Objective: To learn by experience which solids dissolve in water and which do not dissolve in water.

Educational:

• To acquaint students with the concepts: soluble and insoluble substances.
• Learn to prove empirically the correctness of the assumptions about the solubility (insolubility) of solids.

Corrective:

Learn how to use laboratory equipment and conduct experiments.

• Develop speech through the explanation of the work being done.

Educational:

Cultivate perseverance.

• Develop the ability to communicate and work in groups.

Type of lesson: laboratory work.

Teaching aids: textbook "Natural science" N.V. Koroleva, E.V. Makarevich

Equipment for laboratory work: beakers, filters, instructions. Solids: salt, sugar, soda, sand, coffee, starch, earth, chalk, clay.

During the classes

I. Organizational moment

W: Hello guys. Greet each other with your eyes. Nice to see you, have a seat.

. Repetition of the past

T: Let's repeat what we already know about water:

What happens to water when heated?
What happens to water when it cools?
What happens to water when it freezes?
What are the three states in which water occurs in nature?

W: What good fellows you are! Everyone knows!

III. Learning new material

(I agree with the students in advance on the groups they will work with, the guys themselves choose the head of the laboratory (another child can be selected at another laboratory lesson), who writes the experience indicators in a table and gives oral comments when filling out the final part of the table - the result.)

U: Guys, today in the laboratory work we will find out which substances water can dissolve and which cannot. Open a notebook, write down the date and the topic of the lesson “Soluble and insoluble substances in water”. ( I'm attaching to the board.) What is the goal of today's lesson?

R: Find out which substances dissolve in water and which do not. ( I'm attaching to the board.)

U: All substances in nature can be divided into two groups: soluble and insoluble. What substances can be called soluble? (Check textbook p.80:2) Water-soluble substances are those that, when placed in water, become invisible and do not settle on the filter during filtration.. (Attached to the board.)

T: And what substances can be named insoluble? (check textbook p.47-2) Water-insoluble substances - those that do not dissolve in water and settle on the filter (attach to the board).

T: Guys, what do you think we need to complete the laboratory work?

R: Water, some substances, beakers, filter ( I show the water in the decanter; beakers filled with substances: salt, sugar, soda, sand, coffee, starch, chalk, clay; empty beakers, filter).

Q: What is a filter?

R: A device for purifying liquids from substances insoluble in it that settle on it.

U: And what improvised means can be used to make a filter? Well done! And we will use cotton wool ( I put a piece of cotton in the funnel).

U: But before starting the laboratory work, let's fill in the table (the table is drawn on the blackboard, I use two colors of crayons, if the students assume that the substance is completely soluble in water, then I mark "+" in the second column; if the students assume that the substance remains on the filter, then “+” in the third column, and vice versa; with colored chalk I fix the expected result in the fourth column - P (soluble) or H (insoluble))

	Our Assumptions		Result
	Solubility	Filtration
1. Water + sand	–	+	H
2. Water + clay
3. Water + coffee
4. Water + starch
5. Water + soda
6. Water + earth
7. Water + sugar
8. Water + chalk

U: And after doing the laboratory work, we will compare our assumptions with the results obtained.

T: Each lab will test two solids, all results will be recorded in the report “Soluble and insoluble substances in water”. Appendix 1

U: Guys, this is your first independent laboratory work and before you start doing it, listen to the procedure or instructions. ( I distribute to each laboratory, after reading we discuss.)

Laboratory work

(I help if necessary. It may be difficult to filter the coffee solution, because the filter will be stained. To facilitate filling out the reports, I suggest using the phrases that I attach to the board. Annex 3.)

T: Now let's check our assumptions. Heads of laboratories, check if your report is signed and comment on the results obtained by experience. (The head of the laboratory reports, fixing the result with a piece of chalk of a different color)

U: Guys, what substances for research turned out to be soluble? What are not? How many matches were there? Well done. Almost all of our assumptions were confirmed.

VI. Questions for consolidation

U: Guys, where does a person use a solution of salt, sugar, soda, sand, coffee, starch, clay?

VII. Lesson summary

T: What is our goal today? Did you complete it? Are we great? I am very satisfied with you! And I give everyone "excellent".

VIII. Homework

T: Read the text for extracurricular reading on page 43, answer the questions.

Stand up, please, those guys who did not like our lesson. Thank you for your honesty. And now those who liked our work. Thank you. Goodbye everyone.

The fact that water is an excellent solvent, we all know since childhood. But what "magical action" occurs at the moment when water is added to this or that substance? And why, if this solvent is considered universal, are there still those substances - “white crows” that water will never be able to do?

The secret is simple but brilliant. The water molecule itself is electrically neutral. However, the electric charge inside the molecule is distributed very unevenly. The area of ​​hydrogen atoms has a positively tuned "character", and the "residence" of oxygen is famous for its expressive negative charge.

If the energy of attraction of water molecules to the molecules of a substance prevails compared to the energy of attraction between water molecules, then the substance dissolves. If such a condition is not met, then the “miracle” also, respectively, does not occur.

The main "traffic light" with a lit red color for water is fats. That is why, if we suddenly “reward” clothes with an expressive oily stain, the phrase “Just add water” in this situation will not be saving.

Although, due to the fact that we are subconsciously accustomed to seeing water as a universal solvent, which practically can handle any problem, we often still try to solve the problem with water. And when nothing works out for us, then most often we get angry, but in fact, we should ... rejoice. Yes, just rejoice!

Indeed, for the reason that water is unable to dissolve fats, we can ... live. Because it is precisely due to the fact that fats are included in the “black list” for water that we ourselves do not dissolve.

But salts, alkalis and acids for water are a real “delicacy”. By the way, such Chemical properties again, they are very much in the hands of a person. After all, if this were not so, then the decay products would create a real dump in the body, and the blood would automatically thicken. Therefore, if a person is deprived of water, then on the 5th day he dies. In addition, of course, if you do not regularly receive the required amount (the "average" norm is 2-3 liters per day), undissolved salts significantly increase the risk of kidney stones, as well as the bladder.

However, of course, it is precisely because water dissolves, for example, the same salts that it is not worth turning into an uncontrolled “water drink”, setting impudent “records”, simply because some dispute has obliged it. After all, this can greatly disrupt the mineral balance of the body.

By the way, passing through oneself (both literally and figuratively) and understanding the physical and chemical essence of this phenomenon, it is easy to understand the role of water as a solvent in many other areas of both domestic and industrial plans.

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 her. Water is a good solvent (it dissolves easily different substances). 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 electric charges 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 more gas the solution can absorb. Therefore, when we open a can of a drink and thereby reduce the pressure, the drink escapes carbon dioxide. 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

Minerals are dissolved in hard water, which got there from the rocks through which the water flowed. In such water, soap does not lather well, because it reacts with minerals and forms flakes. There are two kinds 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 minerals that make water hard by adding washing soda to the solution or by ion exchange, a process similar to deionizing 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, the bacteria that decompose organic matter, multiply and absorb almost all 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. Toxic substances, including metals, enter the body of fish, and from them - into the organisms 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 (vapours 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 liquid water and deep reservoirs do not freeze to the bottom, especially since water has low thermal conductivity. It has great importance for organisms living in water, they do not die during severe frosts and survive during the winter cold until more favorable temperature conditions occur.

Availability hydrogen bonds causes a high heat capacity of water, which makes possible life 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, it is spent on breaking hydrogen bonds 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. As an external environmental factor, water is part of abiotic factors (humidity, habitat, an integral part of 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, transferring inorganic and organic compounds into a dissolved state, causing electrolytic dissociation 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 organs and organ systems due to the presence of special substances (hormones) in 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.).

plays an important role in organisms fresh water(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.

The most common solvent on our planet is water. The body of an average person weighing 70 kg contains approximately 40 kg of water. At the same time, about 25 kg of water falls on the fluid inside the cells, and 15 kg is extracellular fluid, which includes blood plasma, intercellular fluid, cerebrospinal fluid, intraocular fluid and liquid contents of the gastrointestinal tract. In animal and plant organisms, 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 ionic and many polar compounds well. This property of water is largely due to its high dielectric constant (78.5).

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

Since water is the main part internal environment organism, 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 the biological oxidation of substances, in particular glucose. The formation of water as a result of these processes is accompanied by the release a large number energy approximately 29 kJ/mol.

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

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

Depending on their affinity for water, the functional groups of dissolved particles are divided into hydrophilic (attracting water), easily solvated by water, hydrophobic (repelling water), and amphiphilic.

To hydrophilic groups polar functional groups include: hydroxyl -OH, amino -NH 2, thiol -SH, carboxyl -COOH.

To hydrophobic - non-polar groups, for example, hydrocarbon radicals: CH3-(CH 2) p -, C 6 H 5 -.

Amino acids include substances (amino acids, proteins) whose molecules contain both hydrophilic groups (-OH, -NH 2, -SH, -COOH) and hydrophobic groups: (CH 3, (CH 2) p, - C 6 H 5 -).

When amphiphilic substances are dissolved, the structure of water changes as a result of interaction with hydrophobic groups. The degree of ordering of water molecules close to hydrophobic groups increases, and the contact of water molecules with hydrophobic groups is minimized. Hydrophobic groups, associating, push water molecules out of their area of ​​location.

Dissolution process

The nature of the dissolution process is complex. Naturally, the question arises why some substances are easily soluble in some solvents and poorly soluble or practically insoluble in others.

The formation of solutions is always associated with certain physical processes. One such process is the diffusion of a solute and a solvent. Due to diffusion, particles (molecules, ions) are removed from the surface of the dissolved substance and are evenly distributed throughout the volume of the solvent. That is why, in the absence of stirring, the dissolution rate depends on the diffusion rate. However, it is impossible to explain the unequal solubility of substances in various solvents only by physical processes.

The great Russian chemist D. I. Mendeleev (1834-1907) believed that chemical processes play an important role in dissolution. He proved the existence of sulfuric acid hydrates H 2 SO 4 * H 2 O, H 2 SO 4 * 2H 2 O, H 2 SO 4 * 4H 2 O and some other substances, for example, C 2 H 5 OH * 3H 2 O. V In these cases, the dissolution is accompanied by the formation of chemical bonds between the particles of the solute and the solvent. This process is called solvation, in the particular case when the solvent is water, hydration.

As established, depending on the nature of the solute, solvates (hydrates) can be formed as a result of physical interactions: ion-dipole interaction (for example, when dissolving substances with an ionic structure (NaCI, etc.); dipole-dipole interaction when dissolving substances with a molecular structure (organic substances) ).

Chemical interactions are carried out due to donor-acceptor bonds. Here, solute ions are electron acceptors, and solvents (H 2 O, NH 3) are electron donors (for example, the formation of aqua complexes), and also as a result of the formation of hydrogen bonds (for example, the dissolution of alcohol in water).

Evidence chemical interaction solute with a solvent are the thermal effects and color change accompanying the dissolution.

For example, when potassium hydroxide is dissolved in water, heat is released:

KOH + xH 2 O = KOH (H 2 O) x; ΔH° solution = 55 kJ/mol.

And when sodium chloride is dissolved, heat is absorbed:

NaCI + xH 2 O = NaCI (H 2 O) x; ΔН° solution = +3.8 kJ/mol.

The heat released or absorbed when 1 mole of a substance is dissolved is called heat of dissolution Q sol

According to the first law of thermodynamics

Q solution = ΔH solution ,

where ΔН sol is the change in enthalpy upon dissolution of a given amount of a substance.

Dissolution of anhydrous copper sulfate in water white color results in an intense blue color. The formation of solvates, color change, thermal effects, as well as a number of other factors, indicate a change in the chemical nature of the components of the solution during its formation.

Thus, in accordance with modern concepts, dissolution is a physicochemical process in which both physical and chemical species interactions.

Water is a liquid substance that has no taste, color or smell. Pure water is absolutely transparent. If you pour water into a glass, you can see objects behind it through its walls. Water has fluidity thanks to which it penetrates through cracks and crevices, impregnates everything around.

Liquid water:

• fills the seas, oceans, rivers and lakes;
• impregnates the soil;
• is part of plants;
• is part of the bodies of mammals.

The amazing property of water is that it can dissolve almost everything around. There are some items that get wet but remain undissolved. How and why is this happening?

What is a solution?

When a substance dissolves, it mixes with the liquid to form a solution. The solution can be called tea in a glass, Where did you put a piece of sugar before. Sugar-absorbed water becomes sweet in taste. When a substance combines with a solvent, a solution is formed. Water solution is a water-soluble substance that has been diluted with pure water. Water is a good solvent, but it cannot dissolve stone, wood, plastic. If you throw a few pebbles into the water, they will remain lying at the bottom of the glass.

How does this happen?

If we examine a drop of water under a microscope, we will see that it consists of special particles called molecules. They cannot be seen with the naked eye. Water molecules are electrically neutral this means that they are "friends" with all substances. For some substances, they experience a special attraction. The amazing friendliness of water molecules allows them to easily combine with molecules of other substances, carrying a charge.

In contact with the molecules of another substance, attraction increases, as a result, the substance mixes with water, completely dissolving in it. If there is no attraction, then accordingly, everything remains unchanged. The substance will remain at the bottom of the glass. If you add a little salt to the water and stir with a spoon, the salt will soon disappear. The water will taste salty.

What is pure water?

Absolutely pure water does not exist in nature. Almost all the liquids that we see in Everyday life, are solutions. Tap water is a solution of water with iron impurities. Before entering the glass, water flows through iron pipes, absorbing iron molecules. Natural solutions are drinks - tea, juice and compotes. All of them contain components useful for the human body. Water can dissolve not only solid, but liquid and gaseous substances.

In ordinary water, something is always dissolved. In rain, water, river or lake - contain any impurities.

Which substances dissolve in water and which do not?

In nature, there are solid, liquid and gaseous substances endowed with various properties. Some of them are able to dissolve in water, others are not. Depending on this feature, the following groups of substances are distinguished:

• water-repellent (hydrophobic);
• attract water (hydrophilic).

Hydrophobic substances are either poorly soluble in water or do not dissolve in it at all. Such substances include rubber, grease, glass, sand, etc. Some salts, alkalis and acids can be called hydrophilic substances.

Since the cells of the human body contain a membrane containing fatty components, fat does not allow the human body to dissolve in water. Due to the unique structure of a living organism, water not only does not absorb body cells, but also supports human life.

Summing up

When in contact with food, water dissolves nutrients, and then gives them to the cells of the human body. In return, water takes away waste products that come out with sweat and urine.

There are few substances in nature that do not dissolve in water. Even metal, upon prolonged contact with water, begins to dissolve in it.

Water with dissolved components acquires new qualities. For example, a solution of silver is able to kill microbes. Water is a system that can be beneficial or harmful to humans. And it depends on what is dissolved in it.

If this message was useful to you, I would be glad to see you