Water scientific definition. Physico-chemical properties of water

Whereas, most likely, you remember that for all other substances, their solid phase is heavier than the liquid phase.

Accordingly, it is good that ice is lighter than water - and this is also the main property of water that makes life in its current form possible.

Well, if this property of water did not exist, we would have to develop on the basis of, for example, ammonia. What a pleasure it is :)

Now let's focus on the fact that water can evaporate when boiling. But this is not the main property of water - since almost any substance evaporates when boiling, and there is nothing wrong with that. The important thing is that water evaporates both in a liquid state and even from the surface of ice. Why is this property more important than boiling evaporation? Here's why.

The fact that water can evaporate not only when boiling is the main property of water, since this makes it possible water cycle in nature. Which is definitely good, since water does not accumulate in one place, but is distributed more or less evenly throughout the planet. That is, roughly speaking, the Sahara Desert is not as hot and dry as it could be, because in Antarctica water evaporates from the surface of glaciers. Well, the oceans play an important role in this.

Accordingly, without the water cycle in nature, life would sit near a couple of oases, and the rest of the places would be an arid desert, where there is not a drop of moisture.

And therefore the property of water to evaporate is the main property of water.

Naturally, not only water can evaporate without boiling. Most aromatic compounds (alcohols, ethers, chloroform, etc.) do not evaporate when boiling. But water has one important advantage, another basic property - water is not toxic to living organisms. While alcohols and ethers are toxic. By the way, more about the toxicity (and how to deal with it) of ethyl alcohol, that is, vodka, in the article “Positive properties of structured vodka.”

Of course, in modern conditions, water can become toxic. But it's dealt with for water, and it's not such a big problem that it can't be dealt with.

So, another main property of water is that it is non-toxic.

Otherwise, we would, again, be different :)

And finally, the main property of water, which is important not only for life, but also for industry: water heats up quite slowly and cools down slowly (that is, can absorb a lot of heat). This property protects people and other animals, and the Earth, from overheating. And hypothermia. This is why living organisms can survive at -50 degrees Celsius and at + 50 degrees. If we were built on the basis of another substance, we would not be able to handle such a temperature range.

In addition, it must be taken into account that warm and cold water have different weights- warm water is lighter, cold water is heavier. Accordingly, water stratification occurs in the ocean - both in salinity and temperature. And in the ocean exactly the kind of life that is organized now is possible. Well, since we all came from the ocean, if it were not for this property of water, we would also be completely different.

And finally, the property of water to absorb heat and be on the surface in a heated state allows the existence of such things as warm currents - and in particular, the Gulf Stream. Which warms the whole of Europe, and without which in place of Europe there would be tundra with taiga, and not vineyards.

Perhaps you will name some other basic properties of water, but the ones listed above, in my opinion, are truly fundamental, since the existence of life on the planet depends on them exactly in the form in which life exists. I hope you find this information useful when you need to answer questions from curious children :)

And here is the promised presentation on the topic “Basic properties of water” for download: http://festival.1september.ru/articles/513123/

So, the basic properties of water are the properties thanks to which we are all alive!

And we have the look and shape that we have :)

other substances do not dissolve COMPLETELY in water

Water is the main component of all life on Earth. It is both the habitat of organisms and the main element in their structure, and, consequently, the source of life. It is used in all areas of industry. Therefore, it is very difficult to imagine life without water.

What is included in water

Everyone is well aware that water consists of hydrogen and oxygen. This is true. But in addition to these two elements, water also contains a huge list of chemical components.

What does water consist of?

It tends to transform, going through a hydrological cycle: evaporation, condensation and precipitation. During the course of these phenomena, water comes into contact with many organic compounds, metals, gases, as a result of which the liquid is supplemented with various elements.

The elements that make up water are divided into 6 categories:

1. Ions. These include: cations Na, K, Mg, Ca, anions: Cl, HCO 3 and SO 4. These components are found in water in the greatest quantities compared to others. They enter the liquid from soil layers, natural minerals, rocks, and also as elements of the decomposition of industrial products.
2. Dissolved gases: oxygen, nitrogen, hydrogen sulfide, carbon dioxide and others. The amount of each gas in water directly depends on its temperature.
3. Biogenic elements. The main ones are phosphorus and nitrogen, which enter the liquid from sediments, wastewater and agricultural waters.
4. Microelements. There are about 30 species. Their indicators in the composition of water are very small and range from 0.1 to micrograms per 1 liter. These include: bromine, selenium, copper, zinc, etc.
5. Organic substances dissolved in water and nitrogen-containing substances. These are alcohols, carbohydrates, aldehydes, phenols, peptides, etc.
6. Toxins. These are mainly heavy metals and petroleum products.

Water molecule

So, what molecules does water consist of?

The formula of water is trivial - H 2 O. And it shows that the water molecule consists of hydrogen and oxygen atoms. A stable connection has been established between them.

What does a water molecule look like in space? To determine the shape of a molecule, the centers of the atoms are connected with straight lines, resulting in a three-dimensional figure - a tetrahedron. This is the structure of water.

The shape of a water molecule can change depending on its state of aggregation. For the gaseous state, the angle between the oxygen and hydrogen atoms is 104.27 o, for the solid state - 109.5 o, for the liquid state - 105.03 o.

The molecules that make up water occupy a certain volume in space, while their shells are covered with an electron cloud in the form of a veil. The appearance of a water molecule, viewed in a plane, is compared to an X-shaped chromosome, which serves to transmit genetic information, and, therefore, gives rise to a new life. From this form an analogy is drawn between the chromosome and water as sources of life.

In space, a molecule looks like a three-dimensional triangle, a tetrahedron. This form is very stable and changes only due to the influence of external physical factors on the water.

What does water consist of? Of those atoms that are subject to the influence of van der Waals forces, the formation of hydrogen bonds. In this regard, random associates and clusters are formed between oxygen and hydrogen of neighboring molecules. The first are disordered structures, the second are ordered associates.

In the usual state of water, the number of associates is 60%, clusters - 40%.

The formation of hydrogen bridges is possible between neighboring water molecules, which contribute to the formation of various structures - clusters.

Clusters are able to interact with each other through hydrogen bonds, and this leads to the appearance of structures of a new order - hexahedrons.

Electronic structure of a water molecule

Atoms are what water is made of, and each atom has a different electronic structure. So, the graphical formula for electronic levels looks like this: 8 O 1s 2 2s 2 2p 4, 1 H 1s 1.

When the process of forming a water molecule occurs, an overlap of electron clouds occurs: two unpaired electrons of oxygen overlap with 1 unpaired electron of hydrogen. As a result of overlap, an angle of 104 degrees is formed between the atoms.

Physical state of water

As already mentioned, water molecules are dipoles, and this fact affects unusual One of these properties is that water can be present in nature in three states of aggregation: liquid, solid and vapor.

The transition from one state to another is due to the following processes:

1. Boiling - from liquid to vapor.
2. Condensation is the transition of their vapor into liquid (precipitation).
3. Crystallization is when a liquid turns into ice.
4. Melting is the process of melting ice and producing liquid.
5. Sublimation is the transformation of ice into a vapor state.
6. Desublimation is the reverse reaction of sublimation, that is, the transition of steam into ice.

The structure of its molecular lattice also depends on the state of water.

Conclusion

Thus, we can say that water has a simple structure, which can change depending on its condition. And it became clear to us what molecules water consists of.

Structural formula

True, empirical, or gross formula: H2O

Chemical composition of water

Molecular weight: 18.015

Water (hydrogen oxide) is a binary inorganic compound with the chemical formula H2O. A water molecule consists of two hydrogen atoms and one oxygen atom, which are connected by a covalent bond. Under normal conditions, it is a transparent liquid, colorless (in small volumes), odor and taste. In the solid state it is called ice (ice crystals can form snow or frost), and in the gaseous state it is called water vapor. Water can also exist in the form of liquid crystals (on hydrophilic surfaces). It makes up approximately 0.05% of the Earth's mass.

It is a good highly polar solvent. Under natural conditions, it always contains dissolved substances (salts, gases).

Water under normal conditions is in a liquid state, while similar hydrogen compounds of other elements are gases (H 2 S, CH 4, HF). The hydrogen atoms are attached to the oxygen atom, forming an angle of 104.45° (104°27′). Due to the large difference in electronegativity between hydrogen and oxygen atoms, the electron clouds are strongly biased towards oxygen. For this reason, the water molecule has a large dipole moment (p = 1.84 D, second only to hydrocyanic acid). Each water molecule forms up to four hydrogen bonds - two of them are formed by an oxygen atom and two by hydrogen atoms. The number of hydrogen bonds and their branched structure determine the high boiling point of water and its specific heat of vaporization. If there were no hydrogen bonds, water, based on the place of oxygen in the periodic table and the boiling points of hydrides of oxygen-like elements (sulfur, selenium, tellurium), would boil at −80 °C and freeze at −100 °C.

When transitioning to a solid state, water molecules are ordered, while the volumes of voids between the molecules increase, and the overall density of water decreases, which explains the lower density (larger volume) of water in the ice phase. During evaporation, on the contrary, all hydrogen bonds are broken. Breaking bonds requires a lot of energy, which is why water has the highest specific heat of any liquid or solid. In order to heat one liter of water by one degree, 4.1868 kJ of energy is required. Due to this property, water is often used as a coolant. In addition to its high specific heat capacity, water also has high specific heats of fusion (333.55 kJ/kg at 0 °C) and vaporization (2250 kJ/kg).

Strictly speaking, in this material we will briefly consider not only chemical and physical properties of liquid water, but also the properties inherent in it in general as such.

You can find out more about the properties of water in the solid state in the article - PROPERTIES OF WATER IN THE SOLID STATE (read →).

Water is a super-important substance for our planet. Without it, life on Earth is impossible; without it, not a single geological process takes place. The great scientist and thinker Vladimir Ivanovich Vernadsky wrote in his works that there is no such component whose significance could “be compared with it in its influence on the course of the main, most formidable geological processes.” Water is present not only in the body of all living creatures on our planet, but also in all substances on Earth - in minerals, in rocks... The study of the unique properties of water constantly reveals to us more and more new secrets, asks us new riddles and poses new challenges.

Anomalous properties of water

Many physical and chemical properties of water surprise and fall out of general rules and patterns and are anomalous, for example:

• In accordance with the laws established by the principle of similarity, within the framework of sciences such as chemistry and physics, we could expect that:
  • water will boil at minus 70°C and freeze at minus 90°C;
  • the water will not drip from the tip of the tap, but will flow in a thin stream;
  • the ice will sink rather than float on the surface;
  • more than a few grains of sugar would not dissolve in a glass of water.
• The surface of water has a negative electrical potential;
• When heated from 0°C to 4°C (3.98°C to be exact), water contracts;
• The high heat capacity of liquid water is surprising;

As noted above, in this material we will list the main physical and chemical properties of water and make brief comments on some of them.

Physical properties of water

PHYSICAL PROPERTIES are properties that appear outside of chemical reactions.

Water purity

The purity of water depends on the presence of impurities, bacteria, salts of heavy metals in it..., to familiarize yourself with the interpretation of the term PURE WATER according to our website, you need to read the article PURE WATER (read →).

Water color

The color of water depends on the chemical composition and mechanical impurities

As an example, let us give the definition of “Color of the Sea” given by the Great Soviet Encyclopedia.

The color of the sea. The color perceived by the eye when an observer looks at the surface of the sea. The color of the sea depends on the color of sea water, the color of the sky, the number and nature of clouds, the height of the Sun above the horizon, and other reasons.

The concept of the color of the sea should be distinguished from the concept of the color of sea water. Seawater color refers to the color perceived by the eye when viewing seawater vertically above a white background. Only a small part of the light rays incident on it is reflected from the surface of the sea, the rest of them penetrates into the depths, where they are absorbed and scattered by water molecules, suspended particles and tiny gas bubbles. The scattered rays reflected and emerging from the sea create the color spectrum. Water molecules scatter blue and green rays the most. Suspended particles scatter all rays almost equally. Therefore, sea water with a small amount of suspended matter appears blue-green (the color of the open parts of the oceans), and with a significant amount of suspended matter it appears yellowish-green (for example, the Baltic Sea). The theoretical side of the doctrine of central mathematics was developed by V. V. Shuleikin and C. V. Raman.

Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978

The smell of water

Odor of water – clean water usually has no odor.

Water clarity

The transparency of water depends on the minerals dissolved in it and the content of mechanical impurities, organic substances and colloids:

WATER TRANSPARENCY is the ability of water to transmit light. Usually measured by a Secchi disk. Depends mainly on the concentration of suspended and dissolved organic and inorganic substances in water. It can sharply decrease as a result of anthropogenic pollution and eutrophication of water bodies.

Ecological encyclopedic dictionary. - Chisinau I.I. Dedu. 1989

WATER TRANSPARENCY is the ability of water to transmit light rays. Depends on the thickness of the layer of water traversed by the rays, the presence of suspended impurities, dissolved substances, etc. In water, red and yellow rays are absorbed more strongly, and violet rays penetrate deeper. According to the degree of transparency, in order of decreasing it, waters are distinguished:

• transparent;
• slightly opalescent;
• opalescent;
• slightly cloudy;
• cloudy;
• very cloudy.

Dictionary of hydrogeology and engineering geology. - M.: Gostoptekhizdat. 1961

Taste of water

The taste of water depends on the composition of the substances dissolved in it.

Dictionary of hydrogeology and engineering geology

The taste of water is a property of water that depends on the salts and gases dissolved in it. There are tables of the palatable concentration of salts dissolved in water (in mg/l), for example the following table (according to Staff).

Water temperature

Melting point of water:

MELTING POINT - the temperature at which a substance changes from SOLID to liquid. The melting point of a solid is equal to the freezing point of a liquid, for example, the melting point of ice, O °C, is equal to the freezing point of water.

Boiling point of water : 99.974°C

Scientific and technical encyclopedic dictionary

BOILING POINT, the temperature at which a substance passes from one state (phase) to another, that is, from liquid to vapor or gas. The boiling point increases with increasing external pressure and decreases with decreasing pressure. It is usually measured at a standard pressure of 1 atmosphere (760 mm Hg). The boiling point of water at standard pressure is 100 °C.

Scientific and technical encyclopedic dictionary.

Triple point of water

Triple point of water: 0.01 °C, 611.73 Pa;

Scientific and technical encyclopedic dictionary

TRIPLE POINT, temperature and pressure at which all three states of matter (solid, liquid, gas) can exist simultaneously. For water, the triple point is located at a temperature of 273.16 K and a pressure of 610 Pa.

Scientific and technical encyclopedic dictionary.

Surface tension of water

Surface tension of water - determines the strength of adhesion of water molecules to each other, for example, how this or that water is absorbed by the human body depends on this parameter.

Water hardness

Marine dictionary

WATER HARDNESS (Stiffness of Water) - a property of water that is exsanguinated by the content of alkaline earth metal salts dissolved in it, ch. arr. calcium and magnesium (in the form of bicarbonate salts - bicarbonates), and salts of strong mineral acids - sulfuric and hydrochloric. L.V. is measured in special units, the so-called. degrees of hardness. The degree of hardness is the weight content of calcium oxide (CaO), equal to 0.01 g in 1 liter of water. Hard water is unsuitable for feeding boilers, as it promotes strong scale formation on their walls, which can cause burnout of the boiler tubes. Boilers of high power and especially high pressure must be fed with completely purified water (condensate from steam engines and turbines, purified by filters from oil impurities, as well as distillate prepared in special evaporator apparatus).

Samoilov K.I. Marine dictionary. — M.-L.: State Naval Publishing House of the NKVMF of the USSR, 1941

Scientific and technical encyclopedic dictionary

WATER HARDNESS, the inability of water to form foam with soap due to salts dissolved in it, mainly calcium and magnesium.

Scale in boilers and pipes is formed due to the presence of dissolved calcium carbonate in the water, which enters the water upon contact with limestone. In hot or boiling water, calcium carbonate precipitates as hard limescale deposits on surfaces inside boilers. Calcium carbonate also prevents soap from foaming. The ion exchange container (3) is filled with granules coated with sodium-containing materials. with which water comes into contact. Sodium ions, being more active, replace calcium ions. Since sodium salts remain soluble even when boiled, scale does not form.

Scientific and technical encyclopedic dictionary.

Water structure

Water mineralization

Water mineralization :

Ecological encyclopedic dictionary

WATER MINERALIZATION - saturation of water with inorganic. (mineral) substances found in it in the form of ions and colloids; the total amount of inorganic salts contained mainly in fresh water, the degree of mineralization is usually expressed in mg/l or g/l (sometimes in g/kg).

Ecological encyclopedic dictionary. - Chisinau: Main editorial office of the Moldavian Soviet Encyclopedia. I.I. Dedu. 1989

Water viscosity

Water viscosity characterizes the internal resistance of liquid particles to its movement:

Geological Dictionary

The viscosity of water (liquid) is a property of a liquid that causes the occurrence of friction force during movement. It is a factor that transfers motion from layers of water moving at high speed to layers at lower speed. V. in. depends on the temperature and concentration of the solution. Physically, it is estimated by coefficient. viscosity, which is included in a number of formulas for the movement of water.

Geological Dictionary: in 2 volumes. - M.: Nedra. Edited by K. N. Paffengoltz et al. 1978

There are two types of water viscosity:

• Dynamic viscosity of water is 0.00101 Pa s (at 20°C).

• Kinematic viscosity of water is 0.01012 cm 2 /s (at 20°C).

Critical point of water

The critical point of water is its state at a certain ratio of pressure and temperature, when its properties are the same in the gaseous and liquid states (gaseous and liquid phases).

Critical point of water: 374°C, 22.064 MPa.

Dielectric constant of water

Dielectric constant, in general, is a coefficient indicating how much the force of interaction between two charges in a vacuum is greater than in a certain environment.

In the case of water, this figure is unusually high and for static electric fields it is 81.

Heat capacity of water

Heat capacity of water - water has a surprisingly high heat capacity:

Ecological dictionary

Heat capacity is the property of substances to absorb heat. It is expressed as the amount of heat absorbed by a substance when it is heated by 1°C. The heat capacity of water is about 1 cal/g, or 4.2 J/g. The heat capacity of the soil (at 14.5-15.5 ° C) ranges (from sandy to peat soils) from 0.5 to 0.6 cal (or 2.1-2.5 J) per unit volume and from 0.2 up to 0.5 cal (or 0.8-2.1 J) per unit mass (g).

Ecological Dictionary. - Alma-Ata: “Science”. B.A. Bykov. 1983

Scientific and technical encyclopedic dictionary

SPECIFIC HEAT CAPACITY (symbol c), the heat required to raise the temperature of 1 kg of a substance by 1 K. It is measured in J/K.kg (where J is JOUL). Substances with a high specific heat, such as water, require more energy to raise their temperature than substances with a low specific heat.

Scientific and technical encyclopedic dictionary.

Thermal conductivity of water

Thermal conductivity of a substance implies its ability to conduct heat from its hotter parts to its colder parts.

Heat transfer in water occurs either at the molecular level, i.e., transferred by water molecules, or due to the movement / movement of any volumes of water - turbulent thermal conductivity.

The thermal conductivity of water depends on temperature and pressure.

Fluidity of water

The fluidity of substances is understood as their ability to change their shape under the influence of constant stress or constant pressure.

The fluidity of liquids is also determined by the mobility of their particles, which at rest are unable to perceive shear stress.

Water inductance

Inductance determines the magnetic properties of closed electric current circuits. Water, with the exception of some cases, conducts electric current, and therefore has a certain inductance.

Density of water

The density of water is determined by the ratio of its mass to volume at a certain temperature. Read more in our material - WHAT IS WATER DENSITY(read →).

Compressibility of water

The compressibility of water is insignificant and depends on the salinity of the water and pressure. For example, for distilled water it is 0.0000490.

Electrical conductivity of water

The electrical conductivity of water largely depends on the amount of salts dissolved in it.

Radioactivity of water

The radioactivity of water depends on the content of radon in it, the emanation of radium.

Physico-chemical properties of water

Dictionary of hydrogeology and engineering geology

PHYSICAL AND CHEMICAL PROPERTIES OF WATER - parameters that determine the physical and chemical characteristics of natural waters. These include indicators of the concentration of hydrogen ions (pH) and oxidation-reduction potential (Eh).

Dictionary of hydrogeology and engineering geology. - M.: Gostoptekhizdat. Compiled by A. A. Makkaveev, editor O. K. Lange. 1961

Acid-base balance of water

Redox potential of water

The oxidation-reduction potential of water (ORP) is the ability of water to enter into biochemical reactions.

Chemical properties of water

CHEMICAL PROPERTIES OF A SUBSTANCE are properties that appear as a result of chemical reactions.

Below are the chemical properties of water according to the textbook “Fundamentals of Chemistry. Internet textbook” by A. V. Manuilova, V. I. Rodionov.

Interaction of water with metals

When water interacts with most metals, a reaction occurs that releases hydrogen:

• 2Na + 2H2O = H2 + 2NaOH (boisterous);
• 2K + 2H2O = H2 + 2KOH (boil);
• 3Fe + 4H2O = 4H2 + Fe3O4 (only when heated).

Not all, but only sufficiently active metals can participate in redox reactions of this type. Alkali and alkaline earth metals of groups I and II react most easily.

Interaction of water with non-metals

Non-metals that react with water include, for example, carbon and its hydrogen compound (methane). These substances are much less active than metals, but are still capable of reacting with water at high temperatures:

• C + H2O = H2 + CO (high heat);
• CH4 + 2H2O = 4H2 + CO2 (at high heat).

Interaction of water with electric current

When exposed to electric current, water decomposes into hydrogen and oxygen. This is also a redox reaction, where water is both an oxidizing agent and a reducing agent.

Interaction of water with non-metal oxides

Water reacts with many non-metal oxides and some metal oxides. These are not redox reactions, but coupling reactions:

SO2 + H2O = H2SO3 (sulfurous acid)

SO3 + H2O = H2SO4 (sulfuric acid)

CO2 + H2O = H2CO3 (carbonic acid)

Interaction of water with metal oxides

Some metal oxides can also react with water. We have already seen examples of such reactions:

CaO + H2O = Ca(OH)2 (calcium hydroxide (slaked lime)

Not all metal oxides are capable of reacting with water. Some of them are practically insoluble in water and therefore do not react with water. For example: ZnO, TiO2, Cr2O3, from which, for example, water-resistant paints are prepared. Iron oxides are also insoluble in water and do not react with it.

Hydrates and crystalline hydrates

Water forms compounds, hydrates and crystalline hydrates, in which the water molecule is completely preserved.

For example:

• CuSO4 + 5 H2O = CuSO4.5H2O;
• CuSO4 is a white substance (anhydrous copper sulfate);
• CuSO4.5H2O - crystalline hydrate (copper sulfate), blue crystals.

Other examples of hydrate formation:

• H2SO4 + H2O = H2SO4.H2O (sulfuric acid hydrate);
• NaOH + H2O = NaOH.H2O (caustic soda hydrate).

Compounds that bind water into hydrates and crystalline hydrates are used as desiccants. With their help, for example, water vapor is removed from humid atmospheric air.

Biosynthesis

Water participates in bio-synthesis as a result of which oxygen is formed:

6n CO 2 + 5n H 2 O = (C 6 H 10 O 5) n + 6n O 2 (under light)

We see that the properties of water are diverse and cover almost all aspects of life on Earth. As one of the scientists formulated ... it is necessary to study water comprehensively, and not in the context of its individual manifestations.

When preparing the material, information was used from the books - Yu. P. Rassadkin “Ordinary and Extraordinary Water”, Yu. Ya. Fialkov “Unusual Properties of Ordinary Solutions”, Textbook “Fundamentals of Chemistry. Internet textbook” by A. V. Manuilova, V. I. Rodionov and others.

History of discovery

Heavy hydrogen water molecules were first discovered in natural water by Harold Urey in 1932, for which the scientist was awarded the Nobel Prize in Chemistry in 1934. And already in 1933, Gilbert Lewis isolated pure heavy hydrogen water. During the electrolysis of ordinary water, which contains, along with ordinary water molecules, a small amount of heavy (D 2 O) and semi-heavy (HDO) water molecules formed by the heavy hydrogen isotope, the residue is gradually enriched with molecules of these compounds. From such a residue, after repeating electrolysis many times, Lewis in 1933 was the first to isolate a small amount of water, consisting almost 100% of molecules of an oxygen compound with deuterium and called heavy. This method of producing heavy water remains the main one today, although it is used mainly at the final stage of enrichment from 5-10% to >99% (see below).

After the discovery of nuclear fission in late 1938 and the realization of the possibility of using neutron-induced nuclear fission chain reactions, the need arose for a neutron moderator - a substance that can effectively slow down neutrons without losing them in capture reactions. Neutrons are most effectively moderated by light nuclei, and the most effective moderator would be ordinary hydrogen (protium) nuclei, but they have a high neutron capture cross section. In contrast, heavy hydrogen captures very few neutrons (the thermal neutron capture cross section of protium is more than 100 thousand times higher than that of deuterium). Technically, the most convenient deuterium compound is heavy water, and it can also serve as a coolant, removing the generated heat from the area where the fission chain reaction occurs. Since the earliest times of nuclear power, heavy water has become an important component in some reactors, both for power generation and those designed to produce plutonium isotopes for nuclear weapons. These so-called heavy water reactors have the advantage that they can operate on natural (unenriched) uranium without the use of graphite moderators, which during decommissioning can pose a dust explosion hazard and contain induced radioactivity (carbon-14 and a number of other radionuclides). However, most modern reactors use enriched uranium with normal "light water" as a moderator, despite the partial loss of moderated neutrons.

Production of heavy water in the USSR

Being in nature

In natural waters, there is one deuterium atom for every 6400-7600 protium atoms. Almost all of it is contained in DHO molecules, one such molecule accounts for 3200-3800 molecules of light water. Only a very small fraction of deuterium atoms form heavy water molecules D 2 O, since the probability of two deuterium atoms meeting in one molecule in nature is small (approximately 0.5⋅10 −7). With an artificial increase in the concentration of deuterium in water, this probability increases.

Biological role and physiological effects

Heavy water is only slightly toxic, chemical reactions in its environment are somewhat slower compared to ordinary water, and hydrogen bonds involving deuterium are somewhat stronger than usual. Experiments on mammals (mice, rats, dogs) have shown that replacing 25% of hydrogen in tissues with deuterium leads to sterility, sometimes irreversible. Higher concentrations lead to rapid death of the animal; Thus, mammals that drank heavy water for a week died when half the water in their bodies was deuterated; fish and invertebrates die only when the water in the body is 90% deuterated. Protozoa are able to adapt to a 70% solution of heavy water, and algae and bacteria are able to live even in clean heavy water. A person can drink several glasses of heavy water without any visible harm to health; all deuterium will be removed from the body in a few days. Thus, in one of the experiments to study the connection between the vestibular apparatus and involuntary eye movements (nystagmus), volunteers were asked to drink from 100 to 200 grams of heavy water; as a result of the absorption of denser heavy water by the cupula (a gelatinous structure in the semicircular canals), its neutral buoyancy in the endolymph of the canals is disrupted, and slight disturbances in spatial orientation occur, in particular nystagmus. This effect is similar to that which occurs when drinking alcohol (however, in the latter case, the density of the cupula decreases, since the density of ethyl alcohol is less than the density of water).

Thus, heavy water is much less toxic than, for example, table salt. Heavy water has been used to treat hypertension in humans in daily doses ranging from 10 to 675 g D 2 O per day.

The human body contains as a natural impurity the same amount of deuterium as 5 grams of heavy water; This deuterium is mainly found in HDO semi-heavy water molecules, as well as in all other biological compounds that contain hydrogen. [ ]

Some information

Heavy water accumulates in the electrolyte residue during repeated electrolysis of water. In the open air, heavy water quickly absorbs vapor from ordinary water, so we can say that it is hygroscopic. The production of heavy water is very energy intensive, so its cost is quite high. In 1935, immediately after the discovery of heavy water, its price was approximately $19 per gram. Currently, heavy water with a deuterium content of 99 at.%, sold by suppliers of chemical reagents, costs about 1 euro per gram when purchasing 1 kg, but this price refers to a product with controlled and guaranteed quality of the chemical reagent; with lower quality requirements, the price can be an order of magnitude lower.

Application

The most important property of heavy hydrogen water is that it practically does not absorb neutrons, therefore it is used in nuclear reactors to moderate neutrons and as a coolant. It is also used as an isotope indicator in chemistry, biology and hydrology, agricultural chemistry, etc. (including in experiments with living organisms and in diagnostic studies of humans). In particle physics, heavy water is used to detect neutrinos; Thus, the largest solar neutrino detector SNO (Canada) contains 1000 tons of heavy water.

Deuterium is a nuclear fuel for the energy sector of the future, based on controlled thermonuclear fusion. The first energy reactors of this type are expected to carry out the reaction D + T → 4 He + n + 17.6 MeV .

In some countries (for example, Australia), the commercial circulation of heavy water is subject to government restrictions, which is associated with the theoretical possibility of its use to create “unauthorized” natural uranium reactors suitable for producing weapons-grade plutonium.

Other types of heavy water

Semi-heavy water

Semi-heavy water is also distinguished (also known as deuterium water, monodeuterium water, deuterium hydroxide), in which only one hydrogen atom is replaced by deuterium. The formula of such water is written as follows: DHO or ²HHO. It should be noted that water, which has the formal composition of DHO, due to isotope exchange reactions, will actually consist of a mixture of DHO, D 2 O and H 2 O molecules (in a ratio of approximately 2: 1: 1). This point also applies to THO and TDO.

Super heavy water

Superheavy water contains tritium, which has a half-life of more than 12 years. According to its properties, superheavy water ( T2O) differs even more noticeably from the usual one: it boils at 104 °C, freezes at +9 °C and has a density of 1.21 g/cm³. All nine variants of superheavy water are known (that is, obtained in the form of more or less pure macroscopic samples): THO, TDO and T 2 O with each of the three stable isotopes of oxygen (16 O, 17 O and 18 O). Sometimes superheavy water is simply called heavy water if this does not cause confusion. Superheavy water has high radiotoxicity.

Heavy oxygen isotope modifications of water

Term heavy water also used in relation to heavy oxygen water, in which the usual light oxygen 16 O is replaced by one of the heavy stable isotopes 17 O or 18 O. Heavy oxygen isotopes exist in a natural mixture, therefore natural water always contains an admixture of both heavy oxygen modifications. Their physical properties are also somewhat different from those of ordinary water; Thus, the freezing point of 1 H 2 18 O is +0.28 °C.

Heavy oxygen water, in particular 1 H 2 18 O, is used in the diagnosis of oncological diseases (from it the fluorine-18 isotope is obtained on a cyclotron, which is used for the synthesis of drugs for the diagnosis of oncological diseases, in particular 18-fdg).

Total number of isotopic modifications of water

If you count all possible non-radioactive compounds with the general formula H 2 O, then the total number of possible isotopic modifications of water is only nine (since there are two stable isotopes of hydrogen and three of oxygen):

• H 2 16 O - light water, or just water
• H 2 17 O
• H 2 18 O - heavy oxygen water
• HD 16 O - semi-heavy water
• HD 17 O
• HD 18 O
• D 2 16 O - heavy water
• D 2 17 O
• D 2 18 O

Taking tritium into account, their number increases to 18:

• T 2 16 O - superheavy water
• T 2 17 O
• T 2 18 O
• DT 16 O
• DT 17 O
• DT 18 O
• HT 16 O
• HT 17 O
• HT 18 O

Thus, except common, most common in nature "light" water 1 H 2 16 O, there are a total of 8 non-radioactive (stable) and 9 radioactive “heavy waters”.