Milk is a homogeneous mixture. Mixtures and their composition

I. New material

In preparing the lesson, materials of the author were used: N.K.Cheremisina,

chemistry teachers high school № 43

(Kaliningrad),

We live among chemical substances. We inhale air, and this is a mixture of gases ( nitrogen, oxygen and others), exhale carbon dioxide. We wash ourselves water- This is another substance, the most common on Earth. We drink milk- mixture water with tiny drops of milk fat, and not only: there is still milk protein casein, mineral salt, vitamins and even sugar, but not the one with which they drink tea, but a special, milky one - lactose. We eat apples, which consist of a whole range of chemicals - here and sugar, and Apple acid, and vitamins... When chewed apple pieces enter the stomach, human digestive juices begin to act on them, which help to absorb all the tasty and useful material not only an apple, but also any other food. We not only live among chemicals, but we ourselves are made of them. Every person - his skin, muscles, blood, teeth, bones, hair are built of chemicals, like a house of bricks. Nitrogen, oxygen, sugar, vitamins are substances of natural, natural origin. Glass, rubber, steel is also a substance, more precisely, materials(mixtures of substances). Both glass and rubber are of artificial origin; they did not exist in nature. Completely pure substances are not found in nature or are very rare.

What is the difference between pure substances and mixtures of substances?

An individual pure substance has a certain set of characteristic properties (constant physical properties). Only pure distilled water has tmelt = 0 °С, tboil = 100 °С, and has no taste. Sea water freezes at a lower temperature, and boils at a higher temperature, its taste is bitter-salty. The water of the Black Sea freezes at a lower temperature, and boils at a higher temperature. high temperature than the water of the Baltic Sea. Why? The point is that in sea ​​water contains other substances, such as dissolved salts, i.e. it is a mixture of various substances, the composition of which varies over a wide range, but the properties of the mixture are not constant. The concept of "mixture" was defined in the 17th century. English scientist Robert Boyle : "A mixture is an integral system consisting of heterogeneous components."

Comparative characteristics of a mixture and a pure substance

Mixtures differ from each other in appearance.

The classification of mixtures is shown in the table:

Here are examples of suspensions (river sand + water), emulsions (vegetable oil + water) and solutions (air in a flask, salt + water, small change: aluminum + copper or nickel + copper).

In suspensions, solid particles are visible, in emulsions - liquid droplets, such mixtures are called heterogeneous (heterogeneous), and in solutions the components are not distinguishable, they are homogeneous (homogeneous) mixtures.

Methods for separating mixtures

In nature, substances exist in the form of mixtures. For laboratory research, industrial production, for the needs of pharmacology and medicine, pure substances are needed.

Used to purify substances various ways separation of mixtures

These methods are based on differences in the physical properties of the components of the mixture.

Consider waysseparationheterogeneous and homogeneous mixtures .

A special method of separating components, based on their different absorption by a certain substance, is chromatography.

At home, you can do the following experiment. Hang a strip of filter paper over the bottle of red ink, dipping only the end of the strip into it. The solution is absorbed by the paper and rises along it. But the border of the rise of the paint lags behind the border of the rise of the water. This is how the separation of two substances occurs: water and the coloring matter in the ink.

With the help of chromatography, the Russian botanist M. S. Tsvet was the first to isolate chlorophyll from the green parts of plants. In industry and laboratories, instead of filter paper for chromatography, starch, coal, limestone, and aluminum oxide are used. Are substances always required with the same degree of purification?

For different purposes, substances with different degrees of purification are needed. Cooking water is sufficiently settled to remove impurities and chlorine used to disinfect it. Drinking water must first be boiled. And in chemical laboratories, for the preparation of solutions and experiments, in medicine, distilled water is needed, as purified as possible from the substances dissolved in it. Highly pure substances, the content of impurities in which does not exceed one millionth of a percent, are used in electronics, semiconductor, nuclear technology and other precision industries.

Read L. Martynov's poem "Distilled Water":

Water
Favored
pour!
She is
shone
So pure
Whatever to drink
Don't wash.
And it was no accident.
She missed
Willows, tala
And the bitterness of flowering vines,
She missed seaweed
And fish oily from dragonflies.
She missed being wavy
She missed flowing everywhere.
She didn't have enough life.
Clean -
Distilled water!

Application of distilled water

II. Tasks for fixing

1) Work with machines #1-4(necessarydownload the simulator, it will open in the Internet Explorer browser)

In chemistry, there are concepts of pure substances and mixtures. Pure molecules contain molecules of only one substance. In nature, mixtures consisting of different substances predominate.

Concepts

All substances can be divided into two categories - pure and mixed. Pure substances include elements and compounds consisting of identical atoms, molecules or ions. These are substances with a constant composition that retain constant properties.
Examples of pure substances are:

• metals and inert gases, consisting of atoms;
• water, consisting of water molecules;
• table salt, consisting of sodium cations and chloride anions.

Rice. 1. Pure substances.

If sugar is mixed into water, it will cease to be a pure substance, a mixture is formed. Mixtures consist of several pure substances of different structure, which are called components. Mixtures can have any state of aggregation. For example, air is a mixture of various gases (oxygen, hydrogen, nitrogen), gasoline is a mixture organic matter, brass - a mixture of zinc and copper.

Rice. 2. Mixes.

Each substance retains its properties, therefore water with salt is salty, and an alloy with iron is attracted by a magnet. However, the properties of the mixture itself may vary according to the quantity and qualitative composition components. For example, distilled water that has undergone maximum purification, depending on the added substances, may acquire a sweet, sour, salty or sour-salty taste. Moreover, the higher the concentration of a certain substance, the more pronounced a certain taste.

The structure of the mixture can be homogeneous or combine substances in different states of aggregation. In accordance with this, there are:

• homogeneous or homogeneous - particles cannot be detected without chemical analysis, their index is the same anywhere in the sample (metal alloy);
• heterogeneous or heterogeneous - particles are easy to detect, their frequency is not uniform in different places of the mixture (water with sand).

Heterogeneous mixtures include:

• suspensions - mixtures of solid and liquid substances (coal and water);
• emulsions - mixtures of liquids of different density (oil and water).

If one component is inferior in mass ten times to another component, then it is called an impurity.

Cleaning methods

Absolutely pure substances do not exist. Pure substances are substances containing a small amount of impurities that do not affect the physical and chemical properties substances. In order to purify the substance as much as possible, we use ways to separate mixtures:

• settling - settling of heavy substances in liquids;
• filtration - separation of particles from liquid using filters;
• evaporation - heating the solution until moisture evaporates;
• application of a magnet - selection by means of magnetization;
• distillation - separation of substances with different boiling points;
• adsorption - the accumulation of one substance on the surface of another.

Metals from non-metals can be separated by flotation. This is a process based on the wettability of substances. In this way, iron is separated from sulfur: iron gets wet and settles to the bottom, and sulfur does not get wet and remains on the surface of the water.

Rice. 3. Flotation.

What have we learned?

From the 8th grade chemistry lesson, we learned about the concepts of mixtures and pure substances. Elements and compounds consisting of homogeneous molecules, atoms or ions, as well as having constant properties, are called pure. Mixtures include several pure substances of different concentration and structure. Compounds can mix completely, forming homogeneous substances, or combine inhomogeneously. Various methods are used to separate mixtures.

>> Pure substances and mixtures. Settling. Separation of a mixture of three solids

Pure substances and mixtures

The paragraph will help you:

> realize that absolutely pure substances do not exist;
> distinguish between homogeneous and inhomogeneous mixtures of substances;
> find out in which mixtures physical properties components are preserved, and in which - not;
> select separation method mixtures of substances depending on its type.

Pure substances and mixtures.

Each substance always contains a certain amount of impurities. A substance that contains almost no impurities is called pure. With these substances work in the scientific laboratory, school chemistry room. Note that absolutely pure substances do not exist.

Each substance contained in a mixture is called a component.

Mixtures in which components cannot be detected by observation are called homogeneous.

Most metal alloys are also homogeneous mixtures. For example, in an alloy of gold and copper (it is used to make jewelry) are missing red copper particles and yellow gold particles.

From materials that are homogeneous mixtures of substances, many items for various purposes are made (Fig. 27).

All mixtures belong to homogeneous mixtures. gases, including air. There are many homogeneous mixtures of liquids.

Rice. 27. Items made from homogeneous mixtures

Such a mixture is formed by mixing, for example, alcohol and water.

Give an example of a homogeneous mixture.

Homogeneous mixtures are also called solutions, even if they are solid or gaseous.

For some physical properties homogeneous mixtures differ from their components. Thus, an alloy of tin and lead, used for soldering, melts at a lower temperature than pure metals. Water boils at 100°C and water solution salt - at a higher temperature. If water is cooled to 0°C, it will begin to turn into ice. A salt solution under these conditions remains a liquid (it freezes at temperatures below 0 ° C). This can be seen in winter, when roads and sidewalks covered with ice are sprinkled with a mixture of salt and sand. Ice melts under the influence of salt; an aqueous solution of salt is formed, which does not freeze in mild frost. And sand is needed so that the road is not slippery.

Rice. 28. Heterogeneous mixture of chalk and water

You know that chalk does not dissolve in water. If its powder is poured into a glass of water, then chalk particles can always be found in the resulting mixture, which are visible to the naked eye or through a microscope (Fig. 28).

Mixtures in which components can be detected by observation are called heterogeneous.

Heterogeneous mixtures (Fig. 29) include most minerals, soil, Construction Materials, living tissues, cloudy water, milk and other foodstuffs, some medicines and cosmetics.

Give an example of an inhomogeneous mixture.

In a heterogeneous mixture, the physical properties of the components are preserved. So, iron filings, mixed with copper or aluminum, do not lose their ability to be attracted to a magnet.

Rice. 29. Heterogeneous mixtures:
a - a mixture of water and sulfur;
b - a mixture of vegetable oil and water;
c - a mixture of air and water

Water mixed with sand, chalk or clay freezes at 0°C and boils at 100°C.

Some types of heterogeneous mixtures have special names: foam (for example, foam, soap suds), suspension (a mixture of water with a small amount of flour), emulsion (milk, well-shaken vegetable oil with water), aerosol (smoke, fog).

What are the ingredients in each named mixture?

The material presented above is summarized in Scheme 3.

Scheme 3. Substances and mixtures

It often becomes necessary to separate a mixture in order to obtain its components or to purify a substance from impurities.

There are many methods for separating mixtures. They are chosen taking into account the type of mixture, state of aggregation and differences in the physical properties of the components (Scheme 4). Some methods you know from the course of natural history.

Scheme 4. Methods for separating mixtures

Explain what properties of the components make it possible to separate each heterogeneous mixture indicated in the diagram.

Rice. 30. Worker in a respirator

Consider how some methods separation of mixtures.

The filtering process underlies the operation of a respirator, a device that protects the lungs of a person working in a heavily dusty environment. The respirator has filters that prevent dust from entering the lungs (Fig. 30). The simplest respirator is a bandage made of several layers of gauze. A filter that extracts dust from the air is also in the vacuum cleaner.

With the help of a magnet in industry enrich iron ore- magnetite.

Due to the ability to be attracted to a magnet, the ore is separated from sand, clay, earth, etc. In this way, iron is extracted from industrial and domestic waste.

An important method for separating homogeneous mixtures of liquids is distillation, or distillation. This method allows you to clear natural water from impurities. The resulting pure (distilled) water is used in research laboratories, in the production of substances for modern technology, in medicine for the preparation of medicines.

1 The term comes from the Latin word distillatio - dripping.

In industry, the distillation of oil (a mixture of many substances, mainly liquids) produces gasoline, kerosene, and diesel fuel.

In the laboratory, distillation is carried out on special installation(Fig. 31). When a mixture of liquids is heated, the substance with the lowest boiling point boils first. Its vapor leaves the vessel, cools, condenses1, and the resulting liquid flows into the receiver. When this substance is no longer in the mixture, the temperature will begin to rise, and over time, another liquid component will boil. Non-volatile liquids remain in the vessel.

Rice. 31.Laboratory installation for distillation:

a - ordinary;
1 - a mixture of liquids with different temperatures boiling;
2 - thermometer;
3 - water cooler;
4 - receiver
6 - simplified

The separation of various mixtures also occurs in nature. Dust particles settle from the air, and during rain and snow - water droplets, snowflakes. As a result of settling, cloudy water becomes transparent. Water is also purified from insoluble substances when passing through sand. After the evaporation of water, salts remain on the banks of the estuaries, which were dissolved in it. Dissolved gases are released from the water flowing from the well.

1 The term comes from the Latin word condensatio - thickening, compaction.

conclusions

Every substance contains impurities. A substance is considered pure if it contains almost no impurities.

Mixtures of substances are either homogeneous or heterogeneous. In a homogeneous mixture, the components cannot be detected by observation, but in an inhomogeneous mixture it is possible.

Some physical properties of a homogeneous mixture differ from those of the components. In a heterogeneous mixture, the properties of the components are preserved.

Inhomogeneous mixtures of substances are separated by settling, filtering, sometimes by the action of a magnet, and homogeneous mixtures are separated by evaporation and distillation (distillation).

?
29. What types of mixtures are there and how do they differ?

30. Write down the given words and phrases in the appropriate columns of the table below: aluminum, ash, newsprint, mercury, air, iodine tincture, granite, ice from clean water, carbon dioxide, reinforced concrete.

31. Name a few foods that are solutions.

32. What popular drink, depending on the method of preparation, is a homogeneous or heterogeneous mixture?

33. Can an aqueous solution of table salt be turned into a heterogeneous mixture? If possible, how to do it?

34. What mixtures can be separated by filtration: a) a mixture of sand and clay; b) a mixture of alcohol and copper filings; c) a mixture of water and gasoline; d) a mixture of water with pieces of plastic? Name the substances that will remain on the filter.

35. How would you separate the mixture of: a) table salt and chalk; b) alcohol and water? What differences in the properties of substances make it possible to use the method you have chosen?

36. Consider an experiment to separate a mixture of table salt, sand, iron and sawdust. Make a plan for it, briefly describe each stage of the experiment and talk about the expected results.

Experimenting at home

settling

Pour water into two glasses. Pour 1/2 teaspoon of sand into one glass, and the same amount of starch into another. Stir both mixtures at the same time. Do particles of matter settle in water at the same rate? If not, which particles settle faster and why?

Write down your observations in a notebook.

Separation of a mixture of three solids

Mix small amounts of crushed styrofoam, sand and table salt.

What methods can be used to separate this mixture?

Divide mixture 1 . If heating is necessary, use it very carefully.

Describe each step of the experiment in your notebook.

Popel P. P., Kriklya L. S., Chemistry: Pdruch. for 7 cells. zahalnosvit. navch. zakl. - K .: Exhibition Center "Academy", 2008. - 136 p.: il.

Chemistry is the study of substances and their properties. When they are mixed, mixtures arise that acquire new valuable qualities.

What is a mixture

A mixture is a collection of individual substances. They are not only made by scientists in laboratories under certain conditions. Every day we start with fragrant tea or coffee, to which we add sugar. Or we cook tasty soup, which must be salted. These are the real mixtures. We just don't think about it at all.

If it is impossible to distinguish particles of substances with the naked eye, then you have homogeneous mixtures (homogeneous). They can be obtained by dissolving the same sugar in tea or coffee.

But if you add sand to sugar, their particles can be distinguished without difficulty. Such a mixture is considered heterogeneous or heterogeneous.

In the manufacture of mixtures of this type, it is possible to use substances that are in different states of aggregation: solid or liquid. Ground pepper mixture different kind or other seasonings are most often heterogeneous dry formulations.

If any liquid is used in the process of preparing a heterogeneous product, then the resulting mass is called a suspension. And there are several types of them. When liquids are mixed with solids, suspensions are formed. Their example is a mixture of water with sand or clay. When a builder makes cement, a cook mixes flour with water, a child brushes his teeth with toothpaste, they all use slurries.

Another kind of heterogeneous mixtures can be obtained by mixing two liquids. Naturally, if their particles are distinguishable. Drop vegetable oil into water - and get an emulsion.

Related videos

Homogeneous mixtures

The best known of this group of substances is air. Every student knows that it contains a number of gases: nitrogen, oxygen, carbon dioxide, water vapor and impurities. Can they be seen and seen with the naked eye? Of course not.

Thus, both air and sweet water are homogeneous mixtures. They can be in different aggregate states. But most often liquid homogeneous mixtures are used. They consist of a solvent and a solute. Moreover, the first component is either liquid or taken in a larger volume.

Substances cannot dissolve in infinite quantities. For example, only two kilograms of sugar can be added to a liter of water. Further, this process simply will not occur. This solution will become saturated.

An interesting phenomenon is represented by solid homogeneous mixtures. So, hydrogen is easily distributed in various metals. The intensity of the dissolution process depends on many factors. It increases with an increase in the temperature of the liquid and air, with the grinding of substances and as a result of their mixing.

Surprising is the fact that absolutely insoluble substances do not exist in nature. Even silver ions are distributed between water molecules, forming a homogeneous mixture. Such solutions are found wide application in a person's life and life. For example, everyone's favorite and healthy milk is a homogeneous mixture.

Methods for separating mixtures

Sometimes it becomes necessary not only to obtain homogeneous solutions, but also to separate homogeneous mixtures. Suppose the house has only salty water, but you need to get its crystals separately. To do this, a similar mass is evaporated. Homogeneous mixtures, examples of which were given above, are most often separated in this way.

Distillation is based on differences in boiling point. Everyone knows that water begins to evaporate at 100 degrees Celsius, and ethanol- at 78. The mixture of these liquids is heated. First, the alcohol vapor evaporates. They are condensed, that is, they are transferred to a liquid state, in contact with any chilled surface.

Using a magnet, mixtures containing metals are separated. For example, iron and wood chips. Vegetable oil and water separately can be obtained by settling.

Heterogeneous and homogeneous mixtures, examples of which are illustrated in the article, have an important economic importance. Minerals, air, The groundwater, seas, food products, building materials, drinks, pastes - all this is a combination of individual substances, without which life would be simply impossible.