The famous Soviet scientist academician I. V. Petryanov called his popular science book about water “The most unusual substance in the world".
And Doctor of Biological Sciences B. F. Sergeev began his book "Entertaining Physiology" with a chapter about water – "The Substance that created our planet".
The scientists are right: there is no substance on Earth more important for us than ordinary water, and at the same time there is no other such substance in the properties of which there would be as many contradictions and anomalies as in its properties.
Almost three quarters of the surface of our planet is occupied by oceans and seas.
Solid water – snow and ice covers 20% of the land.
Of the total amount of water on Earth, equal to 1 billion 386 million cubic kilometers, 1 billion 338 million cubic kilometers account for the salt waters of the World Ocean, and only 35 million cubic kilometers account for fresh water.
The total amount of ocean water would be enough to cover the globe with a layer of more than 2.5 kilometers.
For every inhabitant of the Earth, there are approximately 0.33 cubic kilometers of sea water and 0.008 cubic kilometers of fresh water.
But the difficulty is that the vast majority of fresh water on Earth is in a state that makes it difficult for humans to access.
Almost 70% of fresh water is contained in the ice sheets of the polar countries and in mountain glaciers, 30% - in aquifers underground, and only 0.006% of fresh water is contained simultaneously in the beds of all rivers.
Water molecules have been detected in interstellar space.
Water is a part of comets, most of the planets of the solar system and their satellites.
The isotopic composition.
There are nine stable isotopic varieties of water.
Their content in fresh water is on average the following: ^1 N 2 ^16 O – 99.73%, ^1 N 2 ^18 O – 0.2%,
^1 H 2 ^ 17 O – 0.04%, ^1 H^2 H^16 O – 0.03%.
The remaining five isotopic varieties are present in water in negligible amounts.
The structure of the molecule.
As is known, the properties of chemical compounds depend on what elements their molecules consist of, and change naturally.
Water can be considered as hydrogen oxide or as oxygen hydride.
The hydrogen and oxygen atoms in the water molecule are located in the corners of an isosceles triangle with an O – H bond length of 0.957 nm; the valence angle of H – O – H is 104^o 27^’ .
*104^0 27^' *
But since both hydrogen atoms are located on the same side of the oxygen atom, the electric charges in it are dispersed.
The water molecule is polar, which is the reason for the special interaction between its different molecules.
The hydrogen atoms in the water molecule, having a partial positive charge, interact with the electrons of the oxygen atoms of neighboring molecules.
Such a chemical bond is called *v o d o r o d n o y* .
It combines water molecules into a kind of polymers of spatial structure.
About 1% of water dimers are present in water vapor.
The distance between oxygen atoms is 0.3 nm.
In the liquid and solid phases, each water molecule forms four hydrogen bonds: two as a proton donor and two as a proton acceptor.
The average length of these bonds is 0, 28 nm, the H – O – H angle tends to 180^0 .
The four hydrogen bonds of the water molecule are directed approximately to the vertices of a regular tetrahedron.
The structure of ice modifications is a three dimensional grid.
In the modifications existing at low pressures, the so called ice I, the H – O – H bonds are almost straight and directed to the vertices of a regular tetrahedron.
But at high pressures, ordinary ice can be turned into so – called ice – II, ice – III, and so on heavier and denser crystalline forms of this substance.
The hardest, densest and most refractory so far are ice VII and ice VIII.
Ice VII was obtained under a pressure of 3 billion Pa, it melts at a temperature of + 190^0 C .
In the modifications ice II ice VI c, the H – O – H bonds are curved and the angles between them differ from the tetrahedral, which causes an increase in density compared to the density of ordinary ice.
Only in the ice – VII and ice – VIII modifications, the highest packing density is achieved: in their structure, two regular grids built of tetrahedra are inserted into one another, while the system of rectilinear hydrogen bonds is preserved.
A three dimensional grid of hydrogen bonds constructed from tetrahedra also exists in liquid water in the entire range from the melting point to the critical temperature equal to + 3.98^0 C.
The increase in density during melting, as in the case of dense modifications of ice, is explained by the curvature of hydrogen bonds.
The curvature of hydrogen bonds increases with increasing temperature and pressure, which leads to an increase in density.
On the other hand, when heated, the average length of hydrogen bonds becomes longer, as a result of which the density decreases.
The combined effect of the two facts explains the presence of a maximum density of water at a temperature of + 3.98^0 C.
* The physical properties* of water are abnormal, which is explained by the above data on the interaction between water molecules.
Water is the only substance on Earth that exists in nature in all three aggregate states liquid, solid and gaseous.
Melting of ice at atmospheric pressure is accompanied by a decrease in volume by 9%.
The density of liquid water at a temperature close to zero is greater than that of ice.
At 0^0 S, 1 gram of ice occupies a volume of 1,0905 cubic centimeters, and 1 gram of liquid water occupies a volume of 1,0001 cubic centimeters.
And the ice floats, that's why reservoirs usually do not freeze through, but are only covered with an ice cover.
The temperature coefficient of volumetric expansion of ice and liquid water is negative at temperatures below - 210^0 C and + 3.98^0 C, respectively.
The heat capacity during melting increases almost twice and in the range from 0^0 S to 100^0 S almost does not depend on the temperature.
Water has disproportionately high melting and boiling points in comparison with other hydrogen compounds of elements of the main subgroup of group VI of the periodic table.
*telluride hydrogen selenium hydrogen sulfide water*
*N* *_2 * *Te* *N* *_2 * *S* *e* *N* *_2 * *S* *N 2 O*
*_____________________________________________________*
* Melting point * * - 51^0 S 64^0 S 82^0 S 0^0 S *
*_____________________________________________________*
* Boiling point 4^0 S 42^0 S - 61^0 S 100^0 S *
*_____________________________________________________*
It is necessary to bring additional energy to loosen and then destroy the hydrogen bonds.
And this energy is very significant.
That is why the heat capacity of water is so great.
Thanks to this feature, water forms the climate of the planet.
Geophysicists claim that the Earth would have cooled down long ago and turned into a lifeless piece of stone, if not for water.
Heating up, it absorbs heat, cooling down, gives it away.
Earth's water both absorbs and returns a lot of heat, and thereby "evens out" the climate.
The formation of the climate of the continents is especially noticeably influenced by sea currents, which form closed circulation rings in each ocean.
The most striking example is the influence of the Gulf Stream, a powerful system of warm currents running from the Florida Peninsula in North America to Svalbard and Novaya Zemlya.
Thanks to the Gulf Stream, the average January temperature on the coast of Northern Norway, beyond the Arctic Circle, is the same as in the steppe part of the Crimea about 0^0 C, i.e. increased by 15-20^0 C.
And in Yakutia at the same latitude, but far from the Gulf Stream – minus 40^0 S.
And the Earth is protected from the cosmic cold by those water molecules that are scattered in the atmosphere – in clouds and in the form of vapors.
Water vapor creates a powerful "greenhouse effect", which delays up to 60% of the thermal radiation of our planet, does not allow it to cool down.
According to the calculations of M. I. Budyko, if the water vapor content in the atmosphere was halved, the average temperature of the Earth's surface would decrease by more than 5^0 C (from 14.3 to 9^0 C).
The huge values of the latent heat of melting and evaporation of water have a noticeable effect on the mitigation of the Earth's climate, in particular on the equalization of air temperature in the transitional seasons – spring and autumn.
But this is not the only reason why we consider water to be a vital substance.
The fact is that the human body consists of almost 63-68% water.
Almost all biochemical reactions in every living cell are reactions in aqueous solutions.
With water, toxic slags are removed from our body; the water released by the sweat glands and evaporating from the surface of the skin regulates the temperature of our body.
Representatives of the animal and plant world contain the same abundance of water in their organisms.
The least water, only 5-7% of the weight, contains some mosses and lichens.
Most of the inhabitants of the globe and plants consist of more than half of water.
For example, mammals contain 60-68 %; fish – 70 %; algae – 90-98% of water.
In solutions (mainly water), most technological processes take place at chemical industry enterprises, in the production of medicines and food products.
It is no accident that hydrometallurgy – the extraction of metals from ores and concentrates using solutions of various reagents has become an important industry.
Water is an important source of energy resources.
As you know, all hydroelectric power plants in the world, from the smallest to the largest, convert the mechanical energy of the water flow into electrical energy exclusively with the help of water turbines with electric generators connected to them.
In nuclear power plants, a nuclear reactor heats water, water vapor turns a turbine with a generator and generates an electric current.
Water, despite all its anomalous properties, is a standard for measuring the temperature, mass ( weight), amount of heat, height of the terrain.
Swedish physicist Anders Celsius, a member of the Stockholm Academy of Sciences, created a centigrade thermometer scale in 1742, which is now used almost everywhere.
The boiling point of water is indicated by 100, and the melting point of ice is 0 .
When developing the metric system, established by a decree of the French revolutionary government in 1793, instead of various ancient measures, water was used to create the main measure of mass – weight) - a kilogram and a gram: 1 gram, as is known, is the weight of 1 cubic centimeter (milliliter) of pure water at the temperature of its highest density – 4^0 C.
Therefore, 1 kilogram is the weight of 1 liter (1000 cubic centimeters) or 1 cubic decimeter of water: and 1 ton (1000 kilograms) is the weight of 1 cubic meter of water.
Water is also used to measure the amount of heat.
One calorie is the amount of heat needed to heat 1 gram of water from 14.5 to 15.5^0 C.
All heights and depths on the globe are counted from sea level.
In 1932, the Americans G. Urey and E. Osborn discovered that even the purest water that can only be obtained under laboratory conditions contains an insignificant amount of some substance, apparently expressed by the same chemical formula H 2 O, but having a molecular weight of 20 instead of the weight of 18 inherent in ordinary water.
Yuri called this substance heavy water.
The large weight of heavy water is explained by the fact that its molecules consist of hydrogen atoms with twice the atomic weight esom compared to the atoms of ordinary hydrogen.
The double weight of these atoms, in turn, is due to the fact that their nuclei contain, in addition to the single proton that makes up the nucleus of ordinary hydrogen, another neutron.
The heavy isotope of hydrogen is called deuterium
(D or ^2 N), and ordinary hydrogen was called protium.
Heavy water, deuterium oxide, is expressed by the formula D 2 O.
Soon a third, superheavy isotope of hydrogen with one proton and two neutrons in the nucleus was discovered, which was called tritium (T or ^3 N).
In combination with oxygen, tritium forms superheavy water T 2 O with a molecular weight of 22.
On average, about 0.016% of heavy water is contained in natural waters.
Heavy water looks similar to ordinary water, but differs from it in many physical properties.
The boiling point of heavy water is 101.4^0 C, the freezing point is + 3.8^0 C. Heavy water is 11% heavier than normal.
The specific gravity of heavy water at a temperature of 25 ^ 0 C is 1.1.
It is worse ( by 5 – 15% ) dissolves various salts.
In heavy water, the rate of some chemical reactions is different than in ordinary water.
And in physiological terms, heavy water affects living matter differently: unlike ordinary water, which has a life giving power, heavy water is completely inert.
Plant seeds, if watered with heavy water, do not germinate; tadpoles, microbes, worms, fish cannot exist in heavy water; if animals are watered with heavy water alone, they will die of thirst.
Heavy water is dead water.
There is another type of water that differs in physical properties from ordinary water - this is magnetized water.
Such water is obtained using magnets mounted in a pipeline through which water flows.
The magnetized water changes its physical and chemical properties: the rate of chemical reactions in it increases, the crystallization of dissolved substances accelerates, the adhesion of solid particles of impurities increases and their precipitation with the formation of large flakes (coagulation).
Omagnetization is successfully used at water supply stations with a large turbidity of the water taken away.
It also allows you to quickly precipitate polluted industrial effluents.
Of the* chemical properties * of water, the ability of its molecules to dissociate (break up) into ions and the ability of water to dissolve substances of different chemical nature are especially important.
The role of water as the main and universal solvent is determined primarily by the polarity of its molecules and, as a result, its extremely high dielectric constant.
Dissimilar electric charges, and in particular ions, are attracted to each other in water 80 times weaker than they would be attracted in air.
The forces of mutual attraction between molecules or atoms of a body immersed in water are also weaker than in air.
In this case, it is easier for the thermal movement to break up the molecules.
That is why the dissolution occurs, including many difficult to dissolve substances: a drop sharpens a stone.
Only a small fraction of the molecules (one in 500,000,000) undergoes electrolytic dissociation according to the scheme:
N 2 O N^+ + HE^-
However, the above equation is conditional: a proton H^+ devoid of an electron shell cannot exist in an aqueous medium .
It immediately combines with a water molecule, forming a hydroxonium ion H 3 O^+, which in turn combines with one, two or three water molecules in
N 3 O^+, N 5 O 2 ^+, N 7 O 3 ^+ .
Electrolytic dissociation of water is the cause of hydrolysis of salts of weak acids and (or) bases.
The degree of electrolytic dissociation increases markedly with increasing temperature.
Formation of water from the elements by reaction:
N 2 + ^1 /_2 O 2 N 2 O -242 kJ/mol for steam
-286 kJ/mol for liquid water
-at low temperatures, in the absence of catalysts, it occurs extremely slowly, but the reaction rate increases sharply with increasing temperature, and at 550^0 C it occurs with an explosion.
When the pressure decreases and the temperature increases, the equilibrium shifts to the left.
Under the influence of ultraviolet radiation, photodissociation of water into H^+ and OH^ - ions occurs .
Ionizing radiation causes radiolysis of water with the formation of H 2 ; N 2 O 2 and free radicals: N^* ; HE^*; O^* .
Water is a reactive compound.
Water is oxidized by atomic oxygen:
N 2 O + O N 2 O 2
When interacting with F 2, HF is formed, as well as O 2 ;O 3 ; N 2 O 2 ; F 2 O and other connections.
Water reacts with the remaining halogens at low temperatures to form a mixture of H Gal and H Gal O acids.
Under normal conditions, up to half of the SI 2 dissolved in it and significantly smaller amounts of Br 2 and J _2 interact with water .
At elevated temperatures, CI 2 and Br 2 decompose water to form H Gal and O 2 .
When water vapor passes through hot coal, it decomposes and the so called water gas is formed:
H 2 O + C CO + H 2
At an elevated temperature in the presence of a catalyst, water reacts with CO; CH 4 and other hydrocarbons, for example:
H 2 O + CO CO 2 + H 2
H 2 O + CH 4 CO + 3H 2
These reactions are used for the industrial production of hydrogen.
Phosphorus is oxidized to metaphosphoric acid when heated with water under pressure in the presence of a catalyst:
6N 2 O + 3R 2NRO 3 + 5N 2
Water interacts with many metals to form H 2 and the corresponding hydroxide.
With alkaline and alkaline earth metals (except Md ) this reaction takes place already at room temperature.
Less active metals decompose water at an elevated temperature, for example, Md and Zn above 100 ^ 0 C; Fe above 600^0 C :
2Fe + 3H 2 O Fe 2 O _3 + 3H 2
When many oxides react with water, acids or bases are formed.
Water can serve as a catalyst, for example, alkali metals and hydrogen react with CI 2 only in the presence of traces of water.
Sometimes water is a catalytic poison, for example, for an iron catalyst in the synthesis of NH 3 .
The ability of water molecules to form three dimensional networks of hydrogen bonds allows it to give gas hydrates with inert gases, hydrocarbons, CO 2, CI 2, (CH 2 )_2 O, CHCI 3 and many other substances.
Until about the end of the 19th century, water was considered a free inexhaustible gift of nature.
It was not enough only in sparsely populated areas of deserts.
In the 20th century, the view of water changed dramatically.
As a result of the rapid growth of the world's population and the rapid development of industry, the problem of supplying humanity with clean fresh water has become almost the world's number one problem.
Currently, people use about 3,000 billion cubic meters of water annually, and this figure is constantly growing rapidly.
In many densely populated industrial areas, clean water is no longer enough.
The lack of fresh water on the globe can be made up in various ways: desalinate seawater, and replace it with fresh water, where possible in technology; purify wastewater to such an extent that it can be safely lowered into reservoirs and watercourses, without fear of polluting, and use it again; economically consume fresh water, creating a less water intensive production technology, replacing, where possible, high quality fresh water with lower quality water, etc.
V O d A - o d n o i z g l a v n y x b o g a t s t v h e l o v e h e s t v a n a z e m l e .
*S P I S O K L I T E R A T U R S :*
1.
Chemical Encyclopedia.
Volume 1.
Editor I. L. Knunyants.
Moscow, 1988.
2. Encyclopedic dictionary of a young chemist.
Compilers
V. A. Kritsman, V. V. Stanzo.
Moscow, " Pedagogy“, 1982god.
3. The word about water.
Author O. A. Spangler.
Leningrad,
"Hydrometeoizdat", 1980.
4. The most unusual substance in the world.
Author
I. V. Petryanov.
Moscow, " Pedagogy“, 1975.
P L A N .
I. Introduction.
Statements of famous scientists about water.
*II* *.
The main part.
*  1. The distribution of water on the planet Earth, in the outer space
space.
2. The isotopic composition of water.
3. The structure of the water molecule.
4. Physical properties of water, their anomaly.
a).Aggregate states of water.
b).The density of water in the solid and liquid state.
c).The heat capacity of water.
d).Melting and boiling points of water in comparison with
other hydrogen compounds of the elements
the main subgroup YI of the group of the periodic table.
5. The influence of water on the formation of the climate on the planet
Earth.
6. Water as the main component of plant and animal products
animal organisms.
7. The use of water in industry, production
electricity supply.
8. Using water as a reference.
a).To measure the temperature.
b).To measure the mass (weight).
c).To measure the amount of heat.
d).To measure the height of the terrain.
9. Heavy water, its properties.
10. Magnetized water, its properties.
11. Chemical properties of water.
a).The formation of water from oxygen and hydrogen.
b).Dissociation of water into ions.
c).Photodissociation of water.
d).Radiolysis of water.
e).Oxidation of water with atomic oxygen.
f).Interaction of water with non metals,halogens,
hydrocarbons.
g).The interaction of water with metals.
h).The interaction of water with oxides.
and).Water as a catalyst and inhibitor of chemical
reactions.
*III* *.
Conclusion.
*  Water as one of the main riches of humanity on Earth.
