Water as a solvent for various substances. Water. Properties and significance of water for living organisms. III. Learning new material
(H2O) is one of the most common and important substances. There is no pure water in nature - it always contains impurities. Pure water is obtained by distillation. Distilled water is called distilled water. Water composition (by weight): 11.19% hydrogen and 88.81% oxygen. Pure water is clear, odorless and tasteless. It has the highest density at 0 ° C (1 g / cm3). The density of ice is less than that of liquid water, so the ice floats to the surface. Water freezes at 0 ° C and boils at 100 ° C at a pressure of 101,325 Pa. It conducts heat poorly and conducts electricity very poorly. Water is a good solvent. The water molecule has an angular shape; hydrogen atoms form an angle of 104.3 ° with respect to oxygen. Therefore, a water molecule is a dipole: that part of the molecule where hydrogen is located is positively charged, and the part where oxygen is located is negative. Due to the polarity of water molecules, electrolytes in it dissociate into ions. Along with ordinary H2O molecules, liquid water contains associated molecules, that is, they are connected into more complex aggregates (H2O) x due to the formation of hydrogen bonds (Fig. 4). The presence of hydrogen bonds between water molecules explains the anomalies of its physical properties: maximum density at 4 ° C, high boiling point (in the series Н2О - Н2S - Н2Sе), anomalously high heat capacity (4.18 kJ / (g K)). With an increase in temperature, hydrogen bonds are broken, and a complete rupture occurs when water passes into steam.
Figure 4. Water molecule
Solutions are a homogeneous multicomponent system consisting of a solvent, solutes and products of their interaction. According to the state of aggregation, solutions can be liquid (sea water), gaseous (air), or solid (many metal alloys). Particle sizes in true solutions are less than 10-9 m (on the order of molecular sizes). If molecular or ionic particles distributed in a liquid solution are present in it in such an amount that under these conditions no further dissolution of the substance occurs, the solution is called saturated. (For example, if you put 50 g of NaCl in 100 g of H2O, then at 200C only 36 g of salt will dissolve).
Saturated is a solution that is in dynamic equilibrium with an excess of solute. By placing less than 36 g of NaCl in 100 g of water at 200C, an unsaturated solution is obtained. When a mixture of salt and water is heated to 1000C, 39.8 g of NaCl will dissolve in 100 g of water. If now the undissolved salt is removed from the solution and the solution is carefully cooled to 200C, the excess amount of salt does not always precipitate. In this case, we are dealing with a supersaturated solution. Supersaturated solutions are very unstable. Stirring, shaking, adding grains of salt can cause crystallization of excess salt and a transition to a saturated stable state. Unsaturated solution - a solution containing less substance than saturated. Supersaturated solution - a solution containing more substance than saturated solution.
Solutions are formed by the interaction of a solvent and a solute. The process of interaction between a solvent and a solute is called solvation (if the solvent is water, hydration). Dissolution proceeds with the formation of products of various shapes and strengths - hydrates. This involves forces of both physical and chemical nature. The dissolution process due to this kind of interactions of the components is accompanied by various thermal phenomena. The energy characteristic of dissolution is the heat of formation of the solution, considered as the algebraic sum of the heat effects of all endo- and exothermic stages of the process. The most significant among them are:
- heat absorbing processes - destruction of the crystal lattice, breaking of chemical bonds in molecules;
- heat-generating processes - the formation of products of the interaction of a solute with a solvent (hydrates), etc.
If the energy of destruction of the crystal lattice is less than the hydration energy of the solute, then dissolution proceeds with the release of heat (heating is observed). So, the dissolution of NaOH is an exothermic process: 884 kJ / mol is spent on the destruction of the crystal lattice, and 422 and 510 kJ / mol are released during the formation of hydrated Na + and OH - ions, respectively. If the energy of the crystal lattice is greater than the energy of hydration, then dissolution proceeds with the absorption of heat (when preparing an aqueous solution of NH4NO3, a decrease in temperature is observed).
Solubility. The limiting solubility of many substances in water (or in other solvents) is a constant value corresponding to the concentration of a saturated solution at a given temperature. It is a qualitative characteristic of solubility and is given in reference books in grams per 100 g of solvent (under certain conditions). Solubility depends on the nature of the solute and solvent, temperature and pressure.
1. The nature of the solute. Crystalline substances are classified into:
P - highly soluble (more than 1.0 g per 100 g of water);
M - slightly soluble (0.1 g - 1.0 g per 100 g of water);
H - insoluble (less than 0.1 g per 100 g of water).
2. The nature of the solvent. When a solution is formed, bonds between particles of each of the components are replaced by bonds between particles of different components. For new bonds to form, the components of the solution must have the same type of bonds, i.e., be of the same nature. Therefore, ionic substances dissolve in polar solvents and poorly in non-polar ones, while molecular substances do the opposite.
3. Influence of temperature. If the dissolution of a substance is an exothermic process, then with an increase in temperature, its solubility decreases (for example, Ca (OH) 2 in water) and vice versa. Most salts are characterized by an increase in solubility on heating (Fig. 5). Almost all gases dissolve with the release of heat. The solubility of gases in liquids decreases with increasing temperature, and increases with decreasing.
4. Influence of pressure. With increasing pressure, the solubility of gases in liquids increases, and decreases with decreasing.
Figure 5. Dependence of solubility of substances on temperature
2nd grade student
Empirically, it was possible to find out that water is a solvent of many substances, therefore it is necessary for living of living beings.
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Municipal budgetary educational institution
"Klyuevskaya secondary school"
“Water is like a solvent,
water dissolution value "
Completed: 2nd grade student
Supervisor: primary school teacher
Paderina Olga Nikolaevna
from. Klyuevka
2018
Introduction
“… You have no taste, no color, no smell, you cannot be described, you are enjoyed without knowing what you are? This is not to say that you are necessary for life: you are life itself. You fill us with joy ... You are the greatest wealth in the world ... "
Antoine de Saint-Exupery
Project: "Water - as a solvent, the meaning of water dissolution"
Objective of the project: Find out if water is a solvent
Project objectives:
1) conduct an experiment and draw a conclusion about water as a solvent for substances;
2) learn to work independently with various sources of information;
3) to foster love for nature, respect for it.
Object of study: water.
Subject of study: the property of water is solubility.
Hypotheses:
Suppose ... (salt dissolves in water)
Let's say ... (sugar dissolves in water)
Perhaps ... (the sand will not dissolve in water)
What if ... (chalk does not dissolve in water)
Main part
What do we know about water?
Take a look at the world map.
Most of all it has blue paint. And the blue color on the maps depicts water, without which no one can ever do, and there is nothing to replace it with.
Water occupies 3/4 of the earth's surface. Water is everywhere. A thick layer of air covers the entire globe with a continuous shell. And there is a lot of water, steam, clouds, clouds in the air.
Water is a part of any living organism. It is enough to crumple a leaf of a plant in your hands, and we will find moisture in it. Water is found in all parts of plants. In the body of animals, water is more than half the mass.
Water is one of the most important substances for humans. Loss of water for the body is more dangerous than starvation. A person can live without food for more than a month, and without water, less than 10 days.
Fields and forests drink water. Birds and animals cannot live without it. Water works in power plants. But the water not only gives water to people, but also feeds them - ships sail by day and night and carry cargo across the seas and oceans. Water is also a road for transporting passengers. You cannot make bread, paper, rubber, cloth, candy, medicine without water - nothing can be done without water.
And what do grade 2 students know about the properties of water?
The students were asked to answer several questions about the properties of water. 22 people were interviewed
The survey results are presented in the table.
Question | Answer | Number of persons |
What is the color of the water? |
| 20 pax 2 pax |
Can I change the color of the water? |
| 19 pax 2 pax 1 person |
Can water dissolve substances? |
| 12 pax 10 pax |
How long can a person go without water? |
| 5 pax 15 pax 2 pax |
Analysis of the questionnaires showed that the majority of grade 2 students (10 people) find it difficult to choose an answer to the question: "Can water dissolve substances?" Therefore athe relevance of our of the project consists in the opportunity in practice to acquaint everyone with one of the main properties of water - solubility, to find out how much this property is necessary for every living being, what property of water does a person use when washing dishes, washing clothes, washing himself?
Many people think that they know water well. After all, everyone wash every day, drink water, often watch how it rains, how the river flows. But it turns out that everything is not so simple in nature. There are still many secrets in it. Scientists are trying to figure them out. And we will start with a simple one: we will investigate the solubility of water in school conditions.
Let's use experience to open the veil of the mystery of water.
The purpose of the experiment: show that water is a solvent.
Experience number 1:
In a glass of drinking water, I put 1 teaspoon of salt, mixed the water for 1 minute, noticed that the water is clear, tasted salty, which means the salt has dissolved. Water is a solvent.
Experience number 2:
I put 1 teaspoon of sugar in a glass of drinking water, mixed the water for 1 minute, noticed that the water is clear, the taste has become sweet, which means the sugar has dissolved. Conclusion: water is a solvent.
Experience number 3:
I put 1 spoonful of sand in a glass of drinking water, stirred the water for 1 minute, noticed that the water became dirty, cloudy, after standing for a while, a sediment appeared at the bottom, which means the sand did not dissolve. Conclusion: water does not dissolve all substances.
Experience number 4:
In a glass of drinking water, I put 1 spoonful of crushed chalk, mixed the water for 1 minute, noticed that the water turned white, after standing for a while, the chalk settled to the bottom, a precipitate appeared, which means the chalk did not dissolve.
Conclusion: water does not dissolve all substances.
Output: water is a solvent, but not all substances dissolve in it.
Conclusion
Empirically, it was possible to find out that water is a solvent of many substances, therefore it is necessary for living of living beings.
Organisms of animals and plants contain from 50 to 90% water. In the human body, water makes up about 65% of the body weight. The loss of more than 10% of water by the human body can lead to death. With a life expectancy of 70 years, a person consumes 25 tons of water. We learned this from the textbook and other scientific literature.
Even gold, silver, iron, glass dissolve in water to an insignificant degree. Due to the ability of water to dissolve other substances, it can never be called absolutely pure. The concept of "clean" water is conditional.
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, in particular, by astronauts during their flights.
Not only solid and liquid substances dissolve in water, but also gases, for example, fish, as well as other animals and plants, breathe oxygen dissolved in water. 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 through the plant in the form of solutions, for seed germination.
Our hypothesis was confirmed: withol, sugar dissolve in water, chalk and sand do not dissolve in water. This means that solubility is an important property of water.
Have you heard of water? They say she is everywhere!
In a puddle, in the sea, in the ocean, and at the tap.
Like an icicle, it freezes, creeps into the forest with fog,
It is called a glacier in the mountains, it winds like a silver ribbon.
We are used to the fact that water is always our companion!
Without her, we cannot wash, not eat, not get drunk.
I dare to report to you: we cannot live without her!
THANKS FOR ATTENTION!
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. Many salts, acids and bases are soluble in water from inorganic substances. Of organic substances, only those are soluble in the molecules of which polar groups constitute a significant part - many alcohols, amines, organic acids, sugars, etc.
The 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, bind water molecules by hydrogen bonds.
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 the 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, in those cases 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 living in the aquatic environment.
For aqueous solutions, 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 semipermeable septum, 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).
Water is a universal solvent adapted to any kind of life. It dissolves almost any substance, in particular ionic and polar compounds. The unique properties of the impact are characterized by a high dielectric constant. In nature, water contains a lot of substances and compounds that got into it in 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 a process by which water is chemically bonded with an added substance.
The dissolution of substances is characterized by:
- hydration that occurred;
- a change in the color of the solution;
- thermal effects (under certain conditions) and other factors.
A change in the color of the solution is evidence that mixing has occurred. For example, an admixture of copper sulfate (which is initially white) gives the water an intense blue color. If the chemical properties of the bases are responsible for the color, then the release of heat occurs due to physical reasons. Thus, this is a completely physical and chemical process.
What is a solution
A solution is a homogeneous mixture of substances with a solvent. Soluble substances break down 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 doesn't matter if you add water to some substance or pour it in. Also, the process will gradually occur and without interference (stirring), in some cases a visible precipitate is formed. In other cases, the solution is colored in the color of the added substance, but always remains transparent to the light.
The 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 dissolve in water and which do not
Water is truly versatile and unique in its properties. Sometimes it is necessary to stir harder to achieve complete destruction of the particles, but most of the water will erode any compounds. However, there are substances that are beyond even her control.
There is a condition according to which the amount of water must be exceeded in order for the substances to disperse and not settle to the bottom. For example, table salt: when a large amount is added, it stops dissolving and forms a dense, stone-like layer.
In addition, liquid can be cleaned of some substances, 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 prone to staining water, but the particles are so small that they are simply filtered along with the solution. Bulk substances like sand or clay do not dissolve, so the water can be filtered.
Classification of ability by substance:
- Well soluble (alcohol, sugar, salt (aka sodium), most alkalis and metal nitrates).
- Slightly soluble (gypsum, berthollet's 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 own 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.
Margarita Khalisova
Summary of the lesson “Water is a solvent. Water purification "
Topic: Water is a solvent. Water purification.
purpose: to consolidate the understanding that substances in water do not disappear, but dissolve.
Tasks:
1. Identify substances that dissolve in the water and which are not dissolve in water.
2. Introduce the cleaning method water - by filtration.
3. Create conditions for identifying and testing different cleaning methods water.
4. To consolidate knowledge of the rules of safe behavior when working with various substances.
5. Develop logical thinking by modeling problem situations and their solutions.
6. To cultivate accuracy and safe behavior when working with various substances.
7. Cultivate interest in cognitive activity, experimentation.
Educational areas:
Cognitive development
Social and communicative development
Physical development
Vocabulary work:
enrichment: filter, filtering
revitalization: funnel
Preliminary work: conversations about water, its role in human life; monitored water in kindergarten, at home; experiments with water; considered illustrations on the topic « Water» ; familiarized themselves with safety rules during research and experimentation; making riddles about water; reading fiction, ecological fairy tales; games about water.
Demonstration and visual material: doll in blue suit "Drop".
Handout: glasses are empty, with water; solvents: sugar, salt, flour, sand, food coloring, vegetable oil; plastic spoons, funnels, gauze napkins, cotton pads, oilcloth aprons, mugs with tea, lemon, jam, disposable plates, oilcloth on tables.
GCD move
Educator: - Guys, before starting a conversation with you, I want to make you riddle:
Lives in the seas and rivers
But it often flies across the sky.
And how bored she is with flying
Falls to the ground again. (water)
Guess what the conversation will be about? That's right, about the water. We already know that water is liquid.
Let's remember what properties water we have established with the help of experiments on others occupations... List.
Children:
1. Have no smell of water.
2. No taste.
3. It is transparent.
4. Colorless.
5. Water takes the form of the vessel into which it is poured.
6. Has weight.
Educator: - Correctly. Do you want to experiment with water again. To do this, we need to briefly turn into scientists and look into our laboratory. experimentation:
Turn right, left,
Find yourself in the laboratory.
(children go to the mini-laboratory).
Educator: - Guys, look, who is our guest again? And what's new in the laboratory?
Children: - "Drop", grandfather's granddaughter Knowing and beautiful box.
Want to know what's in this box? Guess riddles:
1. Separately - I'm not so tasty
But in food - everyone needs (salt)
2. I am white as snow,
In honor of all.
I got into my mouth -
There he disappeared. (sugar)
3. Cheesecakes are baked from me,
And pancakes and pancakes.
If you are making dough,
Must put me down (flour)
4. Yellow, not the sun,
It flows, not water,
Foams in the pan
Splashes and hisses (butter)
Food coloring - used in cooking for decorating cakes, dyeing eggs.
Sand - for construction, play with it in the sandbox.
Children examine test tubes with substances.
Educator: - All these substances brought "Drop" so that we can help her figure out what will happen to water when interacting with them.
Educator: - What do we need in order to start our work with water?
Children: - Aprons.
(children put on oilcloth aprons and come up to the table, where there are glasses of clean water on a tray).
Educator: - Let's remember the rules before we start working with these substances:
Children:
1. You cannot taste substances - there is a possibility of poisoning.
2. It is necessary to sniff carefully, as the substances can be very corrosive and can burn the respiratory tract.
Educator: - Danil will show you how to do it correctly (directing the smell from the glass with your palm).
I. Research job:
Educator: - Guys, what do you think will change if dissolve these substances in water?
I listen to the intended result of children before mixing substances with water.
Educator: - Let's check.
I suggest that the children take each glass of water.
Educator: - Look and determine which one is there water?
Children: - The water is clear, colorless, odorless, cold.
Educator: - Take a test tube with the substance you have chosen and dissolve in a glass of waterstirring with a spoon.
Considering. I listen to the children's answers. Did they guess correctly.
Educator: - What happened to sugar, salt?
Salt and sugar fast dissolve in water, the water remains clear, colorless.
Flour too dissolve in waterbut the water becomes cloudy.
But after the water will stand a little, flour settles to the bottom, but solution continues to remain cloudy.
Water with sand became dirty, muddy, if you do not interfere anymore, then the sand sank to the bottom of the glass, you can see it, that is, it does not dissolved.
Food powder solvent quickly changed color water, so dissolves well.
Oil not dissolves in water: it is either spreads on its surface as a thin film, or floats in water in the form of yellow droplets.
Water is a solvent! But not all substances dissolve in it.
Educator: - Guys, we worked with you and "Drop" invites us to rest.
(Children sit at another table and play.
A game: “Guess the drink tastes (tea)».
Tea drinking with different flavors: sugar, jam, lemon.
II Experimental work.
We approach the 1st table.
Educator: - Guys, is it possible to clean the water from these substances that we dissolved? Return it to its previous state of transparency, without sediment. How to do it?
I suggest taking your glasses with solutions and go to table 2.
Educator: - You can filter it. This requires a filter. What can you make a filter from? We will do it with a gauze pad and cotton pad. I show (in the funnel I put a gauze napkin folded in several layers, a cotton pad and put it in an empty glass).
Making filters with children.
I show the method of filtering, and then the children themselves filter the water with the substance of their choice.
I remind the children not to hurry up, pour in a small stream solution into a funnel with a filter. I say proverb: "In a hurry - you will make people laugh".
Consider what happened after filtering water with different substances.
We managed to filter the oil quickly because it didn’t dissolved in water, traces of oil are clearly visible on the filter. The same happened with the sand. Substances that are well dissolved in water: sugar, salt.
Water with flour after filtration became more transparent. Most of the flour settled on the filter, only very small particles slipped through the filter and ended up in the glass, therefore water not quite transparent.
After filtering the dye, the color of the filter has changed, but is filtered solution also remained colored.
Summary of GCD:
1. What substances dissolve in water? - sugar, salt, dye, flour.
2. What substances are not dissolve in water - sand, butter.
3.What cleaning method water we met? - filtration.
4. By what means? - filter.
5. Did everyone follow the safety rules? (one example).
6. What's interesting (new) did you find out today?
Educator: - You learned today that water - solvent, checked what substances dissolve in water and how you can purify water from different substances.
"Drop" thanks you for your help and gives you an album for sketching experiments. This concludes our research, we return from the laboratory to group:
Turn right, left.
Find yourself in the group again.
Literature:
1.AI Ivanova Environmental observations and experiments in kindergarten
2.G. P. Tugusheva, A. E. Chistyakova Experimental activities of children of middle and senior preschool age of St. Petersburg: Childhood-Press 2010.
3. Cognitive research activity of senior preschoolers - Child in kindergarten №3,4,5 2003.
4. Research activity of a preschooler - D / v №7 2001.
5. Experimenting with water and air - Д / В №6 2008.
6. Experimental activities in kindergarten - Educator of preschool educational institution №9 2009.
7. Games - experimentation of a younger preschooler - Preschool pedagogy №5 2010.