring layers, the rest relates to bonds between water molecules of one layer. Therefore, a quarter of all bonds are mirror symmetric, and three quarters are centrally symmetric. 
The notions of the tetrahedral environment of water molecules led to the conclusion that its structure is highly openwork and that there are voids in it that are equal or larger than water molecules.
Fig 3. Elements of the structure of liquid water.
а - elementary water tetrahedron (light circles - oxygen atoms, black halves - possible positions of protons on the hydrogen bond);
b - mirror-symmetric arrangement of tetrahedrons;
c - centrally symmetric arrangement; g - the location of oxygen centers in the structure of ordinary ice.
Liquid water is characterized by significant forces of intermolecular interaction due to hydrogen bonds that form a spatial network. The hydrogen bond is due to the ability of the hydrogen atom connected to the electronegative element to form an additional bond with the electronegative atom of another molecule. The hydrogen bond is relatively strong and amounts to several kilojoules per mole. In terms of strength, it takes an intermediate place between the energy of Van der Waals and the energy of a typical ionic bond.
In a water molecule, the H-O chemical bond energy is 456 kJ / mol, and the H ... O hydrogen bond energy is 21 kJ / mol.
Fig. 4. Hydrogen bonding scheme between water molecules.
Water properties
Let us turn to a general description of the properties of water, making it the most amazing substance on Earth.
And the first, most striking, property of water is that water belongs to the only substance on our planet, which under ordinary conditions of temperature and pressure can be in three phases, or three states of aggregation: in solid (ice), liquid and gaseous ( invisible steam).
As is well known, water is taken as a model measure - the standard for all other substances. It would seem that the standard for physical constants should be to choose a substance that behaves in the most normal, ordinary way. But it turned out just the opposite.
Water is the most abnormal substance in nature.
First of all, water has an extremely high heat capacity compared to other liquids and solids. If the heat capacity of water is taken as a unit, then, for example, for alcohol and glycerin it will be only 0.3; for sand, rock salt - 0.2; for mercury and platinum - 0.03; for wood (oak, spruce, pine) - 0.6; for iron - 0.1, etc.
Thus, the water in the lake at the same air temperature and the same solar heat received by it will heat 5 times less than the dry sandy soil around the lake, but the same amount of water will retain the received heat more than the soil.
Another water anomaly is the unusually high latent heat of vaporization and latent heat of fusion, i.e. the amount of heat that is needed to turn liquid into steam and ice into liquid (in other words, the amount of heat absorbed or released). For example, to turn 1 g of ice into a liquid, it is necessary to roll about 80 cal, while the substance itself ice - water will not increase its temperature by a fraction of a degree. As you know, the temperature of the melting ice is invariably the same and equal to 0 ° C. At the same time, the water of the melting ice from the environment should absorb a relatively huge amount of heat (80 cal / g).
We observe the same jump during the transition of water to steam. Without increasing the temperature of boiling water, which will invariably (at a pressure of 1 atm.) Be equal to 100 ° C, the water itself should absorb from the environment almost 7 times more heat than when ice melts, namely: 539 cal.
If steam turns into water or water turns into ice, then the same amount of heat in calories (539 and 80) should be released from the water and warm the environment surrounding the water. In water, these values \u200b\u200bare unusually high. For example, the latent heat of vaporization of water is almost 8 times greater, and the latent heat of fusion is 27 times greater than that of alcohol.
An amazing and completely unexpected anomalous feature of water is its freezing and boiling points. If we consider a number of hydrogen compounds with other elements, for example, sulfur, selenium, tellurium, we can see that there is a pattern between their molecular weights and freezing and boiling temperatures: the higher the molecular weights, the higher the temperature values \u200b\u200b(Table 2).
The dependence of the freezing and boiling points
certain hydrogen compounds by molecular weight
An even more surprising and no less unexpected property of water is a change in its density depending on changes in temperature. All substances (except bismuth) increase their volume and decrease density with increasing temperature. In the range from + 4 ° C and above, water increases its volume and decreases its density, like other substances, but starting from + 4 ° C and lower, up to the freezing point of water, its density starts to fall again, and the volume expands, and the moment of freezing, a jump occurs, the volume of water expands 1/11 of the volume of liquid water.
The exceptional significance of such an anomaly is clear enough to everyone. If this anomaly were not there, the ice would not have been able to swim, the ponds would freeze to the bottom in winter, which would be a disaster for everyone living in the water. However, this property of water is not always pleasant for a person - freezing water in water pipes leads to their rupture.
There are many other water anomalies, for example, the temperature coefficient of expansion of water in the range from 0 to 45 ° C increases with increasing pressure, and for other bodies it is usually the opposite. Thermal conductivity, the dependence of dielectric constant on pressure, self-diffusion coefficient, and many other properties are also anomalous.
The question arises, why explain these anomalies?
The path to the explanation, perhaps, lies in revealing the features of structures formed by water molecules under various aggregate (phase) states associated with temperatures, pressures and other conditions in which water is located. Unfortunately, there is no unity in views on this issue. Most modern researchers are of the opinion of a two-structured model of water, according to which water is a mixture of:
1) loose ice-like and
2) tightly packed structures.
Ice crystals belong to hexagonal syngony, i.e. they have the form of hexagonal prisms (hexagons). In the structure of ice, each water molecule is surrounded by four molecules closest to it, located at the same distance from it. Thus, each water molecule has a coordination number.
Water molecules are arranged so that they are in contact with opposite poles (positively and negatively charged). In the structure of ice like tridymite, the distance between the molecules is 4.5 A, and in the structure of quartz type it is 4.2 A. In the first case, it is melting ice water with a temperature of about 0 ° C. In the second case, a denser packing of water molecules is assumed at a temperature + 4 ° C.
The mysterious expansion of water by about 10% during freezing is explained by the rapid change of a densely packed structure to an openwork, loose structure. Due to the low coordination number, there are many voids in the ice structure, which are even larger than the water molecules themselves. Each void is limited to 6 water molecules, and at the same time, around each water molecule in the ice structure there are 6 centers of voids.
At a temperature of about + 4 ° C, these voids are filled with "free" water molecules and its density becomes maximum. With a further increase in temperature, an increasingly loose openwork structure gradually reappears. As a result of the increasing thermal motion of the molecules (with increasing temperature), the ice structure is gradually “eroded”, weakening of hydrogen bonds occurs, and “erosion” of a tridymite-type structure intensifies, the density of water decreases, and its volume increases.
It must be emphasized once again that the internal structure of liquids in general, and water in particular, is much more complicated than that of solids and gases. The nature of water is extremely complex and still far from unraveled. Prof. O. Ya. Samoilov, a major researcher of the water structure, explains the process of a sudden increase in the volume occupied by water at the moment of freezing or a decrease in volume during ice thawing with two crude examples-analogies, of course, extremely simplified schematized.
Imagine a box in which balls with tight packing are stacked. When the box is shaken, disordering will occur, the volume occupied by the balls will increase and voids form.
The reverse process is illustrated by the following example. Let grooves and protrusions corresponding to them on other balls be made on each ball so that each ball is surrounded by only 4 balls and the protrusions do not enter the grooves. When shaking and entering the protrusions into the recesses, a sharp and instantaneous decrease in the volume occupied by all the balls will occur. This is an example of the transition of ice into water from temperatures around + 4 ° C.
In 1962, in Kostroma, associate professor N. N. Fedyakin discovered a new variety of chemically pure water (in addition to its isotopic differences). This is the so-called abnormal (“modified") water formed from ordinary in quartz capillaries or on quartz plates. Independent daughter columns of new abnormal water of high viscosity, with a reduced vapor pressure, with a viscosity and coefficient of thermal expansion, several times larger, and with a density 40% more than ordinary water, appear in the capillaries.
While abnormal water can be obtained from ordinary water by vapor condensation only on quartz. Pure abnormal water is an amorphous glassy non-crystallizing mass with the consistency of petroleum jelly.
This modified water has high stability and behaves the same as outside of capillaries. It does not freeze, remaining liquid even at - 50 ° C. At pressures of 60 thousand atm. and at a temperature of 1000 ° C it did not appear.
A new type of water does not mix with ordinary, but forms an emulsion with it. Modified water does not crystallize; it, like glass, is an amorphous mass. The mystery of its origin has not yet been solved, and scientists around the world are conducting intensive research. In any case, it is impossible to explain the origin of abnormal water with structural features. Abroad, she was called "superwater."
F. A. Letnikov and T. V. Kashcheva was discovered by the water "memory", or, "hardening." Water was carefully purified by distillation and heated to 200, 300, 400, and 500 ° C at a pressure of 1, 88, 390, and 800 atm. Temperature and pressure change the properties of water, it has been known for a long time. But what is surprising is that some new properties are preserved in water even after the removal of high temperatures and pressures. For example, in water, the ability to dissolve certain salts increased 4 times.
It has long been noticed a change in a number of properties of water when exposed to a magnetic field. The stronger the latter, the greater the changes occur with water. So, with changes in the intensity of a sufficiently strong magnetic field, the concentration of hydrogen ions (H +) doubles, and the surface tension of water - three times.
The magnetic field also affects the rate and nature of the crystallization of salts in the dissolved state in water. Magnetic treatment of water leads to a decrease in scale in boilers, reduces the wettability of surfaces of solids, changes the boiling point, viscosity, increases the rate of slurry thickening, filtration, cement hardening, and changes the magnetic susceptibility. The magnetic field significantly changes the heat of hydration in concentrated solutions (up to 5%), which is very important for deep brines.
However, the magnetic field does not affect pure water, i.e., water in the solution of which there are no electrolytes. When water is magnetized, the orientation of the nuclear spin (the angular momentum of the atomic nucleus, which is closely related to the magnetic moment) in the H 2 O molecule changes.
Magnetic water, like freshly melted, also has a "memory". Its new properties have a "half-life" of about a day. Melt water, as established by numerous observations, has an inherent increased biological activity, which persists for some time after melting. According to Kazan bionics, the new properties of both magnetic and melt water are explained by changes occurring with hydrogen nuclei.
Currently, in many countries organized the industrial production of magnetized water in large quantities.
The transition point of the liquid phase of water into solid at a pressure of 1 atm. is a temperature of 0 ° C. With increasing pressure, the point of transition of water into ice decreases at 600 atm. up to - 5 ° С, at 2200 atm. to - 22 ° C. But then the water begins to behave completely surprisingly: at 3530 atm. it passes into ice only at -17 ° C, at 6380 atm. - at + 0.16 ° C, and at 20 670 atm. ice has a temperature of + 76 ° C - hot ice that could give a burn.
The German scientist G. Tamman and the American P.V. Bridgman identified six varieties of ice:
I - ordinary ice, existing at pressures up to 2200 atm., With a further increase in pressure, goes into II;
II - ice with a decrease in volume of 18%, drowns in water, is very unstable and easily turns into III;
III - also heavier than water and can be directly obtained from ice I;
IV - lighter than water, exists at low pressures and temperatures slightly below 0 ° C, is unstable and easily passes into ice I;
V - can exist at pressures from 3600 to 6300 atm., It is denser than ice III, with increasing pressure with a bang it instantly turns into ice VI;
VI - denser than ice V, at a pressure of about 21,000 atm. has a temperature of + 76 ° C; can be obtained directly water at a temperature of + 60 ° C and a pressure of 16,500 atm.
The above pressures can exist in the geospheres to a depth of 80 km. According to V.I. Vernadsky, differences in hot ice exist in the lithosphere in the area of \u200b\u200bphysically bound waters. For example, firmly bound water has a solid density (and this at ordinary pressure) of 2 g / cm 3. Such water freezes only at - 78 ° C.
The behavior of water in nature under various conditions of pressure, temperature, electromagnetic fields, and especially differences in electric potentials and much more is mysterious, especially since natural water is not a chemically pure substance, it contains many substances in the solution (essentially all elements of the periodic system) , and besides in various concentrations. This mystery is especially great for the great depths of the Earth's lithosphere, where there are high pressures and temperatures. But even if we take “pure” water and see how its certain properties change at relatively high pressures and temperatures, then, for example, for density we get such values, g / cm 3: at 100 ° C and 100 atm., As well as at 1000 ° C and 10,000 atm. it will be the same and close to 1; at 1000 ° С and 100 atm. - 0.017; at 800 ° С and 2500 atm. - 0.5; at 770 ° C and 13,000 atm. - 1.7, and the electrical conductivity of such water is equal to the electrical conductivity of pentinormal hydrochloric acid. For brines that dominate the depths of the lithosphere, all these values \u200b\u200bwill change.
In 1969, at the astrophysical center at the University of Toledo (Ohio, USA), American scientists A. Delsemm and A. Wenger discovered a new superdense modification of ice at a temperature of –173 ° C and a pressure of about 0.007 mm Hg. Art. This ice had a density of 2.32 g / cm 3, that is, it was close in density to some varieties of gneiss (2.4 g / cm 3); it is amorphous (does not have a crystalline structure) and plays a large role in the physics of planets and comets.
The properties of water also change under the influence of an electric field of different frequencies. At the same time, the light intensity in water decreases, this is due to the absorption of its rays. Further, the evaporation rate of water changes by about 15%.
In general, recently, an increasing number of researchers based on field and laboratory observations have come to the conclusion about the significant role of the difference in natural electric potentials for the physical and chemical characteristics of natural waters. Even in the near-surface zones of the lithosphere with relatively weak electric potentials, the potential difference causes both the movement of the water itself and the cations and anions dissolved in it in mutually opposite directions. Some scientists have observed the emergence of electrical potentials (and their differences) at the contact of water and ice, as well as at sulfide deposits. At greater depths of the lithosphere, greater potential differences between different rocks and different solutions should be expected.
The American scientist P. Marx believes that powerful galvanic batteries are formed at depths of about 12 km in the presence of mineralized solutions, metals, sulfur, and graphite. The differences in electrical potentials can be so great that they decompose water into hydrogen and oxygen.
All that we have said so far about the variety of varieties of water concerned pure water, without any impurities. But chemically pure water cannot be anywhere in nature. Even after artificially distilled water, after repeated distillation, it will contain dissolved carbon dioxide, nitrogen, oxygen, as well as in a small part of the substance from which the vessel is made, where it is located.
Thus, even artificially obtaining almost pure water is very difficult, although a similar experiment at the beginning of the century was conducted by the German physicist F. Kohlrausch. He was obtained in a completely insignificant volume and for several seconds, for which it was possible to determine its electrical conductivity, absolutely pure water.
All water in nature, including snow, ice and rain, is a solution of various substances in the form of ions of neutral molecules, small and large suspensions, living things (from bacteria to large animals) and their metabolic products. If we talk about substances in water, then, for example, acad. V. I. Vernadsky, who considered water as a mineral, identified 485 types of minerals of the water group (hydrides), making a reservation that he described only a smaller part of the types of water and that their total amount would probably exceed 1500. Of course, this classification is unacceptable , for practical purposes, it is mentioned only to illustrate the diversity of the chemical composition of natural waters, considering water as a solvent and a mineral.
Natural water can be classified according to the following criteria: temperature, chemical composition of dissolved components, location, intended use, origin, circulation dynamics, phase state, location in a particular geosphere and many other properties and attributes.
1. Water is found in nature in the temperature range from almost absolute zero (that is, around –273 ° C) to about 2000 ° C. Even at ordinary pressure, water, remaining a liquid, can be supercooled to –70 ° C and not overheat, turning into steam, up to + 120 ° C, but only for a very short time.
2. All natural water is a solution of gases and minerals, and for the outer shells of the Earth (no deeper than 3-5 km) and the habitat of living organisms. Gases and solids can be dissolved in water from negligible amounts to the possible solubility limits of certain substances. Depending on temperature and pressure, everything dissolves in water, all elements of the periodic system that are found in nature, even metals and such very insoluble silicon compounds as glass, quartz, etc. can be contained in the solution.
3. All natural waters according to the chemical composition of substances in solution are most conveniently divided into three classes according to the anion predominant in the solution:
a) chloride (the most common class),
b) bicarbonate and
c) sulfate.
Each class, in turn, is divided according to the predominant cation into four groups: sodium, calcium, magnesium and potassium. Thus, we have 12 large varieties of water.
According to the gas gas prevailing in the solution, they are also divided into nitrogen, hydrogen sulfide, methane, carbon dioxide, oxygen and others.
4. Water can be in both free and bound state. Free water can pour out and move under the influence of gravity (gravity). They are called “gravitational”.
But water in the form of H 2 O or its isotopic varieties, as well as the form of OH hydroxyl, H 3 O hydroxonium, and others can be included in the minerals as physically or chemically bound, sometimes in significant quantities. So, in a physically bound state, water is present in minerals such as hydrobasaluminite Al 4 [(OH) 1 0 SO 4)] 3 · 36H 2 0 - 60 weight. %, mirabilite Na 2 SO 4 · 10H 2 0 - 56 weight. %, borax Na 2 В 4 O 7 · 10Н 2 О - 47 weight. %; in chemically bound (in the form of hydroxyl OH) - in hydrargillite Al 3 · 10H 2 O- 65 weight. %, in tremolite Ca 2 Mg 5 12 · [OH] 2 - 42 weight. %, in tourmaline (Na, Ca) Mg, Al) 6 · [B 3 Al 3 Si 6] x (O, OH) 30 - 31 wt. %
5. According to the intended purpose, the waters can be subdivided into mineral (medicinal), drinking, household, technical, thermal (for energy, medical, and heating purposes).
All of these waters can be used for the extraction of minerals (for example, iodine-bromine, potash, etc.), as communication lines (ponds, water courses), to generate electricity for irrigation (irrigation), for healing (showers, fresh baths swimming in nature) and many other purposes.
But the waters can be "harmful" - poisonous, flooding underground workings, causing avalanches, mudflows, seiches, floods.
6. By origin, primary and secondary waters are distinguished. The former arise in place, for example, even when a candle burns (СН 4 + 2O 2 \u003d 2Н 2 О + С0 2), and the latter as a result of water cycles.
7. According to the dynamics of water circulation, they can be freely flowing (for example, rivers), seeping through rocks at a higher or lower speed, etc. No water can be static (dead reserves), motionless in the geological section of time.
8. According to the phase (aggregate) state of water, they are divided into solid (snowflakes, smallest needles floating in the air, ice), liquid (soaring tiny droplets of fog and clouds, coalesced liquid masses in the seas, re, etc.) and gaseous (invisible eye vapor in the air, in underground gases), penetrating into the smallest pores and cracks of solids, and other phase states.
Silver and melt water
Silver water was used in ancient times. In any case, even 2.5 thousand years ago, the Persian king Cyrus used water stored in silver vessels during his campaigns. In India, they neutralized water by immersing hot silver in it. Indeed, the experience of millennia has shown that water, which for some time was in a silver vessel, then poured into a bottle and stored for a year, did not deteriorate.
Scientific research of silver water was first delivered in Switzerland by the Negel botanist at the end of the nineteenth century. In the twentieth century. in many countries, a lot of work has been done to study effective ways to obtain and use silver water for a wide variety of purposes. Currently, factory-made ionizers are produced in different countries to produce large quantities of silver water of various concentrations.
Silver ions have an antimicrobial effect. Silver water has been successfully used to disinfect drinking water. During the flight of astronaut V. Bykovsky, silver water was used for drinking. Silver electrolytic solution can be used to preserve milk, butter, melange, margarine, to increase the resistance of some potions, to accelerate the aging process of wines and improve their taste. Silver water serves as an effective therapeutic agent in inflammatory and purulent processes caused by bacterial infection, as well as in the treatment of gastrointestinal diseases, peptic ulcer, inflammatory processes of the nasopharynx, eyes, burns, etc. Silver water is also used by veterinary medicine for preventive and therapeutic purposes. .
No less curious is the effect on the living organism of meltwater. Its active biological effect was first discovered in the Arctic, when an intensive development of plankton was noticed when the ice melted. The water of melting ice (and of course snow) increases the productivity of crops by 1.5-2 times, the growth of young animals, has a rejuvenating effect on the body of both animals and humans.
Centers of ice structures are preserved in melt water. This is a kind of "memory" of water, which was already described above. The fact is that the ice structure of water is looser and biomolecules ideally fit into the voids of the ice lattice without damaging them, while preserving potential life functions.
It is curious that a fossil newt (hard-toothed) frozen to solid state, lying in permafrost at a depth of 14 m for about a million years, came to life.
It is assumed that the aging process is reduced to a large extent to an increasing deficit of the “ice” structure of biomolecules, which is destroyed by the influence of less structured water.
When fresh melt water is consumed, foci of an ice-like structure 20A in size freely pass through the walls of the digestive tract and can enter various organs of the person, producing a healing and rejuvenating effect on the entire body. At the same time, it was established that if the snow is melted and the melt water obtained from it boils, then it loses its stimulating effect.
Conclusion
"What is water?" - The question is far from simple. Everything that was told about her in this work is not an exhaustive answer to this question, and in many cases it is completely impossible to give a clear answer to it yet. For example, the question of the structure of water, the causes of numerous water anomalies, and, probably, many more properties and varieties of water that we don’t even suspect remain open. Unambiguously, we can only say that water is the most unique substance on earth.
Recall the words of our brilliant compatriot Acad. V. I. Vernadsky about the fact that "we must wait for the special exceptional nature of the physicochemical properties of water among all other compounds, which is reflected in its position in the universe and the structure of the universe."
Literature :
1. Derpolts VF Water in the universe. - L .: "Nedra", 1971.
2. Krestov G. A. From crystal to solution. - L .: Chemistry, 1977.
3. Khomchenko G.P. Chemistry for applicants to universities. - M., 1995.
Water can be in three states of aggregation - gaseous, liquid and solid. In each of these states, the water structure is not the same. Depending on the composition of the substances in it, water acquires new properties. The solid state of water can also be of at least two types: crystalline — ice and non-crystalline — glassy, \u200b\u200bamorphous (vitrification state). When instantly frozen with, for example, liquid nitrogen, the molecules do not have time to build into a crystal lattice, and the water becomes a solid glassy state. It is this property of water that allows living organisms to be frozen without damage, such as unicellular algae, Mpіut moss leaves, consisting of two layers of cells. Freezing with the formation of crystalline water leads to cell damage.
The crystalline state of water is characterized by a wide variety of forms. It has long been observed that the crystalline structures of water resemble radiolarians, fern leaves, and cysts. On this occasion, A. A. Lyubishchev suggested that the laws of crystallization are somewhat similar to the laws of the formation of living structures.
Physical properties of water. Water is the most abnormal substance, although it is taken as a standard measure of density and volume for other substances.
Density. All substances increase volume when heated, while reducing density. However, at a pressure of 0.1013 MPa (1 atm.), The water in the range from 0 to 4 0 C decreases with increasing temperature and the maximum density is observed (at this temperature 1 cm 3 of water we have a mass of 1 g). When freezing, the volume of water increases sharply by 11%, and when ice melts at 0 ° C, it also decreases sharply. With increasing pressure, the freezing temperature of water decreases every 13.17 MPa (130 atm.) By 10 ° C. Therefore, at great depths at subzero temperatures, water in the ocean does not freeze. With increasing temperature to 100 0 С, the density of liquid water decreases by 4% (at 4 ° С its density is 1).
Boiling and freezing (melting) points. At a pressure of 0.1013 MPa (1 atm.), The freezing and boiling points of water are at 0 ° C and 100 ° C, which sharply distinguishes H20 from hydrogen compounds with elements of group VI of the Mendeleev’s periodic system. In a series of Н2Те, H2Se, H2S, etc. with an increase in the relative molecular weight, the boiling and freezing points of these substances increase. Subject to this rule, water should have freezing points between - 90 and - 120 ° С, and boiling points - between 75 and 100 ° С. The boiling point of water increases with increasing pressure, and the freezing (melting) temperature drops (Appendix 1).
Heat of fusion. The latent heat of melting ice is very high - about 335 J / g (for iron - 25, for sulfur - 40). This property is expressed, for example, in the fact that ice at normal pressure can have a temperature of from - 1 to - 7 ° C. The latent heat of vaporization of water (2.3 kJ / g) is almost 7 times higher than the latent heat of fusion.
Heat capacity. The heat capacity of water (i.e., the amount of heat required to increase the temperature by 1 ° C) is 5-30 times higher than that of other substances. Only hydrogen and ammonia have a higher heat capacity. In addition, only in liquid water and mercury does the specific heat decrease with increasing temperature from 0 to 35 ° C (then begins to increase). The specific heat capacity of water at 16 ° C is conventionally taken as a unit, serving as a standard for other substances. Since the heat capacity of sand is 5 times less than that of liquid water, when the sun is equally heated, the water in the pond heats up 5 times weaker than the sand on the shore, but retains heat the same amount of time. The high heat capacity of water protects plants from a sharp increase in temperature at high air temperatures, and the high heat of vaporization is involved in thermoregulation in plants.
High melting and boiling points, high heat capacity indicate a strong attraction between neighboring molecules, as a result of which liquid water has a large internal cohesion.
Water as a solvent. The polarity of a water molecule determines its ability to dissolve substances better than other liquids. The dissolution of crystals of inorganic salts is carried out due to the hydration of their constituent ions. Organic substances are well soluble in water, with carboxylic and hydroxyl. Carbonyl and with other groups, which water forms hydrogen bonds. (adj. 1)
Water in the plant is both in a free and bound state (Appendix 2). Free water is mobile, it has almost all the physicochemical properties of pure water, and penetrates well through cell membranes. There are special membrane proteins that form channels permeable to water (aquaporins) inside the membrane. Free water enters into various biochemical reactions, evaporates during transpiration, and freezes at low temperatures.
Bound water - has altered physical properties mainly as a result of interaction with non-aqueous components. Conditionally take under bound water one that does not freeze when the temperature drops to -10 ° C.
Bound water in plants happens:
1) Osmotically linked
2) Colloidal bound
3) Capillary bound
Osmotically-bound water - bound to ions or low molecular weight substances. Water hydrates dissolved substances - ions, molecules. Water electrostatically binds and forms a monomolecular layer of primary hydration. Vacuolar juice contains sugars, organic acids and their salts, inorganic cations and anions. These substances retain water osmotically.
Colloidal-bound water - includes water that is inside the colloidal system and water that is on the surface of the colloids and between them, as well as immobilized water. Immobilization is a mechanical capture of water during conformational changes of macromolecules or their complexes, while water is enclosed in a confined space of the macromolecule. A significant amount of colloidal bound water is located on the surface of the fibrils of the cell wall, as well as in the cytoplasmic biocolloids and the matrix of cell membrane structures.
Water that hydrates colloidal particles (primarily proteins) is called colloidal bound, and dissolved substances (mineral salts, sugars, organic acids, etc.) are called osmotically bound. Some researchers believe that all the water in the cell is more or less connected. Physiologists conventionally understand by bound water that which does not freeze when the temperature drops to -10 ° C. It is important to note that any binding of water molecules (the addition of dissolved substances, hydrophobic interactions, etc.) reduces their energy. This is what underlies the reduction in cell water potential compared to pure water.
The water content in various organs of plants varies widely. It varies depending on environmental conditions, age and type of plants. So, the water content in lettuce is 93-95%, corn - 75-77%. The amount of water varies in different organs of plants: in the leaves of sunflower water contains 80-83%, in the stems - 87-89%, in the roots - 73-75%. A water content of 6–11% is characteristic mainly of air-dried seeds, in which vital processes are inhibited. Water is contained in living cells, in the dead elements of xylem and in intercellular spaces. In the intercellular spaces, water is in a vaporous state. The main evaporative organs of the plant are leaves. In this regard, it is natural that the greatest amount of water fills the intercellular spaces of the leaves. In the liquid state, water is in various parts of the cell: the cell membrane, vacuoles, and protoplasm. Vacuoles are the most water-rich part of the cell, where its content reaches 98%. With the greatest water content, the water content in the protoplasm is 95%. The lowest water content is characteristic of cell membranes. Quantifying the water content in cell membranes is difficult; apparently, it ranges from 30 to 50%.
The forms of water in different parts of the plant cell are also different. In vacuolar cell juice, water is predominant, retained by relatively low molecular weight compounds (osmotically bound) and free water. In the membrane of a plant cell, water is bound mainly by high-polymer compounds (cellulose, hemicellulose, pectin substances), i.e., colloid-bound water. In the cytoplasm itself there is free water, colloid- and osmotic-associated. Water located at a distance of 1 nm from the surface of the protein molecule is firmly bound and does not have the correct hexagonal structure (colloidal bound water). In addition, in the protoplasm there is a certain amount of ions, and, therefore, part of the water is osmotically connected.
The physiological significance of free and bound water is different. Most researchers believe that the intensity of physiological processes, including growth rates, depends primarily on the content of free water. There is a direct correlation between the content of bound water and the resistance of plants to adverse environmental conditions. These physiological correlations are not always observed.
Water in our lives is the most common and most common substance. The human body consists of water at 70%, and the natural environment around us also contains 70% of water.
From school books, we know that a water molecule consists of an oxygen atom and two hydrogen atoms, i.e. one of the smallest and lightest molecules. For all the routine and obviousness for us of the properties of water that we constantly use, there are paradoxes of liquid water that determine even life forms on Earth.
Liquid water has a density greater than the density of ice. Therefore, when freezing, the volume of ice increases, ice floats on the surface of the water.
The density of water is maximum at 4 ° C, and not at the melting point, decreases both to the right and to the left of this temperature.
The viscosity of water decreases with increasing pressure.
The boiling point of water is outside the general dependence of the boiling point on the molecular weight of substances (Fig. 1.1). Otherwise, it should not be higher than 60 ° C.
The heat capacity of water is at least twice as high as that of any other liquid.
The heat of vaporization (~ 2250 kJ / kg) is at least three times higher than that of any other liquid, 8 times more than that of ethanol.
Consider this last property of water. The heat of vaporization is the energy needed to break the bonds between molecules during their transition from the condensed phase to the gaseous one. This means that the reason for all the paradoxical properties is the nature of the intermolecular bonds of water, and this, in turn, is determined by the structure of the water molecule.
Fig.1.1. The range of molecular weight ratios of various compounds and their boiling points.
What is it - a water molecule?
In 1780 Lavoisier experimentally established that water consists of oxygen and hydrogen, that two volumes of hydrogen interact with one volume of oxygen, and that the ratio of the masses of hydrogen and oxygen in water is 2:16. By 1840, it became clear that the molecular formula of water was H 2 O.
Three nuclei in a molecule form an isosceles triangle with two protons at the base (Fig. 1.2). The electronic formula of the water molecule is [(1S 2)] [(1S 2) (2S 2) (2P 4)].
Figure 1.2.Formation of a binding system from 2p orbitals of the oxygen atom and 1s-orbitals of the oxygen atom and 1s-orbitals of hydrogen atoms.
Due to the participation of two electrons of hydrogen 1s in connection with two electrons 2p of oxygen, sp hybridization occurs and hybrid sp 3 orbitals are formed with a characteristic angle between them of 104.5 °, as well as two poles of opposite charges. The O – H bond length is 0.95 Å (0.095 nm), and the distance between protons is 1.54 Å (0.154 nm). Figure 1.3 shows an electronic model of a water molecule.
Fig. 1.3. Electronic model of the molecule H 2 ABOUT.
Eight electrons rotate in pairs in four orbitals located in three planes (angles 90 about ) that fit into the cube. 1, 2 - lone pairs of electrons.
The most important consequence of this consideration: the asymmetric distribution of charges turns the H 2 O molecule into a dipole: protons are placed at two positive ends, and lone pairs of p-electrons of oxygen are placed at two negative ends.
Thus, a water molecule can be considered as a triangular pyramid - a tetrahedron, at the corners of which four charges are placed - two positive and two negative.
These charges form their closest environment, deploying neighboring water molecules in a strictly defined way - so that between two oxygen atoms there is always only one hydrogen atom. It is easiest to imagine and study such an intermolecular structure on water in the solid state. Figure 1.4 shows the ice structure.
Fig. 1.4. Hexagonal ice structure
The structure is fastened with the help of bonds OH ... Oh. Such a combination of two oxygen atoms of neighboring water molecules through a single hydrogen atom is called a hydrogen bond.
Hydrogen bonding occurs for the following reasons:
1 - the proton has only one electron, therefore the electron repulsion of two atoms is minimal. The proton is simply immersed in the electron shell of a neighboring atom, reducing the distance between atoms by 20-30% (up to 1 Å);
2 - the neighboring atom must have a large value of electronegativity. In conditional values \u200b\u200b(according to Pauling), the electronegativity is F– 4.0; O - 3.5; N– 3.0; Cl– 3.0; C– 2.5; S– 2.5.
A water molecule can have four hydrogen bonds, in two it acts as an electron donor, in two - as an electron acceptor. And these bonds can arise both with neighboring water molecules, and with other substances.
So, the dipole moment, the angle Н-О-Н and the hydrogen bond О-Н ... О determine the unique properties of water and play a major role in the formation of the world around us.
Ph.D. O.V. Mosin
The water molecule is a small dipole containing positive and negative charges at the poles. Since the mass and charge of the oxygen nucleus are greater than those of hydrogen nuclei, the electron cloud is contracted toward the oxygen nucleus. In this case, the hydrogen nuclei are “exposed”. Thus, the electron cloud has an inhomogeneous density. Near hydrogen nuclei there is a lack of electron density, and on the opposite side of the molecule, near the oxygen nucleus, an excess of electron density is observed. It is this structure that determines the polarity of the water molecule. If you connect the epicenters of positive and negative charges with straight lines, you get a three-dimensional geometric figure - a regular tetrahedron.
The structure of the water molecule (figure to the right)
Due to the presence of hydrogen bonds, each water molecule forms a hydrogen bond with 4 neighboring molecules, forming an openwork mesh frame in the ice molecule. However, in the liquid state, water is a disordered liquid; these hydrogen bonds are spontaneous, short-lived, break quickly and form again. All this leads to heterogeneity in the structure of water.
Hydrogen bonds between water molecules (picture below left)
The fact that water is heterogeneous in composition has been established long ago. It has long been known that ice floats on the surface of water, that is, the density of crystalline ice is less than the density of a liquid.
In almost all other substances, the crystal is denser than the liquid phase. In addition, after melting with increasing temperature, the density of water continues to increase and reaches a maximum at 4 ° C. The anomaly of water compressibility is less known: when heated from the melting point up to 40 ° C, it decreases and then increases. The heat capacity of water also monotonously depends on temperature.
In addition, at temperatures below 30 ° C, with an increase in pressure from atmospheric to 0.2 GPa, the viscosity of water decreases, and the self-diffusion coefficient, a parameter that determines the speed of movement of water molecules relative to each other, increases.
For other liquids, the dependence is the opposite, and almost never happens that some important parameter does not behave monotonously, i.e. first grew, and after passing a critical temperature or pressure value decreased. There was an assumption that in fact water is not a single liquid, but a mixture of two components that differ in properties, for example, density and viscosity, and therefore, structure. Such ideas began to arise at the end of the XIX century, when a lot of data on water anomalies accumulated.
The first idea that water consists of two components was expressed by Whiting in 1884. His authorship is quoted by E.F. Fritzman in the monograph “The Nature of Water. Heavy Water ”published in 1935. In 1891, W. Rengten introduced the idea of \u200b\u200btwo states of water, which differ in density. After it a lot of works appeared, in which water was considered as a mixture of associates of different composition (“hydroles”).
When the ice structure was determined in the 1920s, it turned out that water molecules in a crystalline state form a three-dimensional continuous network in which each molecule has four nearest neighbors located at the vertices of a regular tetrahedron. In 1933, J. Bernal and P. Fowler suggested that a similar grid exists in liquid water. Since water is denser than ice, they believed that the molecules in it are located not like in ice, that is, like silicon atoms in the tridymite mineral, but like silicon atoms in a denser modification of silica - quartz. The increase in water density upon heating from 0 to 4 ° C was explained by the presence of a tridymite component at a low temperature. Thus, the Bernal-Fowler model retained the element of two-structured structure, but their main achievement is the idea of \u200b\u200ba continuous tetrahedral mesh. Then the famous aphorism of I. Langmuir appeared: “The ocean is one large molecule”. Excessive specification of the model did not add supporters of the theory of a single grid.
Only in 1951 did J. Pople create a continuous mesh model that was not as specific as the Bernal-Fowler model. Pople presented water as a random tetrahedral network, the bonds between the molecules in which are curved and have different lengths. Pople's model explains the compaction of water during melting by the curvature of bonds. When the first definitions of the structure of ices II and IX appeared in the 60–70s, it became clear how the curvature of bonds could lead to a densification of the structure. The Pople model could not explain the nonmonotonic dependence of the properties of water on temperature and pressure as well as the models of two states. Therefore, the idea of \u200b\u200btwo states has long been shared by many scientists.
But in the second half of the 20th century, it was impossible to fantasize about the composition and structure of “hydro-roles”, as they did at the beginning of the century. It was already known how ice and crystalline hydrates are arranged, and much was known about the hydrogen bond. In addition to the “continuum” models (Popla model), two groups of “mixed” models arose: cluster and clathrate models. In the first group, water appeared in the form of clusters of molecules bound by hydrogen bonds that floated in a sea of \u200b\u200bmolecules that did not participate in such bonds. Models of the second group considered water as a continuous network (usually in this context called the framework) of hydrogen bonds, which contains voids; they contain molecules that do not form bonds with carcass molecules. It was not difficult to choose such properties and concentrations of two microphases of cluster models or the properties of the framework and the degree of filling of its voids in the clathrate models to explain all the properties of water, including the famous anomalies.
Among the cluster models, the most striking was the model of G. Nemety and H. Sheragi: The pictures they proposed depicting clusters of bound molecules that float in a sea of \u200b\u200bunbound molecules are included in many monographs.
The first model of the clathrate type in 1946 was proposed by O.Ya. Samoilov: in water, a network of hydrogen bonds similar to hexagonal ice is preserved, the cavities of which are partially filled with monomeric molecules. L. Pauling in 1959 created another option, suggesting that the basis of the structure can serve as a network of bonds inherent in some crystalline hydrates.
During the second half of the 60s and the beginning of the 70s, a rapprochement of all these views was observed. Variants of cluster models appeared in which in both microphases the molecules are connected by hydrogen bonds. Proponents of clathrate models began to allow the formation of hydrogen bonds between void and frame molecules. That is, in fact, the authors of these models consider water as a continuous network of hydrogen bonds. And we are talking about how heterogeneous this grid is (for example, in density). The concept of water as hydrogen-bonded clusters floating in a sea without bonds of water molecules was put to an end in the early eighties when G. Stanley applied the percolation theory to the water model, which describes the phase transitions of water.
In 1999, the famous Russian water researcher S.V. Zenin defended his doctoral dissertation at the Institute of Biomedical Problems of the Russian Academy of Sciences, dedicated to cluster theory, which was an essential step in promoting this area of \u200b\u200bresearch, the complexity of which is enhanced by the fact that they are at the junction of three sciences: physics, chemistry and biology. He based on data obtained by three physicochemical methods: refractometry (S.V. Zenin, B.V. Tyaglov, 1994), high performance liquid chromatography (S.V. Zenin et al., 1998) and proton magnetic resonance (C .V. Zenin, 1993) a geometric model of the main stable structural formation of water molecules (structured water) was built and proved, and then (S.V. Zenin, 2004) an image was obtained using a phase contrast microscope of these structures.
Now science has proved that the features of the physical properties of water and the numerous short-lived hydrogen bonds between neighboring hydrogen and oxygen atoms in a water molecule create favorable opportunities for the formation of special associate structures (clusters) that perceive, store and transmit a wide variety of information.
The structural unit of such water is a cluster consisting of clathrates, the nature of which is due to the distant Coulomb forces. The cluster structure encoded information on the interactions that took place with these water molecules. In water clusters, due to the interaction between covalent and hydrogen bonds between oxygen atoms and hydrogen atoms, proton (H +) migration can occur via the relay mechanism, leading to proton delocalization within the cluster.
Water, consisting of many clusters of various types, forms a hierarchical spatial liquid crystal structure, which can perceive and store vast amounts of information.
The figure (V.L. Voeikov) shows, as an example, the schemes of several simple cluster structures.
Some possible structures of water clusters
Information carriers can be physical fields of various nature. Thus, the possibility of remote information interaction of the liquid crystal structure of water with objects of various nature using electromagnetic, acoustic and other fields has been established. The acting object can be a person.
Water is a source of super-weak and weak alternating electromagnetic radiation. The least chaotic electromagnetic radiation is generated by structured water. In this case, the induction of the corresponding electromagnetic field can occur, which changes the structural and informational characteristics of biological objects.
In recent years, important data have been obtained on the properties of supercooled water. It is very interesting to study water at a low temperature, since it can be more subcooled than other liquids. Crystallization of water, as a rule, begins on some kind of heterogeneity - either on the walls of the vessel, or on floating particles of solid impurities. Therefore, it is not easy to find the temperature at which supercooled water spontaneously crystallizes. But scientists managed to do this, and now the temperature of the so-called homogeneous nucleation, when the formation of ice crystals occurs simultaneously throughout the volume, is known for pressures up to 0.3 GPa, that is, capturing the areas of existence of ice II.
From atmospheric pressure to the boundary separating ice I and II, this temperature drops from 231 to 180 K, and then slightly increases - up to 190K. Below this critical temperature, liquid water is not possible in principle.
Ice structure (picture on the right)
However, one riddle is associated with this temperature. In the mid-eighties, a new modification of amorphous ice was discovered - high-density ice, and this helped revive the concept of water as a mixture of two states. As prototypes, not crystalline structures were considered, but structures of amorphous ices of different densities. In the most intelligible form, this concept was formulated by E.G. Ponyatovsky and V.V. Sinitsin, who wrote in 1999: “Water is considered as a regular solution of two components, the local configurations of which correspond to the short-range order of amorphous ice modifications.” Moreover, by studying the short-range order in supercooled water at high pressure by neutron diffraction methods, scientists were able to find components corresponding to these structures.
The polymorphism of amorphous ices has also led to assumptions about the separation of water into two immiscible components at a temperature below a hypothetical low-temperature critical point. Unfortunately, according to researchers, this temperature at a pressure of 0.017 GPa is 230K — lower than the nucleation temperature, so no one has yet been able to observe the separation of liquid water. Thus, the revival of the model of two states raised the question of the heterogeneity of the network of hydrogen bonds in liquid water. To understand this heterogeneity is possible only with the help of computer simulation.
Speaking about the crystalline structure of water, it should be noted that 14 modifications of ice are known, most of which are not found in nature, in which water molecules retain their individuality and are connected by hydrogen bonds. On the other hand, there are many variations of the network of hydrogen bonds in clathrate hydrates. The energies of these nets (high-pressure ice and clathrate hydrates) are not much higher than the energies of cubic and hexagonal ices. Therefore, fragments of such structures can also appear in liquid water. Countless different non-periodic fragments can be constructed, the molecules of which have four nearest neighbors located approximately at the vertices of the tetrahedron, but their structure does not correspond to the structures of known ice modifications. As shown by numerous calculations, the interaction energies of molecules in such fragments will be close to each other, and there is no reason to say that some structure should prevail in liquid water.
Structural studies of water can be studied by various methods; spectroscopy of proton magnetic resonance, infrared spectroscopy, x-ray diffraction, etc. For example, the diffraction of x-rays and neutrons in water has been studied many times. However, these experiments cannot give detailed information about the structure. Inhomogeneities that differ in density could be seen by the scattering of x-rays and neutrons at small angles, but such inhomogeneities should be large, consisting of hundreds of water molecules. One could see them, and exploring the scattering of light. However, water is an exceptionally clear liquid. The only result of diffraction experiments is the radial distribution function, that is, the distance between the atoms of oxygen, hydrogen and oxygen-hydrogen. It can be seen from them that there is no long-range order in the arrangement of water molecules. These functions fade out much faster for water than for most other liquids. For example, the distribution of distances between oxygen atoms at a temperature close to room temperature gives only three maxima, 2.8, 4.5, and 6.7 Å. The first maximum corresponds to the distance to the nearest neighbors, and its value is approximately equal to the length of the hydrogen bond. The second maximum is close to the average length of the edge of the tetrahedron - recall that water molecules in hexagonal ice are located on the tops of the tetrahedron described around the central molecule. And the third maximum, expressed very weakly, corresponds to the distance to the third and more distant neighbors in the hydrogen network. This maximum itself is not very bright, but there is no need to talk about further peaks. There have been attempts to obtain more detailed information from these distributions. So in 1969 I.S. Andrianov and I.Z. Fisher found distances up to the eighth neighbor, while up to the fifth neighbor it was 3 Å, and up to the sixth - 3.1 Å. This allows you to make data on the distant surroundings of water molecules.
Another method for studying the structure — neutron diffraction by water crystals — is carried out in exactly the same way as x-ray diffraction. However, due to the fact that the neutron scattering lengths differ for different atoms not so much, the method of isomorphic substitution becomes unacceptable. In practice, they usually work with a crystal in which the molecular structure is already approximately established by other methods. Then, neutron diffraction intensities are measured for this crystal. Based on these results, the Fourier transform is carried out, during which the measured neutron intensities and phases are calculated, taking into account non-hydrogen atoms, i.e. oxygen atoms whose position in the structure model is known. Then, on the Fourier map thus obtained, the hydrogen and deuterium atoms are represented with much larger weights than on the electron density map, because the contribution of these atoms to neutron scattering is very large. Using this density map, you can, for example, determine the positions of hydrogen atoms (negative density) and deuterium (positive density).
A variation of this method is possible, which consists in the fact that a crystal formed in water is kept in heavy water before measurements. In this case, neutron diffraction not only allows you to establish where the hydrogen atoms are located, but also reveals those that can be exchanged for deuterium, which is especially important when studying isotopic (H-D) exchange. Such information helps confirm the correctness of the structure.
Other methods also allow studying the dynamics of water molecules. These are experiments on quasielastic neutron scattering, ultrafast IR spectroscopy and the study of water diffusion using NMR or labeled deuterium atoms. The NMR spectroscopy method is based on the fact that the nucleus of a hydrogen atom has a magnetic moment - a spin interacting with magnetic fields, constant and variable. From the NMR spectrum, one can judge in what environment these atoms and nuclei are located, thus obtaining information about the structure of the molecule.
As a result of experiments on quasielastic neutron scattering in water crystals, the most important parameter was measured - the self-diffusion coefficient at various pressures and temperatures. To judge the coefficient of self-diffusion by quasielastic neutron scattering, it is necessary to make an assumption about the nature of the motion of molecules. If they move in accordance with the model of Ya.I. Frenkel (a famous Russian theoretical physicist, author of the “Kinetic theory of liquids” - a classical book translated into many languages), also called the “jump-wait” model, then the time of the “settled” life (time between jumps) of the molecule is 3.2 picoseconds . The latest methods of femtosecond laser spectroscopy made it possible to estimate the lifetime of a broken hydrogen bond: a proton requires 200 fs in order to find a partner. However, all these are average values. It is possible to study the details of the structure and nature of the movement of water molecules only with the help of computer simulation, sometimes called a numerical experiment.
This is how the water structure looks according to the results of computer modeling (according to the data of Dr. G. G. Malenkova). The general disordered structure can be divided into two types of regions (shown by dark and light balls), which differ in their structure, for example, by the volume of the Voronoi polyhedron (a), the degree of tetrahedrality of the nearest environment (b), the value of potential energy (c), and also by the presence of four hydrogen bonds in each molecule (g). However, these areas literally in a moment, after a few picoseconds, will change their location.
Modeling is carried out as follows. The structure of ice is taken and heated until it melts. Then, after some time, so that the water "forgot" about its crystalline origin, instant micrographs are taken.
To analyze the structure of water, three parameters are selected:
- the degree of deviation of the local environment of the molecule from the vertices of the regular tetrahedron;
-potential energy of molecules;
-volume of the so-called Voronoi polyhedron.
To build this polyhedron, take an edge from a given molecule to the nearest one, divide it in half and draw a plane perpendicular to the edge through this point. It turns out the volume per one molecule. The volume of a polyhedron is density, tetrahedrality is the degree of distortion of hydrogen bonds, and energy is the degree of stability of the configuration of molecules. Molecules with close values \u200b\u200bof each of these parameters tend to group together into separate clusters. Regions with both low and high density have different energy values, but can have the same values. Experiments have shown that regions with different structures of clusters arise spontaneously and spontaneously decay. The whole structure of water lives and constantly changes, and the time during which these changes occur is very small. The researchers monitored the movements of the molecules and found that they make irregular vibrations with a frequency of about 0.5 ps and an amplitude of 1 angstrom. Rare slow jumps to angstroms, which last picoseconds, were also observed. In general, in 30 ps the molecule can shift by 8-10 angstroms. The lifetime of the local environment is also short. Regions composed of molecules with close values \u200b\u200bof the volume of the Voronoi polyhedron can decay in 0.5 ps, and several picoseconds can live. But the distribution of the lifetimes of hydrogen bonds is very large. But this time does not exceed 40 ps, \u200b\u200band the average value is a few ps.
In conclusion, it should be emphasized that the theory of the cluster structure of water has many pitfalls. For example, Zenin suggests that the main structural element of water is a cluster of 57 molecules formed by the fusion of four dodecahedrons. They have common faces, and their centers form a regular tetrahedron. The fact that water molecules can be located at the tops of the pentagonal dodecahedron has long been known; such a dodecahedron is the basis of gas hydrates. Therefore, there is nothing surprising in the assumption of the existence of such structures in water, although it has already been said that no concrete structure can be predominant and exist for a long time. Therefore, it is strange that this element is assumed to be the main one and that exactly 57 molecules enter it. From balls, for example, it is possible to assemble the same structures that consist of dodecahedrons adjacent to each other and contain 200 molecules. Zenin claims that the process of three-dimensional polymerization of water stops at 57 molecules. Larger associates, in his opinion, should not be. However, if this were so, crystals of hexagonal ice, which contain a huge number of molecules bound together by hydrogen bonds, could not precipitate from water vapor. It is completely unclear why the growth of the Zenin cluster stopped at 57 molecules. In order to get away from contradictions, Zenin packs the clusters into more complex formations - rhombohedrons - from almost a thousand molecules, and the initial clusters do not form hydrogen bonds with each other. Why? How do molecules on their surface differ from those inside? According to Zenin, the pattern of hydroxyl groups on the surface of rhombohedrons provides the memory of water. Consequently, the water molecules in these large complexes are rigidly fixed, and the complexes themselves are solids. Such water will not flow, and its melting point, which is associated with the molecular mass, must be very high.
What water properties does the Zenin model explain? Since the model is based on tetrahedral structures, it can be harmonized to one degree or another with data on the diffraction of X-rays and neutrons. However, it is unlikely that the model can explain the decrease in density during melting - the packing of dodecahedrons is less dense than ice. But the most difficult model is consistent with dynamic properties - fluidity, a large value of the self-diffusion coefficient, short correlation and dielectric relaxation times, which are measured in picoseconds.
Ph.D. O.V. Mosin
References:
G.G. Malenkov. Advances in Physical Chemistry, 2001
S.V. Zenin, B.M. Polanuer, B.V. Tyaglov. Experimental evidence for water fractions. G. Homeopathic medicine and acupuncture. 1997.No2.P. 42-46.
S.V. Zenin, B.V. Tyaglov. Hydrophobic model of the structure of associates of water molecules. J. Physical Chemistry. 1994.T.68.№4.P. 636-641.
S.V. Zenin The study of the structure of water by proton magnetic resonance. Dokl.RAN. 19933.T.332.№3.P.328-329.
S.V. Zenin, B.V. Tyaglov. The nature of the hydrophobic interaction. The appearance of orientational fields in aqueous solutions. Zh.Fiz.chemii. 1994.T.68.№3.P.500-503.
S.V. Zenin, B.V. Tyaglov, G. B. Sergeev, Z.A. Shabarova. The study of intramolecular interactions in nucleotide amides by NMR. Materials of the 2nd All-Union Conf. By dynamic. Stereochemistry. Odessa. 1975. P. 53.
S.V. Zenin. The structured state of water as a basis for managing the behavior and safety of living systems. Thesis. Doctor of Biological Sciences. State Scientific Center "Institute of Biomedical Problems" (SSC "IBMP"). Protected 1999. 05. 27. UDC 577.32: 57.089.001.66.207 s.
IN AND. Slesarev. Report on the implementation of research
Candidate of Chemical Sciences Alexander Smirnov, Professor of MIREA.
Mysterious power given to water
To be the juice of life on earth.
Leonardo da Vinci
Fig. 1. The structure of water at a temperature of 20 aboutC, horizontal size - 400 microns. White spots are emulsions.
Fig. 2. The structure of aqueous solutions at 20 aboutC: A — distilled water; B - degassed mineral water of Borjomi; B - alcohol tincture of 70%.
Fig. 3. Emulsions in bidistilled water at temperatures of 4 aboutC (A), 20 aboutS (B), 80 aboutC (B). Image sizes 1.5 × 1.5 mm.
Fig. 4. Change in the amplitude of acoustic emission signals and water temperature during ice melting.
Fig. 5. The relative change in temperature when heating water.
Details for the curious. Scheme of experience. In a short time, 0.5 grams of water flowed out of a cup with a positive electrode (anode) through the "bridge".
The “floating water bridge” is about 3 centimeters long.
An electrified glass rod distorts the shape of the “bridge” and breaks it into trickles.
This may look like emulsions, forming a filiform structure of the "bridge".
It is customary to consider water both as a practically neutral solvent in which biochemical reactions take place, and as a substance that carries various substances throughout the body of living organisms. At the same time, water is an indispensable participant in all physicochemical processes and, due to its great importance, is the most studied substance. The study of the properties of water has repeatedly led to unexpected results. It would seem, what surprises can the simple reaction of hydrogen oxidation 2H 2 + O 2 → 2H 2 O be fraught with? But the work of Academician N. N. Semenov showed that this reaction is branched, chain. This was more than seventy years ago, and they still did not know about the chain reaction of uranium fission. The water in a glass, river or lake is not just huge quantities of individual molecules, but their associations, supramolecular structures - clusters. To describe the structure of water, a number of models have been proposed that more or less correctly explain only some of its properties, and, in relation to others, contradict the experiment.
in theory, clusters are usually calculated only for a few hundred molecules or for layers near the interface. However, a number of experimental facts indicate that giant structures of molecular scale can exist in water (works by Corresponding Member of the Russian Academy of Sciences E. E. Fesenko).
In carefully purified doubly distilled water and some solutions, we were able to detect by acoustic emission and using laser interferometry visualize structural formations consisting of five fractions from 1 to 100 microns in size. The experiments made it possible to establish that each solution has its own structure unique to it (Fig. 1, 2).
Supramolecular complexes are formed by hundreds of thousands of water molecules grouped around hydrogen and hydroxyl ions in the form of ion pairs. For these supramolecular complexes, we offer the name "emulsions" to emphasize their similarity with the particles forming the emulsion. The complexes consist of separate fractions from 1 to 100 microns in size, and fractions having sizes of 30, 70 and 100 microns are much larger than the others.
The content of individual fractions of emulsions depends on the concentration of hydrogen ions, temperature, concentration of the solution and the history of the sample (Fig. 3). In double-distilled water at 4 ° C, the complexes are densely packed and form a texture resembling parquet. As you know, water at this temperature has a maximum density. With an increase in temperature to 20 ° C, significant changes occur in the structure of water: the number of free emulsions becomes the largest. With further heating, they gradually collapse, their number decreases, and this process basically ends at 75 ° C, when the speed of sound in water reaches a maximum.
Due to the long range of electrostatic forces, emulsions in water form a rather stable superlattice, which, however, is sensitive to electromagnetic, acoustic, thermal and other external influences.
The detected supramolecular complexes consistently include all previously obtained data on the organization of water in nanoscale volumes and allow one to explain many experimental facts that did not have a coherent, logical justification. These include, for example, the formation of a “floating water bridge”, described in a number of works.
The essence of the experiment is that if two small chemical beakers with water are placed next to each other and platinum electrodes are lowered under them at a constant voltage of 15-30 kV, a water bridge with a diameter of 3 mm and a length of up to 25 mm is formed between the vessels. The bridge soars for a long time, has a layered structure, and water transfers from the anode to the cathode along it. This phenomenon and all its properties are a consequence of the presence of emulsions in water, which, apparently, have a dipole moment. One more property of the phenomenon can be predicted: at a water temperature above 75 ° C a “bridge” will not arise.
The anomalous properties of melt water are also easily explained. As noted in the literature, many of the properties of melt water — density, viscosity, electrical conductivity, refractive index, dissolving power, and others — differ from equilibrium parameters. Reducing these effects to the removal of deuterium from water as a result of a phase transition (melting point of “heavy ice” D 2 O 3.82 ° C) is not feasible, since the concentration of deuterium is extremely low - one atom of deuterium per 5-7 thousand hydrogen atoms.
The study of ice melting by acoustic emission made it possible for the first time to establish that, after complete melting of ice, melt water in a metastable state becomes a source of acoustic pulses, which serves as experimental confirmation of the formation of supramolecular complexes in water (Fig. 4).
Experiments show that melt water can remain in an active metastable state for almost 17 hours (after melting the ice, its microcrystals are preserved only for a split second and do not determine the properties of melt water at all). This mysterious phenomenon is explained by the fact that the destruction of the hexagonal crystal lattice of ice dramatically changes the structure of the substance. Ice crystals are destroyed faster than being converted to a stable equilibrium state the water formed from it.
The uniqueness of the ice-water phase transition lies in the fact that in melt water the concentration of hydrogen ions H + and hydroxyl OH - for a short time remains non-equilibrium, as it was in ice, i.e. a thousand times less than in ordinary water. After some time, the concentration of H + and OH - ions in water assumes its equilibrium value. Since hydrogen and hydroxyl ions play a decisive role in the formation of supramolecular complexes of water (emulsions), water remains in a metastable state for some time. The reaction of its dissociation H 2 O → H + + OH - requires a significant expenditure of energy and proceeds very slowly. The rate constant of this reaction is only 2.5 ∙ 10 –5 s –1 at 20 о С. Therefore, theoretically, the time of returning melt water to the equilibrium state should be 10-17 hours, which is observed in practice. Studies of the dynamics of changes in the concentration of hydrogen ions in melt water over time confirm this. Unusual properties of meltwater are the cause of talk about the "memory" of water. But by the “memory" of water should be understood the dependence of its properties on the background and nothing more. It is possible in different ways - freezing, heating, boiling, sonication, exposure to various fields, etc. - to transfer water to a metastable state, but it will be unstable, not retaining its properties for long. Optically, we found in melt water the presence of only one fraction of supramolecular formations with sizes of 1-3 microns. It is possible that a lower viscosity and a rarer spatial network of emulsions in melt water increase the dissolution capacity and diffusion rate.
The reality of the existence of emulons is confirmed by the classical method of thermal analysis (Fig. 5). The graph shows distinct peaks, indicating structural changes in the water. The most significant ones correspond to 36 ° C, the temperature of minimum heat capacity, 63 ° C, the temperature of minimum compressibility, and a peak at 75 ° C, the temperature of the maximum speed of sound in water, is especially characteristic. They can be interpreted as a kind of phase transitions associated with the destruction of emulsions. This allows us to conclude: liquid water is a very peculiar dispersed system, including at least five structural formations with various properties. Each structure exists in a specific temperature range characteristic of it. Exceeding the temperature above the threshold level critical for a given structure leads to its decay.
Literature
Zatsepina G. L. Physical properties and structure of water. - M .: Publishing house of Moscow University. - 1998 .-- 185 s.
Kuznetsov D. M., Gaponov V. L., Smirnov A. N. On the possibility of studying the kinetics of phase transitions in a liquid medium by acoustic emission // Engineering Physics, 2008, No. 1, p. 16-20.
Kuznetsov D.M., Smirnov A.N., Syroeshkin A.V. Acoustic emission during phase transformations in an aqueous medium // Russian Chemical Journal - M .: Ros. Chem. about them. D.I. Mendeleev, 2008, v. 52, No. 1, p. 114-121.
Smirnov A.N. Water structure: new experimental data. // Science and technology in industry, 2010, No. 4, p. 41-45.
Smirnov A.N. Acoustic emission during a chemical reaction and physicochemical processes // Russian Chemical Journal. - M.: ROS. Chem. about them. D.I. Mendeleev, 2001, v. 45, p. 29-34.
Smirnov A.N., Syroeshkin A.V. Supranadmolecular complexes of water // Russian Chemical Journal. - M.: ROS. Chem. about them. D.I. Mendeleev, 2004, v. 48, No. 2, p. 125-135.
Details for the curious
How does the "bridge" arise
The formation of the “water bridge” is described in the work of the Dutch physicist Elmar Fuchs and his colleagues.
Platinum electrodes are immersed in two small adjacent containers with water and a constant voltage of 15-20 kV is applied to them. In the photographs it is clearly seen that at first in the anode cup, and then in the cathode, on the surface of the water there are elevations that merge, forming a water bridge of circular cross section with a diameter of 2-4 mm between the containers. After this, the glasses can be moved one from another by 20-25 mm. The jumper has existed for quite some time, forming a “soaring water bridge”. Along the "bridge" flows water. The ends of the "bridge" are oppositely charged, so the water in the tanks acquires different pH values: 9 and 4. The "bridge" consists of thin streams; when you bring a charged glass rod to it, it splits into several sleeves. The high experimental technique made it possible to detect the movement of spherical formations on the surface of the “water bridge”.
