Because water is a good solvent. main solvent. II. Message about the topic and purpose of the lesson

Water is a universal solvent adapted to any kind of life activity. It dissolves almost any substance, in particular ionic and polar compounds. The unique impact properties are characterized by high dielectric constant. In nature, water contains a lot of substances and compounds that got into it one way or another.

Dissolution process

At first glance, the process of decay is simple, but its essence is much more complicated than it looks. That is why there are substances that are soluble in water and insoluble in other liquids. The creation of a solution is associated with physical processes: diffusion describes the very liquefaction of particles as a result of stirring. Hydration is the process by which chemical bonds are formed between water and an added substance.

The dissolution of substances is characterized by:

hydration that has occurred;
change in the color of the solution;
thermal effects (under certain conditions), etc. factors.

The proof of the mixing that has occurred is the change in the color of the solution. For example, an admixture of copper sulfate (which is initially white) turns water into an intense blue color. If the chemical properties of the bases are responsible for the color, then the release of heat is due to physical causes. Thus, it is a completely physical-chemical process.

What is a solution

Solution - homogeneous mixture solvent substances. Soluble substances decompose under the action of polar water molecules into small particles, as a result, mixing until completely homogeneous. Aqueous solutions are colorless and colored, but one thing is invariable - they are transparent, regardless of color.

It does not matter whether you add water to a substance or pour it. Also, the process will gradually occur and without intervention (stirring), in some cases a visible precipitate will form. In other cases, the solution is colored in the color of the added substance, but necessarily remains transparent to the light.

Undissolved substances settle to the bottom in a dense layer under water pressure. Or they can remain on the surface in the form of uneven particles. Liquids form layers because they have different densities with water. For example, vegetable oil forms a film on the surface.

Which substances are soluble in water and which are not?

Water is truly universal and unique in its properties. Sometimes it is necessary to mix more strongly to achieve complete destruction of the particles, but for the most part, water will erode any compounds. However, there are substances that are not subject even to her.

There is a condition according to which the amount of water must be greater so that the substances disperse, and not settle to the bottom. On the example of edible salt: when a large amount is added, it ceases to dissolve and forms a dense, stone-like layer.

In addition, some substances can be purified from the liquid, while others cannot. So, for example, mercury dissolves in water and the purification process is impossible. Other similar substances found in everyday life: table and sea salt, sugar of any type, baking soda, starch. They are invisible and tend to stain the water, but the particles are so small that they simply pass through the filtration along with the solution. Bulk substances like sand or clay do not dissolve, so the water can be filtered.

Classification of ability by substances:

Highly soluble (alcohol, sugar, salt (aka sodium), most alkalis and metal nitrates).
Slightly soluble (gypsum, berthollet salt, benzene, methane, nitrogen and oxygen).
Practically insoluble (precious and semi-precious metals, kerosene, a number of oils, inert gases, copper sulfide).

A separate group is fat-soluble and water-soluble vitamins. They are necessary for human health, and due to their ability to dissolve, they accumulate in the body due to the water content. The water-soluble type includes vitamins C, B1, B2, B3 (PP), B6, B12, folic acid, pantothenic acid and biotin.

Thus, water as a solvent is quite unique. The list of complex and insoluble substances is short enough to speak of the versatility of water as a solvent.

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The purpose of the lesson: study of the properties of water.

Lesson objectives: to give an idea of water as a solvent, of soluble and insoluble substances; introduce the concept of "filter", with the simplest ways to determine soluble and insoluble substances; prepare a report on the topic “Water is a solvent”.

Equipment and visual aids: textbooks, anthologies, notebooks for independent work; sets: glasses empty and with boiled water; boxes with table salt, sugar, river sand, clay; teaspoons, funnels, filters from paper napkins; gouache (watercolors), brushes and sheets for reflection; presentation made in Power Point, multimedia projector, screen.

DURING THE CLASSES

I. Organizational moment

U. Everyone Good morning! (Slide 1)
I invite you to the third meeting of the school science club "We and the world around us."

II. Message about the topic and purpose of the lesson

Teacher. Today we have guests, teachers from other schools who came to the meeting of the club. I propose to the chairman of the club, Poroshina Anastasia, to open the meeting.

Chairman. Today we have gathered for a club meeting on the topic “Water is a solvent”. The task for all those present is to prepare a report on the topic “Water is a solvent”. In this lesson, you will again become researchers of the properties of water. You will study these properties in your laboratories, with the help of "consultants" - Mikhail Makarenkov, Olesya Starkova and Yulia Stenina. Each laboratory will have to perform the following task: to conduct experiments and observations, and at the end of the meeting, discuss the plan for the message "Water - solvent".

III. Learning new material

U. With the chairman's permission, I would like to make the first announcement. (Slide 2) The same session on the topic “Water is a solvent” was recently held by students from the village of Mirny. The meeting was opened by Kostya Pogodin, who reminded everyone present of another amazing property of water: many substances in water can break down into invisible tiny particles, that is, dissolve. Therefore, water is a good solvent for many substances. After that, Masha proposed to conduct experiments and identify ways by which it would be possible to get an answer to the question of whether a substance dissolves in water or not.
U. I suggest that you at a club meeting determine the solubility in water of substances such as table salt, sugar, river sand and clay.
Let's assume which substance, in your opinion, will dissolve in water, and which will not. Express your assumptions, guesses and continue the statement: (Slide 3)

U. Let's think together what hypotheses we will confirm. (Slide 3)
Suppose ... (salt will dissolve in water)
Let's say ... (sugar will dissolve in water)
Perhaps ... (sand will not dissolve in water)
What if... (clay won't dissolve in water)
U. Come on, and we will conduct experiments that will help us figure it out. Before work, the chairman will remind you of the rules for conducting experiments and distribute cards on which these rules are printed. (Slide 4)
P. Look at the screen where the rules are written.

"Rules for conducting experiments"

All equipment must be handled with care. They can not only be broken, they can also get hurt.
During work, you can not only sit, but also stand.
The experiment is conducted by one of the students (the speaker), the rest silently observe or, at the request of the speaker, help him.
The exchange of opinions on the results of the experiment begins only after the speaker allows it to begin.
You need to talk to each other quietly, without disturbing the others.
Approaching the table and changing laboratory equipment is possible only with the permission of the chairman.

IV. Practical work

U. I suggest that the chairman choose a "consultant" who will read aloud from the textbook (p. 85) the procedure for conducting the first experiment. (Slide 5)

1) P. Spend experience with salt. Check if table salt dissolves in water.
A "consultant" from each laboratory takes one of the prepared sets and conducts an experiment with table salt. Boiled water is poured into a transparent glass. Pour a small amount of table salt into the water. The group observes what happens to the salt crystals and tastes the water.
The chairman (as in the KVN game) reads the same question to each group, and representatives from the laboratories answer them.
P.(Slide 6) Has the transparency of the water changed? (Transparency has not changed)
Has the color of the water changed? (Color has not changed)
Has the taste of water changed? (Water turned salty)
Can we say that the salt has disappeared? (Yes, she disappeared, disappeared, she is not visible)
U. Make a conclusion. (Salt dissolved)(Slide 6)

P. I ask everyone to proceed with the second experiment, for which it is necessary to use filters.
U. What is a filter? (A device, device or structure for purifying liquids, gases from solid particles, impurities.)(Slide 7)
U. Read aloud the procedure for performing the filter experiment. (Slide 8)
Students pass water with salt through a filter, observe and examine the taste of water.
P.(Slide 9) Is there any salt left on the filter? (There is no edible salt left on the filter)
Has the taste of water changed? (The taste of the water has not changed)
Have you been able to remove the salt from the water? (Table salt passed through the filter with water)
U. Make a conclusion from your observations. (Salt dissolved in water)(Slide 9)
U. Has your hypothesis been confirmed?
U. Everything is correct! Well done!
U. Write the results of the experiment in writing in the Notebook for independent work (p. 30). (Slide 10)

2) P.(Slide 11) Let's do the same experience again, but instead of salt, put a teaspoon granulated sugar.
A "consultant" from each laboratory takes a second set and runs an experiment with sugar. Boiled water is poured into a transparent glass. Pour a small amount of sugar into the water. The group observes what is happening and examines the taste of the water.
P.(Slide 12) Has the transparency of the water changed? (The transparency of the water has not changed)
Has the color of the water changed? (The color of the water has not changed)
Has the taste of water changed? (Water turned sweet)
Can we say that sugar is gone? (Sugar became invisible in water, water dissolved it)
U. Make a conclusion. (Sugar dissolved)(Slide 12)

U. Pass water with sugar through a paper filter. (Slide 13)
Students pass water with sugar through a filter, observe and examine the taste of water.
P.(Slide 14) Is there any sugar left on the filter? (Sugar is not visible on the filter)
Has the taste of water changed? (The taste of the water has not changed)
Have you managed to clear the water of sugar? (Water could not be purified from sugar, along with water it passed through the filter)
U. Make a conclusion. (Sugar dissolved in water)(Slide 14)
U. Has the hypothesis been confirmed?
U. Right. Well done!
U. Write the results of the experiment in writing in a notebook for independent work. (Slide 15)

3) P.(Slide 16) Let's check the statements and conduct river sand experience.
U. Read the procedure for conducting the experiment in the textbook.
Experiment with river sand. Stir a teaspoon of river sand in a glass of water. Let the mixture stand. Observe what happens to the grains of sand and water.
P.(Slide 17) Has the transparency of the water changed? (Water became cloudy, dirty)
Has the color of the water changed? (The color of the water has changed)
Are the grains gone? (Heavier grains of sand sink to the bottom, while smaller ones float in the water, making it cloudy)
U. Make a conclusion. (Sand didn't dissolve)(Slide 17)

U.(Slide 18) Pass the contents of the glass through a paper filter.
Students pass water with sugar through a filter, observe.
P.(Slide 19) What passes through the filter and what remains on it? (Water passes through the filter, but the river sand remains on the filter and the grains of sand are clearly visible)
Was the water cleared of sand? (The filter helps to clean the water of particles that do not dissolve in it)
U. Make a conclusion. (River sand did not dissolve in water)(Slide 19)
U. Was your assumption about the solubility of sand in water correct?
U. Great! Well done!
U. Write the results of the experiment in writing in a notebook for independent work. (Slide 20)

4) P.(Slide 21) Do the same experiment with a piece of clay.
Experiment with clay. Stir a piece of clay in a glass of water. Let the mixture stand. Observe what happens to clay and water.
P.(Slide 22) Has the transparency of the water changed? (Water turned cloudy)
Has the color of the water changed? (Yes)
Did the clay particles disappear? (Heavier particles sink to the bottom, while smaller ones float in the water, making it cloudy)
U. Make a conclusion. (Clay did not dissolve in water)(Slide 22)

U.(Slide 23) Pass the contents of the glass through a paper filter.
P.(Slide 24) What passes through the filter and what remains on it? (Water passes through the filter, and undissolved particles remain on the filter.)
Has the water been cleared of clay? (The filter helped clear the water of particles that didn't dissolve in the water)
U. Make a conclusion. (Clay does not dissolve in water)(Slide 24)
U. Has the hypothesis been confirmed?
U. Well done! Everything is correct!

U. I ask one of the group members to read the conclusions written in the notebook to all those present.
U. Does anyone have any additions or clarifications?
U. Let's draw conclusions from the experiments. (Slide 25)
Are all substances soluble in water? (Salt, granulated sugar dissolved in water, but sand and clay did not dissolve.)
Is it always possible to use a filter to determine whether a substance is soluble in water or not? (Substances dissolved in water pass through the filter along with water, while particles that do not dissolve remain on the filter)

U. Read about the solubility of substances in water in the textbook (p. 87).

U. Describe the property of water as a solvent. (Water is a solvent, but not all substances dissolve in it)(Slide 25)

U. I advise club members to read the story in the anthology "Water is a solvent" (p. 46). (Slide 26)
Why have scientists not yet been able to obtain absolutely pure water? (Because hundreds, maybe thousands of different substances are dissolved in water)

U. How do people use the property of water to dissolve certain substances?
(Slide 27) Tasteless water becomes sweet or salty due to sugar or salt, as water dissolves and acquires their taste. A person uses this property when preparing food: brews tea, cooks compote, soups, salts and preserves vegetables, prepares jam.
(Slide 28) When we wash our hands, wash or bathe, when we wash clothes, we use liquid water and its solvent property.
(Slide 29) Gases, in particular oxygen, also dissolve in water. Thanks to this, fish and others live in rivers, lakes, seas. In contact with air, water dissolves oxygen, carbon dioxide and other gases that are in it. For living organisms that live in water, such as fish, oxygen dissolved in water is very important. They need it to breathe. If oxygen did not dissolve in water, then water bodies would be lifeless. Knowing this, people do not forget to oxygenate the water in the aquarium where the fish live, or cut holes in the ponds in winter to improve life under the ice.
(Slide 30) When we paint with watercolors or gouache.

U. Pay attention to the task written on the board. (Slide 31) I propose to draw up a collective speech plan on the topic “Water is a solvent”. Discuss it in your laboratories.
Listening to plans on the topic “Water is a solvent” compiled by students.
U. Let's all come up with a plan together. (Slide 31)

Approximate speech plan on the topic “Water is a solvent”

Introduction.
Dissolution of substances in water.
Conclusions.
People use the property of water to dissolve certain substances.

Excursion to the "Exhibition Hall".(Slide 32)

U. When preparing a report, you can use additional literature selected by the guys, assistant speakers on the topic of our meeting. (Draw students' attention to the exhibition of books, Internet pages)

V. Summary of the lesson

What property of water was investigated at a club meeting? (Property of water as a solvent)
What conclusion did we come to by examining this property of water? (Water is a good solvent for some substances.)
Do you think it's hard to be explorers?
What seemed the most difficult, interesting?
Will the knowledge acquired during the study of this property of water be useful to you in later life? (Slide 33) (It is very important to remember that water is a solvent. Water dissolves salts, among which there are both beneficial and harmful to humans. Therefore, you cannot drink water from a source if you do not know whether it is pure. It is not in vain that people have Proverb: Not all water is good for drinking.

VI. Reflection

How do we use the property of water to dissolve certain substances in art classes? (When we paint with watercolors or gouache)
I suggest you, using this property of water, paint the water in a glass in a color that best suits your mood. (Slide 34)
"Yellow color" - joyful, bright, good mood.
"Green color" - calm, balanced.
"Blue color" - a sad, sad, dreary mood.
Show your sheets of colored water in a glass.

VII. Evaluation

I would like to thank the chairman, the "consultants" and all participants of the meeting for their active work.

VIII. Homework

The appearance of water on planet Earth is the first and most important step towards the emergence of life. And in the future, it continues to play the role of a substance, without which nothing living can exist. The reason for this is that water is a universal solvent in which all the most important biochemical processes of living organisms take place. This unique and versatile substance perfectly dissolves both organic and inorganic substances, oxidizes almost all metals and destroys the hardest rocks. All chemical processes proceed in water at a high speed, and the compounds formed in this process are very complex. Another unique property of water is that it remains liquid in a fairly large temperature range - from 0 to 100 ° C, and these are precisely the temperatures that are most often found on Earth.

In a word - if we were faced with the task of "pushing" the development of life on some planet, the first thing to do would be to create water.

Nowadays, scientists know more than 175 natural and artificially created varieties of water and about 200 varieties of ice. All of them have different, often extraordinary properties and affect the processes occurring in living organisms in different ways. The composition of this substance is almost always the same, but melted, spring, "magnetized", "alive" and "dead", ionized, "solid", "jelly-like", "rubber", "slippery", "dry", "viscous", "Epiphany" and many other types of water differ from each other sometimes even more than different chemical compounds.

If you add a tiny amount of special polymer compounds to water, it will become “slippery”: a steel ball in such water sinks to the bottom of the vessel 2.5 times faster than in ordinary water. Such water is indispensable for extinguishing fires.

Small doses of some silicon compounds make the water "dry". There is even "rubber" water, which, instead of pouring out of an inclined vessel, is drawn out in a dense elastic cord.

And one more amazing property of water - it has a "memory"! The structure of this substance is far from being as simple as it might seem at first glance. First, water molecules have both positive and negative electrical charges and are tiny “magnets” that can orient themselves in space in different ways. In addition, water molecules can form "communities" - they are called clusters. Such "communities", numbering several hundred molecules, turn water into a kind of polymer and contribute to the fact that water, as it were, "remembers" information about all the processes that have happened to it. The amount of "memory" of water far exceeds the memory capacity of the most sophisticated electronic storage devices created by man.

One of the manifestations of the “memory” of water is that it is able to retain the properties of a solution for some time even after not a single molecule of the solute remains in it.

Even today water is one of the biggest mysteries of nature. Man has dealt with it for thousands of years, but the structure of water has been revealed by science quite recently, and these studies are far from being completed. The main secret of water lies in the ability of its molecules to self-organize. Water clusters include up to 912 molecules, in addition, structures resembling crystal lattices, which include up to 57 molecules, can form in liquid water. Some clusters do not turn into ice even at temperatures below -150 °C. Thus, in water at any temperature, "organized" and "unorganized" parts simultaneously exist. This probably explains the diversity of its properties.

Water- the most common substance on Earth, it covers approximately four-fifths earth's surface. It is the only chemical compound that exists naturally as a liquid, solid (ice) and gas (water vapor). Water plays a vital role in industry, everyday life and in laboratory practice; it is absolutely necessary for the maintenance of life. Approximately two thirds human body are water, and many foods are made up primarily of water.

Structure and physical properties of water. IN 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. O-N connection covalent polar; angle--104.5°. Oxygen, as a more electronegative atom (electronegativity is the ability to attract the total electron density to itself when a bond is formed), pulls the electron density shared with the hydrogen atom towards itself And therefore carries a partial negative charge; hydrogen atoms, from which the electron density is shifted, carry a partial positive charge. So the water molecule is dipole, those. has positively and negatively charged regions. Water is a clear, colorless liquid with a number of anomalous properties. physical properties. For example, she has an abnormal high temperatures freezing and boiling, as well as 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 doesn't conduct well electricity, 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 has amphoteric properties. This means that it can act as both an acid and a base. Her amphoteric properties due to the ability of water to self-ionization:

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 oxidizer, as well as in the role reducing agent. It oxidizes metals located in the electrochemical series of voltages above tin. For example, in the reaction between sodium and water

the following oxidation process takes place:

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 that occur when iron rusts is as follows:

Water is an important reducing agent in biochemical processes. For example, some stages of the cycle citric acid include 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 successive chemical reactions. In both cases, the processes of electron transfer occurring in them have not yet been fully elucidated.

3.Hydration. Water molecules are capable of solvating both cations and anions. This process is called hydration. Hydrated water in salt crystals is called water of crystallization. Water molecules are usually associated with the cation they solvate by coordination bonds. The content of hydration water is indicated 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 reactions of this type would be the reaction between hydrogen chloride and water to form hydrochloric acid. Another example is the hydrolysis of iron(III) chloride:

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

6. Interaction with non-metal oxides: P 2 0 5 + H 2 0 \u003d 2HP0 3.

Water is widely used as a solvent in chemical

technology, as well as in laboratory practice. It is a universal solvent necessary for the occurrence of 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 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, we point out 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 raises 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 divided into temporary (carbonate, due to the presence of calcium bicarbonates Ca (HC0 3) 2

and magnesium Mg (NHOS) 2) and permanent (non-carbonate) rigidity. According to GOST R 52029-2003, hardness is expressed in degrees of hardness (° W), 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). Water is distinguished by the value of total hardness soft(up to 2 mg-eq/l), medium hardness(2-10 meq/l) and tough(more than 10 mg-eq/l).

The hardness of water from surface sources fluctuates significantly throughout the year; it is maximum at the end of winter, minimum - during the flood period (for example, the hardness of the Volga water in March is 4.3 mg-eq / l, in May - 0.5 mg-eq / l). In groundwater, the hardness is usually higher (up to 80–100 mg-eq/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 gas concentration in the liquid.

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

1) the process of destruction of the crystal lattice. This process requires energy, so 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 an increase and a decrease in temperature.

Solution is called a homogeneous (homogeneous) system consisting of two or more components. The essential components of a solution are a solvent and a solute, such as sugar dissolved in water. A single solvent can contain several solutes. For example, when preparing a marinade, sugar, salt and acetic acid are dissolved in water. Solutes with the same aggregate state of the components, the components that are in short supply are usually considered, while the component that is in excess is considered solvent. With different aggregate states of the solution components, the solvent is usually considered to be a component whose aggregate state coincides with the aggregate state of the solution. For example, in the case of liquid solutions of solids and gases, the solvent is always considered to be the liquid component, regardless of the concentration of the solutes. If two liquids are used in preparing a solution, the solvent is the one in excess. If water is used in the preparation of the solution, then the solvent is water.

Water is one of the most common compounds on earth. It is not only in rivers and seas; All living organisms also contain water. Life is impossible without it. Water is a good solvent (different substances dissolve easily in it). Animals and plant sap are composed primarily of water. Water exists forever; it is constantly moving from the soil to the atmosphere and organisms and vice versa. More than 70% of the earth's surface is covered with water.

What is water

The water cycle

The water of rivers, seas, lakes constantly evaporates, turning into tiny drops of water vapor. The drops gather together to form, from which the water falls to the ground in the form of rain. This is the water cycle in nature. In the clouds, the vapor cools and returns to earth in the form of rain, snow or hail. Wastewater from sewers and factories is treated and then dumped into the sea.

Water station

River water necessarily contains impurities, so it must be purified. Water enters the reservoirs, where it settles and solid particles settle to the bottom. The water then passes through filters that trap any remaining solids. Water percolates through layers of clean gravel, sand, or activated carbon where it is cleaned of dirt and solid impurities. After filtration, the water is treated with chlorine to kill pathogenic bacteria, after which it is pumped into tanks and fed to residential buildings and factories. Before waste water goes to sea, it needs to be cleaned. At the water treatment plant, it is passed through filters that trap dirt, then pumped to septic tanks, where solid particles must settle to the bottom. Bacteria destroy the remains of organic substances, decomposing them into harmless components.

Water purification

Water is a good solvent, so it usually contains impurities. You can purify water with distillation(see article ""), but more effective method cleaning - deionization(desalting). Ions are atoms or molecules that have lost or gained electrons and, as a result, have received a positive or negative charge. For deionization, a substance called ion exchanger. It has positively charged hydrogen ions (H +) and negatively charged hydroxide ions (OH -) When contaminated water passes through the ion exchanger, the impurity ions are replaced by hydrogen and hydroxide ions from the ion exchanger. Hydrogen and hydroxide ions combine to form new water molecules. Water that has passed through the ion exchanger no longer contains impurities.

Water as a solvent

Water is an excellent solvent, many substances dissolve easily in it (see also the article ""). That is why pure water is rarely found in nature. In a water molecule, the electric charges are slightly separated, since the hydrogen atoms are located on one side of the molecule. Because of this, ionic compounds (compounds made up of ions) dissolve so easily in it. Ions are charged and water molecules attract them.

Water, like all solvents, can only dissolve a limited amount of a substance. A solution is called saturated when the solvent cannot dissolve an additional portion of the substance. Typically, the amount of a substance that a solvent can dissolve increases with heat. Sugar dissolves more easily in hot coda than in cold coda. Effervescent drinks are aqueous carbon dioxide diffusers. The higher the large quantity gas is able to absorb the solution. Therefore, when we open a can of a drink and thereby reduce the pressure, carbon dioxide escapes from the drink. When heated, the solubility of gases decreases. In 1 liter of river and sea water, about 0.04 grams of oxygen is usually dissolved. This is enough for algae, fish and other inhabitants of the seas and rivers.

hard water

Hard water contains minerals from rocks through which water flows. In such water, soap does not lather well, because it reacts with minerals and forms flakes. There are two types of hard water; the difference between them is in the type of dissolved minerals. The type of minerals dissolved in water depends on the type of rocks through which the water flows (see figure). Temporary hardness of water occurs when limestone reacts with rainwater. Limestone is an insoluble calcium carbonate and rainwater is a weak solution of carbonic acid. The acid reacts with calcium carbonate to form bicarbonate, which dissolves in water and hardens it.

When water boils or evaporates with temporary hardness, some of the minerals precipitate, forming scale at the bottom of the kettle or stalactites and stalagmites in the cave. Water with constant hardness contains other calcium and magnesium compounds, such as gypsum. These minerals do not precipitate when boiled.

Water softening

You can remove the minerals that make water hard by adding washing soda to the solution or by ion exchange, a process similar to the deionization of water during purification. A substance containing sodium ions that are exchanged with calcium and magnesium ions in water. In an ion exchanger, hard water passes through zeolite- a substance containing sodium. In zeolite, calcium and magnesium ions are mixed with sodium ions, which do not give water hardness. Washing soda is sodium carbonate. In hard water, it reacts with calcium and magnesium compounds. The result is insoluble compounds that do not form flakes.

Water pollution

When untreated water from factories and homes enters the seas and rivers, water pollution occurs. If there is too much waste in the water, organic-decomposing bacteria multiply and consume almost all of the oxygen. In such water, only pathogenic bacteria that can live in water without oxygen survive. When the level of dissolved oxygen in the water decreases, fish and plants die. Garbage, pesticides and nitrates from fertilizers also get into the water, poisonous ones - lead, mercury. Poisonous substances, including metals, enter the body of fish, and from them - into the bodies of other animals and even humans. Pesticides kill microorganisms and animals, thereby disturbing the natural balance. Fertilizers from the fields and detergents containing phosphates, getting into the water, cause increased plant growth. Plants and bacteria that feed on dead plants take up oxygen, reducing its content in the water.

Brief description of the role of water for organisms

Water is the most important inorganic compound, without which life is impossible on. This substance is also the most important part, and plays a large role as an external factor for all living beings.

On planet Earth, water is found in three states of aggregation: gaseous (vapors in, liquid (water in and foggy in the atmosphere) and solid (water in glaciers, icebergs, etc.). The formula of vaporous water is H 2 O, liquid (H 2 O) 2 (at T \u003d 277 K) and (H 2 O) n - for solid water (ice crystals), where n \u003d 3, 4, ... (depends on temperature - the lower the temperature, the greater the value of n). Water molecules combine into particles with the formula (H 2 O) n as a result of the formation of special chemical bonds called hydrogen; such particles are called associates; due to the formation of associates, looser structures arise than liquid water, therefore, at a temperature below 277 K, the density of water, unlike other substances, it does not increase, but decreases, as a result, ice floats on the surface of liquid water and deep reservoirs do not freeze to the bottom, especially since water has low thermal conductivity.This is of great importance for organisms living in water - they do not die in severe frosts and survive during the winter cold until more favorable temperature conditions.

The presence of hydrogen bonds determines the high heat capacity of water, which makes life possible on the surface of the Earth, since the presence of water helps to reduce the temperature difference day and night, as well as in winter and summer, because when cooled, water condenses and heat is released, and when heated, water evaporates, on the breaking of hydrogen bonds is spent and the Earth's surface does not overheat.

Water molecules form hydrogen bonds not only among themselves, but also with molecules of other substances (carbohydrates, proteins, nucleic acids), which is one of the reasons for the formation of the complex chemical compounds, as a result of the formation of which the existence of a special substance is possible - a living substance that forms various.

The ecological role of water is enormous and has two aspects: it is both an external (first aspect) and an internal (second aspect) environmental factor. Like external environmental factor water is part of abiotic factors (humidity, habitat, component climate and microclimate). As an internal factor, water plays an important role inside the cell and inside the body. Consider the role of water inside the cell.

In the cell, water performs the following functions:

1) the environment in which all the organelles of the cell are located;

2) a solvent for both inorganic and organic substances;

3) environment for the occurrence of various biochemical processes;

4) a catalyst for exchange reactions between inorganic substances;

5) reagent for the processes of hydrolysis, hydration, photolysis, etc.;

6) creates a certain state of the cell, such as turgor, which makes the cell elastic and mechanically strong;

7) performs a building function, consisting in the fact that water is part of various cellular structures, such as membranes, etc.;

8) is one of the factors that unite all cellular structures into a single whole;

9) creates an electrical conductivity of the medium, converting inorganic and organic compounds into a dissolved state, causing electrolytic dissociation of ionic and highly polar compounds.

The role of water in the body is that it:

1) performs a transport function, since it converts substances into a soluble state, and the resulting solutions due to various forces (for example, osmotic pressure, etc.) move from one organ to another;

2) performs a conductive function due to the fact that the body contains electrolyte solutions capable of conducting electrochemical impulses;

3) binds together individual bodies and organ systems due to the presence of special substances (hormones) in the water, while carrying out humoral regulation;

4) is one of the substances that regulate the body temperature of the body (water in the form of sweat is released to the surface of the body, evaporates, due to which heat is absorbed and the body cools down);

5) is part of food products etc.

The significance of water outside the body is described above (habitat, environmental temperature regulator, etc.).

For organisms, fresh water plays an important role (salt content less than 0.3%). In nature, chemically pure water practically does not exist, the most pure is rainwater from rural areas, remote from large settlements. Water contained in fresh water bodies - rivers, ponds, fresh lakes - is suitable for organisms.