The starting materials are included unchanged in the mixture. In this case, the starting substances often become unrecognizable because the mixture exhibits different physical properties compared to each isolated starting substance. When mixed, however, no new substance arises.

The specific qualities of a mixture, such as density, boiling point or color, depend on the ratio of the mixture components (mass ratio). A mixture of two metals obtained by mixing their melts is called an alloy. In another connection they talk about a conglomerate. Colloidal solutions are in the middle between homogeneous and heterogeneous mixtures. These liquids contain solid particles, each consisting of a small number of molecules. Therefore, such a mixture behaves like a solution.

If they want to separate a mixture into pure substances, then they use some physical properties. This leads to the selection of the appropriate separation method.

Homogeneous and heterogeneous mixtures

Different types of mixtures can be classified into 2 groups:

• Heterogeneous mixtures are not completely mixed, since pure substances exist in clearly demarcated phases, that is, they are multiphase materials
• Homogeneous mixtures are mixed pure substances at the molecular level, that is, they are single-phase materials.

Homogeneous mixtures are divided according to their state of aggregation into three groups:

• gas mixtures;
• solutions;
• solid solutions.

Heterogeneous mixtures of two substances can be divided according to their states of aggregation into the following groups:

A measure indicating the proportion of substances in a mixture is concentration.

Difference between pure substances and mixtures

This distinction is most simple for gases. A pure complex substance (for example, water) consists of one type of molecules, and a mixture of gases consists of several types (for example, oxygen and hydrogen molecules). A mixture of gases can be separated by physical methods (for example, diffusion), but a complex substance cannot.

With regard to liquid and solid mixtures, everything is not always obvious.

Separation of mixtures

There are various methods for separating mixtures. For gases, these methods are based on the difference in speed or mass of molecules of substances included in the mixture.

1. The main methods for isolating substances from a heterogeneous (heterogeneous) mixture:

• upholding

• filtration

• magnet action

2. The main methods of isolating substances from a homogeneous (homogeneous) mixture:

• evaporation

• crystallization

• distillation

• chromatography

see also

Notes

Wikimedia Foundation.

2010.

See what “Mixture (chemistry)” is in other dictionaries:

Mixture: A mixture (chemistry) is a product of mixing, a mechanical combination of any substances, characterized by an impurity content above a certain limit. For example: flammable mixture, helium-oxygen mixture. Random, disorderly, devoid of... ... Wikipedia Ash and slag mixture

- Ash and slag mixture – a mixture consisting of ash and slag formed at thermal power plants when coal is burned in the furnaces of boiler units. [GOST 25137 82] Ash and slag mixture - a mechanical mixture of dusty fly ash and slag... ...

- (Eschka mixture) a mixture of two parts MgO and one part Na2CO3, a reagent that absorbs sulfur and chlorine oxides well. For example, to determine the sulfur content in coal, a sample of coal is burned with an Eshka mixture. In this case, soluble sulfates are formed... ... Wikipedia Activated mixture SFB - – a mixture prepared with water with additives, passed through a rotary pulsation apparatus and subject to cavitation; allows you to obtain an economic effect by increasing the specific surface of cement and the formation of cement... ...

Encyclopedia of terms, definitions and explanations of building materials Asphalt concrete mixture - – a mixture prepared with water with additives, passed through a rotary pulsation apparatus and subject to cavitation; allows you to obtain an economic effect by increasing the specific surface of cement and the formation of cement... ...

- - a rationally selected mixture of mineral materials [crushed stone (gravel) and sand with or without mineral powder] with bitumen, taken in certain proportions and mixed in a heated state. [GOST 9128 97] Term heading: Asphalt... ... Concrete mixture of specified quality - – a mixture prepared with water with additives, passed through a rotary pulsation apparatus and subject to cavitation; allows you to obtain an economic effect by increasing the specific surface of cement and the formation of cement... ...

- is a concrete mixture, the required properties and additional characteristics of which are specified to the manufacturer, who is responsible for providing these required properties and additional characteristics. [GOST 7473 2010] Term heading:... ... Concrete mixture of a given standardized composition - – a mixture prepared with water with additives, passed through a rotary pulsation apparatus and subject to cavitation; allows you to obtain an economic effect by increasing the specific surface of cement and the formation of cement... ...

- is a concrete mixture of a given composition, the composition of which is determined by a standard or other technical document, for example, production standards. [GOST 7473 2010] Term heading: Properties of concrete Encyclopedia headings: Abrasive... ... Concrete mixture of a given composition - – a mixture prepared with water with additives, passed through a rotary pulsation apparatus and subject to cavitation; allows you to obtain an economic effect by increasing the specific surface of cement and the formation of cement... ...

- is a concrete mixture, the composition of which and the components used in preparation are specified by the manufacturer, who is responsible for ensuring this composition. [GOST 7473 2010] Term heading: Properties of concrete Encyclopedia headings: ... ...- - a refractory mixture consisting of refractory powders and refractory cement, ready for use after the introduction of liquid. [GOST R 52918 2008] Term heading: Concreting technologies Encyclopedia headings: Abrasive equipment,... ... - – a mixture prepared with water with additives, passed through a rotary pulsation apparatus and subject to cavitation; allows you to obtain an economic effect by increasing the specific surface of cement and the formation of cement... ...

Fireproof mixture- - unshaped refractory consisting of refractory powders, ready for use after the introduction of the binder. [GOST R 52918 2008] Refractory mixture - unshaped refractories consisting of refractory powders, requiring the introduction of a binder. [GOST... - – a mixture prepared with water with additives, passed through a rotary pulsation apparatus and subject to cavitation; allows you to obtain an economic effect by increasing the specific surface of cement and the formation of cement... ...

Books

• Fundamentals of general and physical chemistry. Textbook, Eremin Vadim Vladimirovich, Borshchevsky Andrey Yakovlevich. The book is created on the basis of a one-year course “General and physical chemistry” for 2nd year students of the Faculty of Physics of Moscow State University. When choosing the level of presentation, we assumed that it would be read...

§ 13. MIXTURES AND THEIR COMPOSITION

In everyday life we ​​rarely encounterpure substances. As a fewexamples of pure substances include sugar,potassium manganate (potassium permanganate), table salt (andthen, if various additives are not added to it, for examplemeasures containing iodine for disease preventionthyroid gland)(Fig. 7).Much more often than ussurround mixtures of substances that contain two or more individual compounds, called mixture components.

Fig.7. Sugar (a), potassium permanganate (b), salt (c) - examples
pure substances used in everyday life

Mixtures differ in the size of the particles of substances included in their composition. Sometimes these particles are quite large: if you mix river sand with sugar, you can easily distinguish individual crystals from each other.

Mixtures , in which particles of their constituent substances are visible to the naked eye or under a microscope are called heterogeneous , orheterogeneous . Such mixtures include, for example, washing powder, culinary mixtures for baking pancakes or cakes, and construction mixtures.
There are mixtures, during the formation of which substances are crushed into tiny particles (molecules, ions), which are not distinguishable even under a microscope. No matter how you peer into the air, you will not be able to visually distinguish the molecules of the gases that make it up. It is useless to look for “heterogeneity” in solutions of acetic acid or table salt in water. Such mixtures are called homogeneous , or homogeneous .
Homogeneous mixtures, like chemical substances, can be divided according to their state of aggregation into gaseous, liquid and solid. The most familiar natural mixtures of gases are air, the already familiar natural and associated petroleum gases.
Of course, the most common liquid mixture on Earth, or rather a solution, is the water of the seas and oceans. One liter of sea water contains on average 35 g of salts, the main part of which is sodium chloride. Unlike pure water, sea water has a bitter-salty taste and freezes not at 0 °C, but at –1.9 °C.
You come across liquid mixtures in everyday life all the time. Shampoos and drinks, potions and household chemicals are all mixtures of substances. Even
Tap water cannot be considered a pure substance: it contains dissolved salts, tiny insoluble impurities and microorganisms, which are partially removed by chlorination or ozonation. However, in this case it is recommended to boil the water. Special household filters will help make water suitable for drinking and purify it not only of solid particles, but also of some dissolved impurities. Solid mixtures are also widespread. As we have already said, rocks are a mixture of several substances. Soil, clay, sand are also mixtures. Solid artificial mixtures include glass, ceramics, and alloys. Everyone is familiar with culinary mixtures or mixtures that form washing powders.
As you know from biology, the composition of the air that we inhale and then exhale is not the same. There is less oxygen in the exhaled air, but more carbon dioxide and water vapor. But “more” and “less” are relative concepts.
The composition of mixtures can be expressed quantitatively, i.e. in numbers. The composition of a gas mixture is expressed by the volume fraction of each of its components.
Volume fraction of gas in the mixture is the ratio of the volume of a given gas to the total volume of the mixture, expressed in fractions of a unit or percentage.
ϕ(gas) = V ( gas ) X 100 (%). V ( mixtures )
The volume fraction of gas in the mixture is denoted by the letter ϕ (phi). This value shows how much of the total volume of the mixture is occupied by a particular gas. For example, you know that the volume fraction of oxygen in the air is 21%, nitrogen - 78%. The remaining 1% comes from noble gases, carbon dioxide and other air components.
Obviously, the sum of the volume fractions of all gases in the mixture is 100%.
The composition of liquid and solid mixtures is usually expressed by a value called the mass fraction of the component.
Mass fraction of the substance in the mixture is the ratio of the mass of a given substance to the total mass of the mixture, expressed in fractions of a unit or percentage.
ω(substances) = m (in-va) X 100 (%). m ( mixtures )

Almost any tablet in a home medicine cabinet is a compressed mixture of one or more medicinal substances and a filler, which can be gypsum, starch, or glucose. Construction and culinary mixtures, perfumery compositions and paints, fertilizers and plastics have a composition that can be expressed in mass fractions of the components that form them.
Substances with impurities are also mixtures. Only in such mixtures is it customary to isolate the main (main) substance, and the extraneous components are called in one word - impurities. The fewer there are, the purer the substance.

In some areas of technology, the use of insufficiently pure substances is unacceptable. In nuclear energy, increased demands are placed not only on the purity of nuclear fuel, but also on the substances from which the installations themselves are made. A computer chip cannot be made without a particularly pure silicon crystal. The light signal in the fiberglass cable will “go out” when it encounters foreign impurities.
To separate the components of a mixture or to purify the main substance from impurities, various techniques and methods are used. As a rule, substances in a mixture retain their physical properties: boiling point, melting point, solubility in various solvents. Since the properties of one substance differ
from the properties of another, it is possible to separate the mixture into individual components. The transition of substances from one state of aggregation to another is often used.
The separation of mixtures of liquid substances is based on the difference in their boiling points. This process, as you know from the example of oil refining, is called rectification, or distillation. You already know that any gases are mixed in any ratio. Is it possible to isolate individual components from a mixture of gases? The task is not easy. But scientists have proposed a very effective solution. A mixture of gases can be turned into a liquid and subjected to distillation. For example, air is liquefied by intense cooling and compression, and then the individual components are allowed to boil off one by one, since they have different boiling points. The first of
Nitrogen evaporates in liquid air; it has the lowest boiling point (–196 °C). Argon (–186 °C) can then be removed from the liquid mixture of oxygen and argon.
What remains is almost pure oxygen (its boiling point is –183 °C, Fig. 8), which is quite suitable for gas welding, chemical production, and also for medical purposes.
Distillation is used not only to separate mixtures into individual components, but also to purify substances.
Tap water is clean, transparent, odorless... But is this substance pure from the point of view of a chemist? Look into the kettle: scale and brownish deposits remain in
as a result of repeated boiling of water in it. What about limescale on taps? Both natural and tap water are a mixture, a solution of solid and gaseous substances.

Rice. 8. In liquid form
oxygen is colored light
blue

Of course, their content in water is very small, but these impurities can lead not only to scale formation, but also to more serious consequences. It is no coincidence that injection medications, reagent solutions, and electrolyte for a car battery are prepared only using purified water, called distilled water.
Where did this name come from? The thing is that distillation is also called distillation. The essence of distillation is that the mixture is heated to a boil, the resulting vapors of the pure substance are removed, cooled and converted back into liquid. But it no longer contains contaminants.
In laboratory conditions, distillation is carried out using a special installation (Fig. 9). The mixture to be separated, for example water with substances dissolved in it, is poured into a distillation flask equipped with a thermometer and heated to a boil. The flask is connected to a downward condenser - a device for condensing vapors of a boiling substance. For this purpose, cold water is supplied into the refrigerator jacket through rubber hoses. Drops of a pure substance condensed in the refrigerator fall into the receiving flask.

Rice. 9. Laboratory installation for distillation of liquids:
1 – distillation flask; 2 – thermometer; 3 – refrigerator;
4 – receiver

What should you do if you want to isolate from a solution not a liquid, but a solid dissolved in it? For this purpose, the crystallization method is used. A solid can be isolated from a solution by crystallization by evaporating the solvent. Special porcelain cups are designed for this (Fig. 10).

Rice. 10. Evaporation
solution in porcelain
cup

This method is widely used to extract salt from concentrated solutions of salt lakes.
There is wormwood and the taste of quinine all around,
And, with strong salt soda,
The plain colored by the rays
A smooth wave licks a little.
N.Ushakov
In nature, salt lakes are like giant bowls. Due to the evaporation of water on the shores of such lakes, a huge amount of salt crystallizes, which, after purification, ends up on our table (Fig. 11).

Rice. 11. Extracting salt from salt lakes
When performing crystallization, it is not necessary to evaporate the solvent. It is known that when heated, the solubility of most solids in water increases; when a solution saturated by heating is cooled, a certain amount of crystals will precipitate.
Laboratory experiments: To 5 g of orange crystals of potassium dichromate, add several crystals of potassium permanganate (potassium permanganate) as an impurity. The mixture is dissolved in 8–10 ml of boiling water. When the solution is cooled, the solubility of potassium dichromate sharply decreases, and the substance precipitates. Crystals of dichromate purified from potassium permanganate are separated and washed with several milliliters of ice water. If you dissolve the purified substance in water, then by the color of the solution you can determine that it does not contain potassium permanganate, it remains in the original solution.
To isolate insoluble substances from liquids, the method is used defending . It is based on different densities of substances. If the solid particles are large enough, they quickly settle to the bottom, and the liquid becomes transparent (Fig. 12). It can be carefully drained from the sediment. The smaller the size of the solid particles in the liquid, the longer the mixture will settle.

Rice. 12. Soil settling in water

LABORATORY EXPERIMENT: Pour a little dishwashing powder into a glass beaker and add half a glass of water. A cloudy mixture forms.
The liquid will become clear only the next day. Why does this mixture sit for so long? Mixtures of two liquids that are insoluble in each other are also separated by settling. If water gets into the car's lubrication system, the oil will have to be drained. However, after some time the mixture will separate. Water, which has a higher density, forms the bottom layer, with a layer of oil on top.A mixture of water and oil, water and vegetable oil is settled in the same way.

To separate such mixtures it is convenient to use
special laboratory glassware called a separating funnel (Fig. 13).

Rice. 13. Separating two immiscible liquids using a separating funnel
Laboratory experiments. Equal volumes of water and vegetable oil are poured into a conical flask. Vigorous shaking breaks water and oil into small droplets, forming a cloudy mixture. It is poured into a separatory funnel. After some time, the mixture separates into a heavier water layer and oil that floats to the top. By opening the separating funnel tap, the water layer is separated from the oil layer.
Particles of solid insoluble matter can be separated from a liquid by filtration. In the laboratory, special porous paper called filter paper is used for this. Solid particles do not pass through the pores of the paper and remain on the filter. The liquid with substances dissolved in it (called filtrate) freely seeps through it and becomes completely transparent.
Filtration - a very common process in everyday life, in technology, and in nature. At water treatment plants, water is filtered through a layer of clean sand, which retains silt, oil impurities, soil and clay particles. Fuel and oil in a car engine must pass through filter elements. Cell membranes, the walls of the intestines or stomach are also unique biological filters, the pores of which allow certain substances to pass through and retain others.
It is not only liquid mixtures that can be filtered. More than once you have seen people wearing gauze bandages, and you probably had to use them yourself. Several layers of gauze with cotton wool sandwiched between them purify the inhaled air from particles of dust, smog, and pathogens (Fig. 14). In industry, special devices called respirators are used to protect the respiratory system from dust. The air entering the car engine is also cleaned of dust using fabric or paper filters.

Rice. 14. Doctors and microbiologists protect the respiratory system with special bandages.

? 1. What is a mixture? What types of mixtures are distinguished based on the state of aggregation of the substances that form them, on the basis of homogeneity?
2. Is the phrase “air molecules” correct? Why? Name the constant, variable and random components of air. Make an assumption about the relative content of individual components in the air after a thunderstorm, in deep gorges and on mountain peaks, in a forested area and near a large industrial enterprise.

3. What volume of oxygen is contained in 500 m3 (n.s.) of air?
4. In the natural gas of a certain field, the volume fractions of saturated hydrocarbons are equal: methane - 85%, ethane - 10%, propane - 4% and butane - 1%. What volume of each gas can be produced from 125 liters of natural gas (n.o.)?
5. The composition of the dry cement mixture for plastering work includes 25% cement and 75% sand. How many kilograms of each component do you need to take to prepare 150 kg of such a mixture?
6. Name the methods known to you for separating mixtures. What is the basis of each of them? Suggest a method for separating the following mixtures:
a) iron and copper filings;
b) sand and sawdust;
c) gasoline and water;
d) chalk whitewash (divided into chalk and water);
e) a solution of ethyl alcohol in water.
7. During a flu epidemic, doctors recommend wearing gauze bandages. For what? How to make such a bandage? How long can it be worn? How to restore the protective properties of the bandage?
8. Prospectors separated gold sand from ordinary sand by stirring up the soil in water and draining the muddy liquid from the sediment. This is where the expression “panning for gold” comes from. What property do you think of gold sand is based on its separation from grains of waste rock?
9. Prepare messages on the topics: “Paints in the hands of the artist” and “Famous perfumers” using Internet resources.

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

Mixtures of substances can be homogeneous or heterogeneous. In a homogeneous mixture, the components cannot be detected by observation, but in a heterogeneous mixture this is possible.

Some physical properties of a homogeneous mixture differ from the properties of the components.

In a heterogeneous mixture, the properties of the components are preserved.

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

Pure substances and mixtures

We live among chemicals. We inhale air, which is a mixture of gases (nitrogen, oxygen and others), and exhale carbon dioxide. We wash ourselves with water - this is another substance, the most common on Earth. We drink milk - a mixture of water with tiny droplets of milk fat, and not only: there is also the milk protein casein, mineral salts, vitamins and even sugar, but not the one with which you drink tea, but a special milk protein - lactose. We eat apples, which consist of a whole set of chemicals - here there is sugar, malic 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 healthy substances not only apples, 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 is built of chemicals, like a house of bricks. Nitrogen, oxygen, sugar, vitamins are substances of natural origin. Glass, rubber, steel are also substances, or rather, materials (mixtures of substances). Both glass and rubber are of artificial origin; they did not exist in nature. Absolutely pure substances are not found in nature or are found very rarely.

Each substance always contains a certain amount of impurities. A substance in which there are almost no impurities is called pure. They work with such substances in a scientific laboratory or school chemistry lab. Note that absolutely pure substances do not exist.

An individual pure substance has a certain set of characteristic properties (constant physical properties). Only pure distilled water has melting point = 0 °C, boiling point = 100 °C, and has no taste. Sea water freezes at a lower temperature and boils at a higher temperature; its taste is bitter and salty. The water of the Black Sea freezes at a lower temperature and boils at a higher temperature than the water of the Baltic Sea. Why? The fact is that sea water contains other substances, for example dissolved salts, i.e. it is a mixture of various substances, the composition of which varies widely, but the properties of the mixture are not constant. The definition of the concept “mixture” was given in the 17th century. English scientist Robert Boyle: “A mixture is an integral system consisting of heterogeneous components.”

Mixtures include almost all natural substances, food products (except salt, sugar, and some others), many medicines and cosmetics, household chemicals, and building materials.

Comparative characteristics of the mixture and pure substance

Each substance contained in a mixture is called a component.

Classification of mixtures

There are homogeneous and heterogeneous mixtures.

Homogeneous mixtures (homogeneous)

Add a small portion of sugar to a glass of water and stir until all the sugar has dissolved. The liquid will taste sweet. Thus, the sugar did not disappear, but remained in the mixture. But we will not see its crystals, even when examining a drop of liquid through a powerful microscope. The prepared mixture of sugar and water is homogeneous; the smallest particles of these substances are evenly mixed.

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 (used to make jewelry), there are no red copper particles and yellow gold particles.

Many items for various purposes are made from materials that are homogeneous mixtures of substances.

Homogeneous mixtures include all mixtures of gases, including air. There are many homogeneous mixtures of liquids.

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

Let us give examples of solutions (air in a flask, table salt + water, small change: aluminum + copper or nickel + copper).

Heterogeneous mixtures (heterogeneous)

You know that chalk does not dissolve in water. If its powder is poured into a glass of water, then in the resulting mixture you can always find chalk particles that are visible to the naked eye or through a microscope.

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

Heterogeneous mixtures include most minerals, soil, building materials, living tissues, muddy water, milk and other food products, some medicines and cosmetics.

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

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

Methods for separating mixtures

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

There are many methods for separating mixtures. They are selected taking into account the type of mixture, state of aggregation and differences in the physical properties of the components.

Methods for separating mixtures

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

Let's consider ways to separate heterogeneous and homogeneous mixtures.

If you separate a mixture of alcohol and water, then the alcohol with boiling point = 78 °C will be distilled off first (collected in a receiving test tube), and water will remain in the test tube. Distillation is used to produce gasoline, kerosene, and gas oil from oil.

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

If you hang a strip of filter paper over a container of red ink, immersing only the end of the strip in it. The solution is absorbed by the paper and rises along it. But the paint rise boundary lags behind the water rise boundary. This is how two substances are separated: water and the coloring matter in the ink.

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

A pure substance has a certain constant compound or structure(salt, sugar).

A pure substance can be element or connection.

An atom is the smallest particle of an element that retains all its properties. A chemical element consists of atoms of the same type. In an element, all atoms are the same and have the same number of protons. Elements are, in a way, the “building blocks” of any substance. We can give a construction analogy:

Building materials (brick, concrete, sand...) are elements
Building structures (houses, bridges, roads...) are a substance

2. Connections of elements

A connection consists of at least two elements. The same water consists of a combination of two elements of hydrogen and one element of oxygen - H 2 O. In other words, by combining these two elements in this way, we get water and only water!

Although water is composed of the elements hydrogen and oxygen, its chemical and physical properties are different from those of pure hydrogen and oxygen.

To “split” water into hydrogen and oxygen, it is necessary to carry out a chemical reaction.

3. Mixtures

Mixtures are physical combinations of pure substances that do not have a specific or pure composition.

An example of a mixture is ordinary tea (drink), which many people prepare and drink on their own in the morning. Some people like strong tea (a large amount of tea leaves), others like sweet tea (a large amount of sugar)... As you can see, the mixture called “tea” always turns out a little different, although it consists of the same components (ingredients). However, it should be noted that each component of the mixture retains a set of its characteristics, therefore, different substances can be isolated from the mixture. For example, you can easily separate a mixture of salt and sand. To do this, just place the mixture in water, wait until the salt dissolves and filter the resulting solution. The result is clean sand.

Mixtures can be homogeneous or heterogeneous.

In a homogeneous mixture, particles of the substances that make up the mixture cannot be detected. Samples taken in different places of such a mixture will be the same (for example, sweet tea in which the poured sugar has completely dissolved).

However, if sugar is not completely dissolved in a glass of tea, then we will get a heterogeneous mixture. Indeed, if you try this tea, it will not be as sweet from the surface as from the bottom, because... The sugar concentration will vary.