MOU Maninskaya secondary school

Open lesson in geography

V class

Teacher:

2008 year.

Lesson topic: “Water is a solvent. The work of water in nature ”.

Lesson objectives:

Introduce students to the meaning of water on Earth.

Give the concept of solutions and suspensions, soluble and water-insoluble substances

Show the work of water in nature (creative and destructive)

To foster respect for water, love for beauty.

Equipment: hemisphere map, globe, a statement about water, tables "Sea surf", "Cave", "Ocean", "Inhabitants of the seas and oceans", "Weathering", test tubes with water, salt, sand, filter, tape recorder, TV, multimedia projector ...

During the classes.

I.Organizing time.

II.Learning new material.

The lesson begins with watching a fragment of a film about water.

Against the background of soft music, reflecting the sounds of water.

Teacher:

The vastness of the ocean

And the quiet backwater of the pond,

And it's all just water

The topic of our lesson is “Water is a solvent. The work of water in nature ”.

The academician spoke brightly and accurately about the role of water in nature. “Is water just a liquid that has been poured into a glass?

The ocean that covers almost the entire planet, our entire wonderful Earth, in which life was born millions of years ago, is water. "

Clouds, clouds, fog, carrying moisture to all living things on the earth's surface - this is also water.

They seem to be dressed in lace

Trees, bushes, wires,

And it seems like a fairy tale

And, in essence, only water.

The variety of life is limitless. She is everywhere on our planet. But life is only where there is water. There is no living entity if there is no water. Yes, today in our lesson we will talk about water, about the Queen - Voditsa. Let's do a little warm-up.

Guess riddles.

1. Walks under the ground,

Looks at the sky. ( spring)

2. What is visible when nothing is visible. ( fog)

3. In the evening flies to the ground,

Night remains on earth

Flies away again in the morning. ( dew)

4. They fly without wings,

They run without legs

They sail without a sail. ( clouds)

5. Not a horse, but runs,

Not a forest, but a noise. ( river, stream).

6. Came - knocked on the roof,

He left - no one heard. ( rain)

Let's take a look at the globe. Our planet was named Earth due to an obvious misunderstanding: ¼ of its territory falls on land, and everything else is water. It would be correct to call it the planet Water! There is a lot of water on earth, but there is no absolutely pure water in nature, it is always present, some impurities, some of them are desirable, since the human body needs it. Others can be hazardous to health and render the water unusable.

1. Water is a solvent.

There are no substances that, at least to a small extent, do not dissolve in water. Even gold, silver, iron, glass dissolve in water to an insignificant degree. Scientists have calculated that, for example, when we drink a glass of hot tea, we absorb about 0.0001 g of dissolved glass with it. Due to the ability of water to dissolve other substances, it can never be called absolutely pure.

Demonstration of experience: water as a solvent.

Pour salt into a glass of water and stir it with a spoon. What happens to salt crystals? They get smaller and smaller and soon disappear altogether. But has the salt disappeared?

No. She dissolved in water. We got a salt solution.

Let's pass the salt solution through the filter. Nothing has settled on the filter. The salt solution passed freely through the filter. What is called a solution?

Solution - liquid containing foreign substances that are evenly distributed in it .

Demonstration of experience: experience with clay.

Let's do the same experiment with clay. Clay particles float in water. Let's pass the water through the filter. The water passed through it, and the clay particles remained on the filter.

From this experience, it can be concluded that clay does not dissolve in water.

What is the difference between the results of the two experiments? ( water with dissolved salt is clear, but water with clay is not)

Indeed, natural water can contain various particles that do not dissolve in it. These particles make it cloudy. In this case, they talk about suspensions... After standing for some time, the cloudy liquid becomes transparent. Insoluble particles of the substance sink to the bottom. And in solutions, no matter how much they stand, substances do not settle to the bottom.

People have long noticed that water poured into silver vessels does not deteriorate for a long time. The fact is that it contains dissolved silver, which has a detrimental effect on bacteria in the water. "Silver" water is used by astronauts during their flights.

How can you make silver water at home?

Not only solid and liquid substances dissolve in water, but also gases: oxygen, nitrogen, carbon dioxide.

Fish, plants and animals breathe oxygen dissolved in water.

Getting carbonated water is based on the dissolution of carbon dioxide in water.

Physical education "Water is not water"

A game of mindfulness. I name words. If the named word means that which contains water (cloud), then the children should stand up. If an object or phenomenon is indirectly related to water (ship), children raise their hand. If an object or phenomenon is called that has no connection with water (wind), children clap their hands.

Puddle, boat, rain, sand, waterfall, stone, diver, snow, tree, beach, seal, car, cloud.

2. The work of water in nature.

Many phenomena on the Earth's surface involve water.

So, streams of melt water, uniting, become formidable streams, and can bring great destruction. This is how ravines are formed ( demonstration of "bas-relief", "formation of a ravine").

The water washes away the top layer of fertile soil.

Under the influence of water, rocks are slowly destroyed ( story according to the "Weathering" table). There is a proverb among the people "Water wears away a stone."

As it seeps into the ground, water erodes and dissolves various rocks. This is how voids are formed underground - caves ( table "Caves").

The terrible natural disasters such as floods and tsunamis are well known.

During floods and tsunamis, water destroys bridges, destroys banks and buildings, destroys crops of cultivated plants, and takes human lives.

Student message "Floods".

Flooding is the inundation of an area, settlements, industrial and agricultural facilities, causing damage. Floods lead to the destruction of economic facilities, the death of crops, forests and the forced evacuation of the population from the flooded zone. Floods, which lead not only to destruction, but also to human casualties, are called disastrous.

They can be caused by heavy downpours, amicable melting of snows after a snowy winter.

Student's message "Tsunami"

Tsunami is a rare but very formidable natural phenomenon. The word "tsunami" in Japanese means "a big wave that floods the bay." These waves can be insignificant and even imperceptible, but they can also be catastrophic. Devastating tsunamis are caused mainly by strong underwater earthquakes at great depths of the seas and oceans, as well as underwater volcanic eruptions. At the same time, billions of tons of water are set in motion in short periods of time. Low waves appear, traveling along the surface of the ocean at the speed of a jet plane - 700-800 kilometers per hour.

In the open ocean, even the most formidable tsunamis are not dangerous at all. Tragedies are played out when tsunami waves approach the coastal shallow water area. On the shore, waves reach 10-15 meters and more.

The consequences of tsunamis can be catastrophic: they cause enormous destruction, claiming hundreds of thousands of human lives.

The largest number of tsunamis originate on the Pacific coast (about once a year).

Teacher: what work does water do in all these examples?

(destructive)

But water does more than just destructive work. During spring floods, river water brings fertile silt to some areas of the land. Vegetation develops very well on them.

Not a single process in living organisms takes place without the participation of water. Plants need it to absorb substances from the soil, move them along the stem, leaves, in the form of solutions, for seed germination.

All living and nonliving: any soil, rocks, all objects, bodies, organisms - consist of water.

For example, in the human body, water accounts for 60 - 80% of the total mass.

Water plays an important role in the life of human society. Man turned reservoirs into transport routes, river flows - a source of cheap electricity.

Water is the habitat of many living organisms that cannot be found on land (f Ragment of the video of the film "Inhabitants of the seas and oceans")

Water resources are the national wealth of our country, which requires careful treatment: strict accounting, protection from pollution, economical use.

Teacher: A do we always use water sparingly?

Remember the person forever:

The symbol of life on earth is water!

Save it and take care -

We are not alone on the planet!

III... Anchoring

1. Questions:

a) What are the names of all seas and oceans taken together ( world Ocean)

b) Not the sea, not the land - ships don't float and you can't walk ( swamp)

b) All around water and drinking - trouble ( sea)

d) Guess what substance we are talking about: This substance is very common in nature, but practically does not occur in its pure form. Life is impossible without this substance. Among the ancient peoples, it was considered a symbol of immortality and fertility. In general, it is the most extraordinary liquid in the world. What is it? ( water).

2. The game "Cross out the unnecessary" (cards with the task on the students' tables)

Assignment: delete an extra word and explain why?

a) Snow, ice, steam, hail.

b) Rain, snowflake, sea, river.

c) Hail, water vapor, snow, rain.

3. And now the next task. Fill in the gaps in the text:

Water ... solvent. Solids dissolve in it.

For example ...: liquid substances, for example ... gaseous substances,

for example…

In this regard, it is impossible to find in nature ... water.

4. Game "Superfluous property"

Assignment: Cross out the property that does not apply to water.

Property:

a) Has color, has no color.

b) Taste, tasteless.

c) Has a smell, no smell.

d) Opaque, transparent.

e) Possesses fluidity, does not possess fluidity.

f) Heats up quickly and cools down quickly, heats up slowly and cools down slowly.

g) Dissolves sand and chalk, dissolves salt and sugar.

h) Has a shape, has no shape.

Against the background of music

Teacher:

Water is a wonderful natural gift,

Alive, fluid and free

He paints the pictures of our life.

In its three important guises.

Now it winds like a stream, then like a river,

That pours from the glass to the ground.

It freezes into a thin piece of ice,

A beautifully named snowflake.

It takes on the lightness of steam:

Was - and suddenly she was gone.

Great worker voditsa,

Well, how could she not admire her.

She floats towards us in clouds

Feeds with snow and rain

And destroys and inflicts

And so he asks for our care.

IV... Homework§ 23, task 77 workbook. p. 45

The energy of formation of water molecules is high, it is 242 kJ / mol. This explains the stability of water in natural conditions. Stability, combined with electrical characteristics and molecular structure, make water an almost universal solvent for many substances. The high dielectric constant determines the highest dissolving power of water in relation to substances whose molecules are polar. Of inorganic substances, very many salts, acids and bases are soluble in water. Of organic substances, only those soluble are those in the molecules of which polar groups constitute a significant part - many alcohols, amines, organic acids, sugars, etc.

Dissolution of substances in water is accompanied by the formation of weak bonds between their molecules or ions and water molecules. This phenomenon is called hydration. For substances with an ionic structure, the formation of hydration shells around the cations is characteristic due to the donor-acceptor bond with the lone pair of electrons of the oxygen atom. The smaller their radius and the higher the charge, the more hydrated the cations are. Anions, usually less hydrated than cations, attach hydrogen molecules to water molecules.

In the process of dissolution of substances, the magnitude of the electric moment of the dipole of water molecules changes, their spatial orientation changes, some hydrogen bonds are broken and other hydrogen bonds are formed. Together, these phenomena lead to a restructuring of the internal structure.

The solubility of solids in water depends on the nature of these substances and temperature and varies widely. An increase in temperature in most cases increases the solubility of the salts. However, the solubility of such compounds as CaSO 4 2H 2 O, Ca (OH) 2 decreases with increasing temperature.

With mutual dissolution of liquids, one of which is water, various cases are possible. For example, alcohol and water mix with each other in any ratio, since both are polar. Gasoline (non-polar liquid) is practically insoluble in water. The most common is the case of limited mutual solubility. An example is the water – ether and water – phenol systems. When heated, the mutual solubility for some liquids increases, for others it decreases. For example, for the water – phenol system, an increase in temperature above 68 ° С leads to unlimited mutual solubility.

Gases (for example, NH 3, CO 2, SO 2) are readily soluble in water, as a rule, when they enter into chemical interaction with water; usually the solubility of gases is low. As the temperature rises, the solubility of gases in water decreases.

It should be noted that the solubility of oxygen in water is almost 2 times higher than the solubility of nitrogen. As a result, the composition of the air dissolved in the water of reservoirs or treatment facilities differs from the atmospheric one. Dissolved air is enriched with oxygen, which is very important for organisms that live in the aquatic environment.

For aqueous solutions, as well as for any others, a decrease in the freezing point and an increase in the boiling point are characteristic. One of the general properties of solutions is manifested in the phenomenon of osmosis. If two solutions of different concentrations are separated by a semi-permeable partition, solvent molecules penetrate through it from a dilute solution to a concentrated one. The mechanism of osmosis can be understood if we take into account that, according to the general natural principle, all molecular systems tend to the state of the most uniform distribution (in the case of two solutions - the desire to equalize the concentrations on both sides of the partition).

The most common solvent on our planet is water. The body of an average person weighing 70 kg contains about 40 kg of water. In this case, about 25 kg of water is the liquid inside the cells, and 15 kg is the extracellular fluid, which includes blood plasma, intercellular fluid, cerebrospinal fluid, intraocular fluid and liquid contents of the gastrointestinal tract. In animals and plants, water is usually more than 50%, and in some cases the water content reaches 90-95%.

Due to its anomalous properties, water is a unique solvent, perfectly adapted for life.

First of all, water dissolves well ionic and many polar compounds. This property of water is connected, to a large extent, with its high dielectric constant (78.5).

Another numerous class of substances that are well soluble in water includes such polar organic compounds as sugars, aldehydes, ketones, alcohols. Their solubility in water is explained by the tendency of water molecules to form polar bonds with polar functional groups of these substances, for example, with hydroxyl groups of alcohols and sugars or with the oxygen atom of the carbonyl group of aldehydes and ketones. Below are examples of hydrogen bonds that are important for the solubility of substances in biological systems. Due to the high polarity of water, it causes hydrolysis of substances.

Since water is the main part of the internal environment of the body, it provides the processes of absorption, movement of nutrients and metabolic products in the body.

It should be noted that water is the end product of biological oxidation of substances, in particular glucose. The formation of water as a result of these processes is accompanied by the release of a large amount of energy - approximately 29 kJ / mol.

Other anomalous properties of water are also important: high surface tension, low viscosity, high melting and boiling points, and higher density in the liquid state than in the solid state.

Water is characterized by the presence of associates - groups of molecules connected by hydrogen bonds.

Depending on the affinity for water, the functional groups of soluble particles are subdivided into hydrophilic (attracting water), easily solvated by water, hydrophobic (repelling water) and diphilic.

The hydrophilic groups include polar functional groups: hydroxyl -OH, amino -NH 2, thiol -SH, carboxyl -COOH. To hydrophobic - non-polar groups, such as hydrocarbon radicals: CH3- (CH 2) p -, C 6 H 5 -. Substances (amino acids, proteins), the molecules of which contain both hydrophilic groups (-OH, -NH 2, -SH, -COOH) and hydrophobic groups: (CH 3 - (CH 2) p, - C 6 H 5 -).

When amphiphilic substances dissolve, the structure of water changes as a result of interaction with hydrophobic groups. The degree of ordering of water molecules close to the hydrophobic groups increases, and the contact of water molecules with hydrophobic groups is reduced to a minimum. When hydrophobic groups associate, they push water molecules out of their area.

Water purification methods- ways of separating water from unwanted impurities and elements. There are several cleaning methods and they all fall into three groups of methods:

Mechanical

Physicochemical

Biological

The cheapest - mechanical cleaning - is used for the release of suspended matter. The main methods are straining, settling and filtering. They are applied as preliminary steps.

Chemical treatment is used to separate soluble inorganic impurities from wastewater. When wastewater is treated with reagents, it is neutralized, dissolved compounds are released, and the effluent is discolored and disinfected.

Physicochemical treatment is used to treat wastewater from coarse and finely dispersed particles, colloidal impurities, and dissolved compounds. A high-performance, but at the same time expensive method of cleaning.

Biological methods are used to remove dissolved organic compounds. The method is based on the ability of microorganisms to decompose dissolved organic compounds.

At present, out of the total amount of wastewater, 68% of all wastewater is subjected to mechanical treatment, physical and chemical - 3%, biological - 29%. In the future, it is planned to increase the share of biological treatment to 80%, which will improve the quality of the treated water.

The main method of improving the quality of treatment of harmful emissions by enterprises in a market economy is a system of fines, as well as a system of fees for the use of treatment facilities.

Halogens(from the Greek ἁλός - salt and γένος - birth, origin; sometimes the outdated name is used halides) - chemical elements of the 17th group of the periodic table of chemical elements of D.I.Mendeleev (according to the outdated classification - the elements of the main subgroup of the VII group).

Reacts with almost all simple substances, except for some non-metals. All halogens are energetic oxidizing agents, therefore they are found in nature only in the form of compounds. With an increase in the serial number, the chemical activity of halogens decreases, the chemical activity of halide ions F -, Cl -, Br -, I -, At - decreases.

Halogens include fluorine F, chlorine Cl, bromine Br, iodine I, astatine At, and also (formally) the artificial element ununseptium Uus.

All halogens are non-metals. On the external energy level, 7 electrons are strong oxidants. When interacting with metals, an ionic bond arises, and salts are formed. Halogens (except for F), when interacting with more electronegative elements, can also exhibit reducing properties up to the highest oxidation state of +7.

Features of fluorine chemistry

the most electronegative element in the periodic table, everything burns in the fluorine atmosphere, even oxygen!

WITH Free fluorine is a greenish-yellow gas with a characteristic pungent and unpleasant odor. Its density in air is 1.13, its boiling point is –187 ° С, and its melting point is –219 ° С. The relative atomic mass of fluorine is 19. In all its compounds, fluorine is monovalent. Fluorine atoms combine to form diatomic molecules.

Fluorine forms compounds, directly or indirectly, with all other elements, including some inert gases.

Fluorine combines with hydrogen even at –252 ° С. At this temperature, hydrogen turns into a liquid and fluorine solidifies, and yet the reaction proceeds with such a strong release of heat that an explosion occurs. For a long time, the compound of fluorine with oxygen was not known, but in 1927 French chemists managed to obtain oxygen difluoride, which is formed by the action of fluorine on a weak alkali solution:

2F 2 + 2NаОН = 2NаF + OF 2 + H 2 O.

Fluorine does not directly combine with nitrogen, but the well-known specialist in fluorine Otto Ruff managed to obtain nitrogen trifluoride NF 3 in 1928 indirectly. Other nitrogen-containing fluorine compounds are also known. Sulfur under its action ignites when exposed to air. Charcoal ignites in a fluorine atmosphere at ambient temperatures.

The simplest means of extinguishing fires - water - burns in a stream of fluorine with a light violet flame.

All metals interact with fluorine under certain conditions. Alkali metals ignite in its atmosphere already at room temperature. Silver and gold in the cold interact with fluorine very slowly, and when heated, they burn out in it. Platinum does not react with fluorine under normal conditions, but it burns out when heated to 500–600 ° C.

From compounds of other halogens with metals, fluorine displaces free halogens, taking their place. Oxygen is also easily displaced by fluorine from most oxygen compounds. So, for example, fluorine decomposes water with the release of oxygen (with an admixture of ozone):

H 2 O + F 2 = 2HF + O.

Combining with hydrogen, fluorine forms a gaseous compound - hydrogen fluoride HF. Aqueous solutions of hydrogen fluoride are called hydrofluoric acid. Gaseous HF is a colorless gas with a pungent odor, which is very harmful to the respiratory organs and mucous membranes. The usual method for its production is the action of sulfuric acid on fluorspar CaF 2:

CaF 2 + H 2 SO 4 = CaSO 4 + 2HF.

Hydrogen fluoride molecules are characterized by the ability of their association (connection). At a temperature of about 90 ° C, a simple HF molecule with a relative molecular weight of 20 is obtained, but when the temperature is lowered to 32 ° C, measurements lead to a double formula H 2 F 2. At a boiling point of hydrogen fluoride equal to 19.4 ° C, associates H 3 F 3 and H 4 F 4 appear. At lower temperatures, the composition of the hydrogen fluoride associates is even more complex.

Hydrofluoric acid acts on all metals except gold and platinum. Hydrofluoric acid acts very slowly on copper and silver. Its weak solutions have absolutely no effect on tin, copper and bronze.

Resistant to hydrofluoric acid and lead, which is covered with a layer of lead fluoride, which protects the metal from further destruction. Therefore, lead also serves as a material for equipment in the production of hydrofluoric acid.

The tendency of HF molecules to association leads to the fact that, in addition to the average salts of hydrofluoric acid, acidic ones are also known, for example, KHF 2 (fluorine is obtained from it by electrolysis). This is its difference from other hydrohalic acids, which give only average salts.

A characteristic feature of hydrofluoric acid, which distinguishes it from all other acids, is its extremely light effect on silica SiO 2 and silicic acid salts:

SiO 2 + 4HF = SiF 4 + 2H 2 O.

Silicon tetrafluoride SiF 4 is a gas that escapes during the reaction.

Acting on the silica that is part of the glass, hydrofluoric acid corrodes the glass; therefore, it cannot be stored in glass vessels.

Of organic substances, hydrofluoric acid acts on paper, wood, cork, charring them. It acts weakly on plastic, does not act at all on paraffin, which is used when storing hydrofluoric acid in vessels made of this material.

F the torus is quite common in nature. Its percentage in the earth's crust is close to the content of elements such as nitrogen, sulfur, chromium, manganese and phosphorus. However, only two fluoride minerals are of industrial importance - fluorspar and cryolite. In addition, fluorine is included in a relatively small amount in the composition of apatites. When natural phosphates are processed into artificial fertilizers, fluoride compounds are obtained as by-products.

Fluorspar, otherwise called fluorite, or fluorite, is in its composition calcium fluoride CaF 2. In nature, fluorspar can occur both in the form of individual crystals and in continuous masses. Geologists explain the formation of deposits of fluorspar as follows. When the once liquid mass of the earth's crust cooled, cracks and voids formed inside it. When solutions or volcanic gases containing fluorine penetrated into such voids that arose inside rocks containing calcium, an interaction occurred between the calcium of the rock and the fluorine of the solution or gas. As a result of this interaction, the voids were filled with a mass of calcium fluoride. This is the origin of fluorspar.

The variety of colors of fluorspar is remarkable: it can be completely colorless (transparent), white, pink, blue, green, red, purple. The most common colors are green and purple.

Powerful deposits of fluorspar are found in the American states of Illinois, Kentucky, Colorado.

Elementary fluorine has so far found its only widespread use: in the disinfection of drinking water. But unlike its analogue chlorine, which serves the same purpose directly, fluorine is used here indirectly. The action of fluorine on water produces ozone, which is used to sterilize drinking water.

By the way, fluoride enters our body with drinking water. With a lack of fluoride, the resistance of tooth enamel against acids contained in food decreases.

Many fluorinated substances are very important for modern science and technology. Of great importance are the compounds of fluorine with carbon, called fluorocarbons. They do not occur in nature and are obtained exclusively artificially. Fluorocarbons have a number of valuable properties: they do not burn, do not corrode, rot, etc. The possibilities of their practical application are constantly expanding. For example, fluorochlorine derivatives of the simplest hydrocarbons (CH 4, etc.) - the so-called freons - They are widely used as refrigerants in refrigeration units on ships, railway cars, domestic refrigerators, etc.

Molecular chlorine and its main compounds

Water is the most abundant substance on Earth, it covers about four-fifths of the earth's surface. It is the only chemical compound that naturally exists in the form of liquid, solid (ice) and gas (water vapor). Water plays a vital role in industry, everyday life and in laboratory practice; it is absolutely essential to sustain life. About two-thirds of the human body is water, and many foods are predominantly water.

Structure and physical properties of water. V 1860s Italian chemist Stanislav Cannizzaro, investigating organic compounds containing -OH groups, named by him hydroxyl, finally established that water has the formula H 2 0.

Water is a covalent molecular compound. Communication O-N covalent polar; angle - 104.5 °. Oxygen, as a more electronegative atom (electronegativity is the ability to attract the total electron density to itself during the formation of a bond) pulls off the electron density common with the hydrogen atom to itself and therefore carries a partial negative charge; hydrogen atoms from which the electron density is displaced carry a partial positive charge. Thus, the water molecule is dipole, those. has positively and negatively charged areas. Water is a clear, colorless liquid with a number of anomalous physical properties. For example, it has abnormally high freezing and boiling points and surface tension. A rare feature of water is that its density in the liquid state at 4 ° C is greater than that of ice. Therefore, ice floats on the surface of the water. These anomalous properties of water are explained by the existence of hydrogen bonds in it, which bind molecules together in both liquid and solid states. Water does not conduct electric current well, but becomes a good conductor if even small amounts of ionic substances are dissolved in it.

Chemical properties of water

1... Acid-base reactions. Water possesses amphoteric properties. This means that it can act both as an acid and as a base. Its amphoteric properties are due to the ability of water to self-ionize:

This allows water to be, on the one hand, a proton acceptor: and on the other hand, a proton donor:

2. Redox reactions. Water has the ability to act as oxidizing agent, and in the role reductant. It oxidizes metals located in the electrochemical series of voltages above tin. For example, in the reaction between sodium and water

the following oxidative process occurs:

In this reaction, water plays the role of a reducing agent:

Another example of a similar reaction is the interaction between magnesium and water vapor:

Water acts as an oxidizing agent in corrosion processes. For example, one of the processes occurring during iron rusting is as follows:

Water is an important reducing agent in biochemical processes. For example, some of the steps in the citric acid cycle involve water recovery:

This electron transfer process is also of great importance in the reduction of organic phosphate compounds during photosynthesis. The citric acid cycle and photosynthesis are complex processes involving a series of sequential chemical reactions. In both cases, the processes of electron transfer occurring in them are not yet fully understood.

• 3.Hydration. Water molecules are capable of solvating both cations and anions. This process is called hydration. Hydrate water in salt crystals is called water of crystallization. Water molecules are usually associated with the cation they solvate by coordination bonds. Indicate the content of hydrated water in the formula of the substance: CuS0 4 4H 2 0.
• 4. Hydrolysis. Hydrolysis is the reaction of an ion or molecule with water. An example of this type of reaction is the reaction between hydrogen chloride and water to form hydrochloric acid. Another example is the hydrolysis of iron (III) chloride:

5. Interaction with active metal oxides: CaO + H 2 0 =

6. Interaction with nonmetal oxides:Р 2 0 5 + Н 2 0 = 2НР0 3.

Water is widely used as a solvent in chemical

technology, as well as in laboratory practice. It is a universal solvent required for biochemical reactions. The fact is that water perfectly dissolves ionic compounds, as well as many covalent compounds. The ability of water to dissolve many substances well is due to the polarity of its molecules, which, when ionic substances are dissolved in water, are oriented around the ions, i.e. solvate them. Aqueous solutions of ionic substances are electrolytes. The solubility of covalent compounds in water depends on their ability to form hydrogen bonds with water molecules. Simple covalent compounds such as sulfur dioxide, ammonia and hydrogen chloride dissolve in water. Oxygen, nitrogen and carbon dioxide are poorly soluble in water. Many organic compounds containing atoms of electronegative elements, such as oxygen or nitrogen, are soluble in water. As an example, let us indicate ethanol C 2 H 5 OH, acetic acid CH3COOH, sugar Ci 2 H 22 0 6. The presence of non-volatile solutes in water, such as sodium chloride or sugar, lowers the vapor pressure and freezing point of water, but increases its boiling point. The presence of soluble calcium and magnesium salts in water (water hardness) makes it difficult to use it in technological processes.

Rigidity water is subdivided into temporary (carbonate, due to the presence of calcium bicarbonates Ca (HC0 3) 2

and magnesium Mg (HCO3) 2) and permanent (non-carbonate) rigidity. According to GOST R 52029-2003, the hardness is expressed in degrees of hardness (° F), which corresponds to the concentration of the alkaline earth element, numerically equal to "/ 2 of its mole, expressed in mg / dm 3 (g / m 3). The total hardness is distinguished by water soft(up to 2 mg-eq / l), medium hardness(2-10 mEq / l) and tough(more than 10 mEq / l).

The water hardness of surface sources fluctuates significantly throughout the year; it is maximum at the end of winter, minimum - during floods (for example, the hardness of the Volga water in March is 4.3 meq / l, in May - 0.5 meq / l). In groundwater, hardness is usually higher (up to 80-100 meq / l) and changes less during the year.

Solubility of gases in water depends on the temperature and the partial pressure of the gas above the water: the lower the temperature and the higher the partial pressure of the gas above the water, the higher the concentration of gas in the liquid.

Solubility of most solids rises with increasing temperature. When a solid dissolves, two processes occur:

• 1) the process of destruction of the crystal lattice. This process requires energy consumption, therefore it is endothermic "
• 2) the process of formation of hydrates (solvates) proceeds with the release of energy.

The total heat of dissolution is the sum of the heats of these two processes, so dissolution can take place both with increasing and decreasing temperature.

Solution is called a homogeneous (homogeneous) system consisting of two or more components. The necessary components of the solution are a solvent and a solute such as sugar dissolved in water. One solvent can contain several solutes. For example, when preparing a marinade, sugar, salt and acetic acid are dissolved in water. Dissolved substances with the same aggregate state of components, components that are in shortage are usually considered, while a component in excess is considered solvent. At different states of aggregation of the components of a solution, a component is usually considered a solvent, the state of aggregation of which coincides with the state of aggregation of the solution. For example, in the case of liquid solutions of solid and gaseous substances, the solvent is always considered to be the liquid component, regardless of the concentration of the dissolved substances. If two liquids are used in the preparation of the solution, the solvent is the one in excess. If water is used in the preparation of the solution, the solvent is water.

In relation to water, practically all substances can be divided into two groups:

1. Hydrophilic(from the Greek "phileo" - to love, having a positive affinity for water ). These substances have a polar molecule containing electronegative atoms (oxygen, nitrogen, phosphorus, etc.). As a result, individual atoms of such molecules also acquire partial charges and form hydrogen bonds with water molecules. Examples: sugars, amino acids, organic acids.
2. Hydrophobic(from the Greek "phobos" - fear, having a negative affinity for water ). The molecules of such substances are non-polar and do not mix with a polar solvent such as water, but they are readily soluble in organic solvents, for example, in ether, and in fats. An example is linear and cyclic hydrocarbons... incl. benzene.

In addition, the transport function of internal fluids in both multicellular animals (blood, lymph, hemolymph, coelomic fluid) and multicellular plants is directly related to the property of water as a solvent.

5. Water as a reagent.
The importance of water is also associated with its chemical properties - as an ordinary substance that enters into chemical reactions with other substances. The most important are the splitting of water under the action of light ( photolysis) in the light phase photosynthesis, the participation of water as a necessary reagent in the decomposition reactions of complex biopolymers (such reactions are not accidentally called hydrolysis reactions ). And, conversely, during the reactions of biopolymer formation, polymerization, water is released.
Question 4. What inaccuracy in the last phrase would a chemist correct?