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

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

Water is a super-significant substance for our planet. Without it, life on Earth is impossible; not a single geological process takes place without it. The great scientist and thinker Vladimir Ivanovich Vernadsky wrote in his works that there is no such component, the value of which could "compare with it in terms of its influence on the course of the main, most formidable geological processes." Water is present not only in the body of all living beings on our planet, but also in all substances on Earth - in minerals, in rocks ... The study of the unique properties of water constantly reveals more and more secrets to us, sets us new mysteries and throws new challenges.

Anomalous properties of water

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

• In accordance with the laws established by the principle of similarity, within the framework of such sciences as chemistry and physics, we might expect that:
  • water will boil at minus 70°C, and freeze at minus 90°C;
  • water will not drip from the tip of the tap, but will flow in a thin stream;
  • 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 water surface 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 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 get acquainted with the interpretation of the term PURE WATER according to our website, you need to read the article PURE WATER (read →).

water color

Water color - depends on the chemical composition and mechanical impurities

For example, let's take the definition of "Colors of the Sea", given by the "Great Soviet Encyclopedia".

The color of the sea. The color perceived by the eye when the observer looks at the surface of the sea, The color of the sea depends on the color 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. The color of sea water is understood as the color perceived by the eye when viewing sea water vertically over a white background. Only an insignificant part of the light rays incident on it is reflected from the sea surface, the rest of them penetrate deep into, where they are absorbed and scattered by water molecules, particles of suspended matter and the smallest gas bubbles. The scattered rays reflected and emerging from the sea create the C. m. Water molecules scatter the blue and green rays most of all. 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 - yellowish green (for example, Baltic Sea). The theoretical side of the doctrine of the C. m. was developed by V. V. Shuleikin and C. V. Raman.

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

The smell of water

Smell of water – Pure water is usually odorless.

Water transparency

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

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

Ecological encyclopedic Dictionary. - Chisinau I.I. Grandpa. 1989

TRANSPARENCY OF WATER - the ability of water to transmit light rays. It depends on the thickness of the water layer passed by the rays, the presence of suspended impurities, dissolved substances, etc. In water, red and yellow rays are absorbed more strongly, 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

The 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 palpable 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, 0°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, i.e. from liquid to vapor or gas. The boiling point increases as the external pressure increases and decreases as it decreases. It is usually measured at a standard pressure of 1 atmosphere (760 mm Hg). The boiling point of water at a 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, gaseous) can exist simultaneously. For water, the triple point is at a temperature of 273.16 K and a pressure of 610 Pa.

Scientific and technical encyclopedic dictionary.

Surface tension of water

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

Hardness of water

Marine vocabulary

WATER HARDNESS (Stiffness of Water) - a property of water, bled 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. Zh. 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 contributes to the strong formation of scale on their walls, which can cause burnout of the boiler tubes. Boilers of large capacities and especially high pressures 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 apparatuses).

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

Scientific and technical encyclopedic dictionary

HARDNESS OF WATER, 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 water, which enters the water upon contact with limestone. In hot or boiling water, calcium carbonate precipitates in the form of solids. lime deposits on surfaces inside boilers. Calcium carbonate also prevents soap from lathering. The ion-exchange container (3) is filled with granules coated with sodium-containing materials. with which the 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

MINERALIZATION OF WATER - saturation of water inorganic. (mineral) substances present 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 edition of the Moldavian Soviet Encyclopedia. I.I. Grandpa. 1989

Viscosity of water

Viscosity of water 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 appearance of a friction force during movement. It is a factor that transfers motion from layers of water moving at a high speed to layers with a lower speed. V. in. depends on the temperature and concentration of the solution. Physically, it is estimated by the 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. Paffengolts et al. 1978

There are two types of water viscosity:

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

• The kinematic viscosity of water is 0.01012 cm2/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 state (gaseous and liquid phases).

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

Dielectric constant of water

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

In the case of water, this figure is unusually high and for static electric fields 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 peaty 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 1K. It is measured in J / K.kg (where J is JOUL). Substances with a high specific heat capacity, such as water, require more energy to raise the temperature than substances with low specific heat.

Scientific and technical encyclopedic dictionary.

Thermal conductivity of water

The thermal conductivity of a substance refers to its ability to conduct heat from its hotter parts to its colder parts.

Heat transfer in water occurs either at the molecular level, that is, it is 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.

Water fluidity

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 stresses.

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 THE DENSITY OF WATER(read →) .

Water compressibility

The compressibility of water is negligible 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 depends largely on the amount of salts dissolved in them.

Water radioactivity

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

Physical and chemical properties of water

Dictionary of hydrogeology and engineering geology

PHYSICAL AND CHEMICAL PROPERTIES OF WATER - parameters that determine physical and chemical features natural waters. These include indicators of hydrogen ion concentration (pH) and redox 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 redox 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. Manuylov, V. I. Rodionov.

Interaction of water with metals

When water interacts with most metals, a reaction occurs with the release of hydrogen:

• 2Na + 2H2O = H2 + 2NaOH (violently);
• 2K + 2H2O = H2 + 2KOH (violently);
• 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

Of non-metals, for example, carbon and its hydrogen bond(methane). These substances are much less active than metals, but still able to react with water at high temperatures:

• C + H2O = H2 + CO (with strong heating);
• CH4 + 2H2O = 4H2 + CO2 (with strong heating).

Interaction of water with electric current

When exposed electric shock water decomposes into hydrogen and oxygen. It 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 compound reactions:

SO2 + H2O = H2SO3 (sulphurous 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 + 5H2O = CuSO4.5H2O;
• CuSO4 - substance white color(anhydrous copper sulfate);
• CuSO4.5H2O is a crystalline hydrate ( blue vitriol), 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, remove water vapor from moist atmospheric air.

Biosynthesis

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

6n CO 2 + 5n H 2 O \u003d (C 6 H 10 O 5) n + 6n O 2 (under the action of 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 in a complex way, and not in the context of its individual manifestations.

In preparing the material, information was used from 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. Manuylov, V. I. Rodionov and others.

Water is the most unique substance, the basis of all living organisms on the planet. She can acquire different shape and be in three states. What are the main physical and chemical properties of water? It is about them that we will discuss in our article.

Water is...

Water is the most common inorganic compound on our planet. The physical and chemical properties of water are determined by the composition of its molecules.

Thus, the structure of a water molecule contains two hydrogen atoms (H) and one oxygen atom (O). Under normal environmental conditions, it is a tasteless, odorless and colorless liquid. Water can also be in other states: in the form of steam or in the form of ice.

More than 70% of our planet is covered by water. Moreover, about 97% falls on the seas and oceans, so most of it is not suitable for human consumption. What are the main chemical properties drinking water- you will learn further.

Water in nature and human life

Water is an essential component of any living organism. In particular, the human body, as is known, consists of more than 70% of water. Moreover, scientists suggest that it was in this environment that life on Earth originated.

Water is contained (in the form of water vapor or droplets) in different layers of the atmosphere. It comes to the earth's surface from the atmosphere in the form of rain or other precipitation (snow, dew, hail, hoarfrost) through condensation processes.

Water is the object of research for a number of scientific disciplines. Among them are hydrology, hydrography, hydrogeology, limnology, glaciology, oceanology and others. All these sciences, one way or another, study the physical and chemical properties of water.

Water is actively used by man in his economic activities, in particular:

• for growing crops;
• in industry (as a solvent);
• in the energy sector (as a coolant);
• to extinguish fires;
• in cooking;
• in pharmacy and so on.

Of course, in order to effectively use this substance in economic activities, it is necessary to study in detail the chemical properties of water.

Varieties of water

As mentioned above, water in nature can be in three states: liquid (actually, water), solid (ice crystals) and gaseous (steam). It can also take on any form.

There are several types of water. So, depending on the content of Ca and Na cations, water can be:

• hard;
• soft.

• fresh;
• mineral;
• brackish.

In esotericism and some religions there is water:

• dead;
• live;
• saint.

In chemistry, there are also such concepts as distilled and deionized water.

The formula of water and its biological significance

Hydrogen oxide is what chemists call this substance. The formula for water is: H 2 O. It means that this compound consists of one oxygen atom and two hydrogen atoms.

The unique chemical properties of water determined its exceptional role for the life of living organisms. It is thanks to the water biological life exists on our planet.

The most unique feature of water is that it perfectly dissolves a huge amount of other substances (both organic and inorganic origin). An important consequence of this feature is that all chemical reactions in living organisms proceed fairly quickly.

In addition, thanks to unique properties water, it is in a liquid state, with an extremely wide temperature range.

Physical properties of water

Thanks to unique hydrogen bonds, water, under standard environmental conditions, is in a liquid state. This explains the extremely high boiling point of water. If the molecules of the substance were not connected by these hydrogen bonds, then the water would boil at +80 degrees, and freeze - as much as -100 degrees.

Water boils at +100 degrees Celsius, and freezes at zero degrees. Indeed, under certain specific conditions it can begin to freeze even at positive temperatures. When water freezes, it expands in volume (due to a decrease in density). By the way, this is almost the only substance in nature that has a similar physical property. In addition to water, only bismuth, antimony, germanium and gallium expand upon freezing.

The substance is also characterized by high viscosity, as well as a rather strong surface tension. Water is an excellent solvent for polar substances. You should also know that water conducts electricity through itself very well. This feature is explained by the fact that water almost always contains a large number of ions of salts dissolved in it.

Chemical properties of water (grade 8)

Water molecules have extremely high polarity. Therefore, this substance in reality consists not only of simple H 2 O molecules, but also of complex aggregates (formula - (H 2 O) n).

Chemically, water is very active, it reacts with many other substances, even at ordinary temperatures. When interacting with oxides of alkali and alkaline earth metals, it forms bases.

Water is also capable of dissolving a wide range of chemical substances- salts, acids, bases, some gases. For this property, it is often called universal solvent. All substances, depending on whether they dissolve in water or not, are usually divided into two groups:

• hydrophilic (dissolves well in water) - salts, acids, oxygen, carbon dioxide etc.;
• hydrophobic (poorly soluble in water) - fats and oils.

Water also enters into chemical reactions with some metals (for example, sodium), and also takes part in the process of plant photosynthesis.

Finally...

Water is the most abundant inorganic substance on our planet. It is found almost everywhere: on the earth's surface and in its depths, in the mantle and in rocks, in the high layers of the atmosphere, and even in space.

The chemical properties of water are determined by its chemical composition. It belongs to the group of chemical active substances. With many substances, water enters into

Water plays exclusively important role in nature. It creates favorable conditions for the life of plants, animals, microorganisms. Water remains a liquid in the temperature range most favorable for their life processes; for a huge mass of organisms, it is a habitat. The unique properties of water are of unique value for the life of organisms. In reservoirs, water freezes from top to bottom, which is of great importance for the organisms living in them.

The abnormally high specific heat capacity of water favors the accumulation of an enormous amount of heat, contributes to slow heating and cooling. Organisms living in water are protected from sharp spontaneous fluctuations in temperature and composition, as they constantly adapt to slow rhythmic fluctuations - daily, seasonal, annual, and so on. Water has a softening effect on weather and climate conditions. It is constantly moving in all spheres of the Earth, along with the circulation flows of the atmosphere - over long distances. The circulation of water in the ocean (sea currents) leads to planetary heat and moisture exchange. The role of water as a powerful geological factor is known. Exogenous geological processes on Earth are associated with the activity of water as an eroding agent. Erosion and destruction of rocks, soil erosion, transport and deposition of substances are important geological processes associated with water.

Most organic substances in the biosphere are products of photosynthesis, as a result of which organic substances are formed from carbon dioxide and water in plants that use the light energy of the sun. Water is the only source of oxygen released into the atmosphere during photosynthesis. Water is essential for biochemical and physiological processes in the body. Living organisms, including humans, consisting of 80% water, cannot do without it. The loss of 10-20% of water leads to their death.

Water plays a huge role in human life support. It is used by him directly for drinking and household needs, as a means of transportation and raw material for industrial and agricultural products, has a recreational value, its aesthetic significance is great. This is a far from complete enumeration of the role of water in nature and human life.

In nature, water does not occur in a chemically pure form. It is a solution complex composition, which include gases (O 2, CO 2, H 2 S, CH 4 and others), organic and mineral substances. There are suspended particles in moving water streams. The vast majority are found in natural waters. chemical elements. The waters of the oceans contain an average of 35 g/dm 3 (34.6-35.0 ‰) of salts. Their main part is chlorides (88.7%), sulfates (10.8%) and carbonates (0.3%). The least mineralized are the waters of atmospheric precipitation, ultra-fresh waters of mountain streams and fresh lakes.

Depending on the content of dissolved mineral substances, waters are distinguished: fresh with a content of dissolved salts up to 1 g / dm 3, brackish - up to 1-25 g / dm 3, salty - more than 25 g / dm 3. The boundary between fresh and brackish waters is taken according to the average lower limit of human taste perception. The boundary between brackish and saline waters was established on the basis that, with a mineralization of 25 g/dm3, the freezing point and the maximum density quantitatively coincide.

Water is the only substance of nature that under earthly conditions exists in three states of aggregation - solid, liquid, gaseous. The boiling and melting points are taken as reference points on the Celsius temperature scale. This is 0 ° C - the melting point of ice, and 100 ° C - the boiling point of water.

The density of water is -1 g/cm. The density of ice is 0.92 g/cm. Ice, floating on the water, saves water bodies from freezing in winter time. In 1793, the French chemist Antoine Lavoisier proved that water is chemical compound hydrogen with oxygen - hydrogen oxide.

The water molecule has an angular shape: hydrogen atoms with respect to oxygen form an angle equal to 104.5˚. Therefore, the water molecule is a dipole: that part of the molecule where hydrogen is located is positively charged, and the part where oxygen is located is negatively charged. Due to the polarity of water molecules, electrolytes in it dissociate into ions.

In liquid water, along with ordinary H2O molecules, there are associated molecules, i.e., connected in more complex aggregates due to the formation of hydrogen bonds. The presence of hydrogen bonds between water molecules explains the anomalies of its physical properties: the maximum density at 4˚ C, heat boiling, abnormally high heat capacity. As the temperature rises, hydrogen bonds are broken, and their complete rupture occurs when water changes into steam.

The universal structure of water provides it with the ability to move from one state of aggregation to another. This is carried out by melting, evaporation, boiling, condensation, freezing.

Water properties

Physical properties:

Water is a clear liquid with no smell or taste. The mass of 1 ml of pure water is taken as one unit of mass and is called a gram. The low thermal conductivity of water and the high heat capacity explain its use as a heat carrier. Due to its high heat capacity, it cools down for a long time in winter, and slowly heats up in summer, thus being a natural temperature regulator on the globe. Special properties water, distinguishing it from other bodies, are called water anomalies:

• When water is heated from 0°C to 4°C, water decreases in volume, reaching a maximum density of 1g/ml.
• When water freezes, it expands, and does not shrink, like all other bodies, while its density decreases. / 14.15 /
• The freezing point of water decreases with increasing pressure, and does not rise, as one would expect.
• Due to the dipole moment, water has a greater dissolving and dissociating power than other liquids.
• Water has the highest surface tension after mercury. Surface tension and density determine the height to which a liquid can rise in a capillary system when filtered through simple barriers.

The value of water in nature

Water is the most important mineral on Earth, which cannot be replaced by any other substance. It makes up the majority of any organisms, both plant and animal, in particular, in humans, it accounts for 60-80% of body weight. Water is the habitat of many organisms determines the climate and weather changes, helps to cleanse the atmosphere from harmful substances, dissolves, leaches rocks and minerals and transports them from one place to another.

Water saturates the atmosphere with oxygen.

Water is the cause of evolution on Earth. The water cycle is a complex process consisting of several main links: evaporation, water vapor transport by air currents, precipitation, surface and underground runoff, water enters the ocean. It's not only important point origin of life on the planet, but necessary condition sustainable functioning of the biosphere.

Types of water pollution

A body of water or water source is associated with its surroundings. external environment. It is influenced by the conditions for the formation of surface or ground water runoff, various natural phenomena, industry, industrial and public construction, transport, economic and household activities person. The consequence of these influences is the introduction into aquatic environment new, unusual substances - pollutants that degrade water quality. Pollution entering the aquatic environment is classified in different ways, depending on the approaches, criteria and tasks. So usually allocate chemical, physical and biological pollution.

In our country, there are special institutions that systematically control water quality. The Committee of Standards developed norms for the composition of drinking and industrial water.

Hardness of water

Water hardness is a set of chemical and physical properties of water related to the content of dissolved salts of alkaline earth metals in it, mainly calcium and magnesium. The hardness of natural waters can vary within fairly wide limits and is not constant throughout the year. Hardness increases due to evaporation of water, decreases during the rainy season, as well as during the melting of snow and ice.

Water (hydrogen oxide) is a transparent liquid that has no color (in a small volume), smell and taste. Chemical formula: H2O. In the solid state it is called ice or snow, and in the gaseous state it is called water vapor. About 71% of the Earth's surface is covered with water (oceans, seas, lakes, rivers, ice at the poles).

It is a good highly polar solvent. AT natural conditions always contains dissolved substances (salts, gases). Water is of key importance in the creation and maintenance of life on Earth, in the chemical structure of living organisms, in the formation of climate and weather.

Almost 70% 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 falls on the share of salty waters of the World Ocean, and only 35 million cubic kilometers falls on fresh water. The total amount of ocean water would be enough to cover it Earth layer over 2.5 km. For each 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% is in aquifers underground, and only 0.006% of fresh water is simultaneously contained in the channels of all rivers. Water molecules have been found in interstellar space. Water is part of comets, most planets solar system and their companions.

The composition of water (by mass): 11.19% hydrogen and 88.81% oxygen. Pure water is clear, odorless and tasteless. It has the highest density at 0°C (1 g/cm3). The density of ice is less than the density of liquid water, so ice floats to the surface. Water freezes at 0°C and boils at 100°C at a pressure of 101,325 Pa. It is a poor conductor of heat and a very poor conductor of electricity. Water is a good solvent. The water molecule has an angular shape; hydrogen atoms form an angle of 104.5° with respect to oxygen. Therefore, the water molecule is a dipole: that part of the molecule where hydrogen is located is positively charged, and the part where oxygen is located is negatively charged. Due to the polarity of water molecules, electrolytes in it dissociate into ions.

In liquid water, along with ordinary H20 molecules, there are associated molecules, i.e., combined into more complex aggregates (H2O)x due to the formation of hydrogen bonds. The presence of hydrogen bonds between water molecules explains the anomalies of its physical properties: maximum density at 4 ° C, high boiling point (in the series H20-H2S - H2Se) anomalously high heat capacity. As the temperature rises, hydrogen bonds break, and a complete break occurs when water changes into steam.

Water is a highly reactive substance. At normal conditions it interacts with many major and acid oxides, as well as with alkali and alkaline earth metals. Water forms numerous compounds - crystalline hydrates.

Obviously, water-binding compounds can serve as desiccants. Other drying agents include P205, CaO, BaO, metallic Ma (they also chemically interact with water), and silica gel. To important chemical properties water is its ability to enter into reactions of hydrolytic decomposition.

Physical properties of water.

Water has a number of unusual features:

1. When ice melts, its density increases (from 0.9 to 1 g/cm³). For almost all other substances, the density decreases when melted.

2. When heated from 0 °C to 4 °C (more precisely, 3.98 °C), water contracts. Accordingly, as it cools, the density decreases. Thanks to this, fish can live in freezing waters: when the temperature drops below 4 ° C, more cold water as the less dense one remains on the surface and freezes, while a positive temperature remains under the ice.

3. High temperature and specific heat of fusion (0 °C and 333.55 kJ/kg), boiling point (100 °C) and specific heat of vaporization (2250 kJ/kg), compared to hydrogen compounds with similar molecular weight.

4. High heat capacity of liquid water.

5. High viscosity.

6. High surface tension.

7. Negative electric potential water surface.

All these features are associated with the presence of hydrogen bonds. Due to the large difference in the electronegativity of hydrogen and oxygen atoms, electron clouds are strongly shifted towards oxygen. Because of this, as well as the fact that the hydrogen ion (proton) does not have internal electron layers and has small dimensions, it can penetrate into the electron shell of a negatively polarized atom of a neighboring molecule. Due to this, each oxygen atom is attracted to the hydrogen atoms of other molecules and vice versa. A certain role is played by the proton exchange interaction between and within water molecules. Each water molecule can participate in a maximum of four hydrogen bonds: 2 hydrogen atoms - each in one, and an oxygen atom - in two; in this state, the molecules are in an ice crystal. When ice melts, some of the bonds break, which allows the water molecules to be packed more densely; when water is heated, the bonds continue to break, and its density increases, but at temperatures above 4 ° C, this effect becomes weaker than thermal expansion. Evaporation breaks all remaining bonds. Breaking bonds requires a lot of energy, hence the high temperature and specific heat of melting and boiling and high heat capacity. The viscosity of water is due to the fact that hydrogen bonds prevent water molecules from moving at different speeds.

For similar reasons, water is a good solvent for polar substances. Each solute molecule is surrounded by water molecules, and the positively charged parts of the solute molecule attract oxygen atoms, and the negatively charged parts attract hydrogen atoms. Because the water molecule is small, many water molecules can surround each solute molecule.

This property of water is used by living beings. In a living cell and in the intercellular space, solutions of various substances in water interact. Water is necessary for the life of all unicellular and multicellular living beings on Earth without exception.

Pure (free of impurities) water is a good insulator. Under normal conditions, water is weakly dissociated and the concentration of protons (more precisely, hydronium ions H3O+) and hydroxide ions HO− is 0.1 µmol/L. But since water is a good solvent, certain salts are almost always dissolved in it, that is, there are positive and negative ions. As a result, water conducts electricity. The electrical conductivity of water can be used to determine its purity.

Water has a refractive index n=1.33 in the optical range. However, it strongly absorbs infrared radiation, and therefore water vapor is the main natural greenhouse gas responsible for more than 60% of the greenhouse effect. Due to the large dipole moment of the molecules, water also absorbs microwave radiation, on which the principle of the microwave oven is based.

aggregate states.

1. According to the state, they distinguish:

2. Solid - ice

3. Liquid - water

4. Gaseous - water vapor

Fig.1 "Types of snowflakes"

At atmospheric pressure Water freezes (turns into ice) at 0°C and boils (turns into water vapor) at 100°C. As the pressure decreases, the melting point of water slowly rises and the boiling point falls. At a pressure of 611.73 Pa (about 0.006 atm), the boiling and melting points coincide and become equal to 0.01 ° C. This pressure and temperature is called the triple point of water. At lower pressures, water cannot be in a liquid state, and ice turns directly into steam. The sublimation temperature of ice decreases with decreasing pressure.

With an increase in pressure, the boiling point of water increases, the density of water vapor at the boiling point also increases, and liquid water decreases. At a temperature of 374 °C (647 K) and a pressure of 22.064 MPa (218 atm), water passes the critical point. At this point, the density and other properties of liquid and gaseous water are the same. With more high pressure there is no difference between liquid water and water vapor, hence no boiling or evaporation.

Metastable states are also possible - supersaturated vapor, superheated liquid, supercooled liquid. These states can exist for a long time, but they are unstable and a transition occurs upon contact with a more stable phase. For example, it is not difficult to obtain a supercooled liquid by cooling clean water in a clean vessel below 0 °C, however, when a crystallization center appears, liquid water quickly turns into ice.

Isotopic modifications of water.

Both oxygen and hydrogen have natural and artificial isotopes. Depending on the type of isotopes included in the molecule, the following types of water are distinguished:

1. Light water (just water).

2. Heavy water (deuterium).

3. Superheavy water (tritium).

Chemical properties of water.

Water is the most common solvent on Earth, largely determining the nature of terrestrial chemistry as a science. Most of chemistry, at its inception as a science, began precisely as chemistry aqueous solutions substances. It is sometimes considered as an ampholyte - both an acid and a base at the same time (cation H + anion OH-). In the absence of foreign substances in water, the concentration of hydroxide ions and hydrogen ions (or hydronium ions) is the same, pKa ≈ approx. 16.