Homogeneous homogeneous. Pure substances and mixtures. Defending - Knowledge Hypermarket. Section and. general chemistry

Pure substance contains only one kind of particles. Examples are silver (contains only silver atoms), sulfuric acid, and carbon monoxide (IV) (contain only the molecules of the corresponding substances). All pure substances have constant physical properties, for example, melting point (T m) and boiling point (T bale).

A substance is not pure if it contains any amount of one or more other substances - impurities.

Contamination lowers the freezing point and increases the boiling point of a clean liquid. For example, if you add salt to the water, the freezing point of the solution will drop.

Mixes consist of two or more substances. Soil, sea water, air are all examples of different mixtures. Many mixtures can be divided into constituent parts - Components- based on the difference in their physical properties.

Distinguish homogeneous (homogeneous) and heterogeneous (inhomogeneous) mixtures. Feature homogeneous mixture is that no interface is observed between the components of such a mixture. In this case, the mixture is said to be single phase(phase part of the system separated from other parts by a visible interface). Within one phase, the physical properties of the components are kept constant. TO homogeneous systems include true solutions (the size of the solute particles correlates with the size of the solvent particles and is ≤10 -9 m).

Feature heterogeneous mixture is that we can observe the interface between its components. During the transition from one phase of a component to another, its properties change dramatically. Heterogeneous mixtures are otherwise called dispersed systems. Disperse systems consist of a dispersion medium (solvent, continuous phase) and a dispersed phase (solute or discontinuous phase)

TO heterogeneous mixtures include dispersed systems (the particle size of the solute is significantly greater than the size of the solvent particles and is ≥10 -9 m). Mixtures in which the particle size of a substance is 10 -7 -10 -9 m are referred to colloidal systems.

Dispersed systems include:

Suspensions, a mixture consisting of a solid and a liquid phase (designation S / L; T - dispersed phase, L - dispersion medium)

Emulsions, a mixture of 2 or more immiscible liquids (designation - Zh / Zh. Disperse phase and dispersion medium of a liquid differing in density and boiling point).

These systems will be discussed in more detail in the topic solutions and dispersed systems.

1.5. Separation methods

Traditional methods that are used in laboratory practice to separate mixtures into individual components are:

filtration,

decantation ( in chemical laboratory practice and chemical technology, mechanical separation of the solid phase of the dispersed system (suspension) from the liquid by draining the solution from the sediment),

separation with a separating funnel,

centrifugation,

evaporation,

crystallization,

distillation (including fractional distillation),

chromatography,

sublimation and others.

Filtration. Filtration is used to separate liquids from small solid particles suspended in it. (fig. 37), i.e. filtering liquid through finely porous materials - filters that allow liquid to pass through and retain solid particles on their surface. The liquid that has passed through the filter and is freed from the solid impurities contained in it is called filtrate.

In laboratory practice, they are often used smooth and folded paper filters (fig. 38) made from non-glued filter paper.

For filtering hot solutions (for example, for the purpose of recrystallizing salts), use a special hot filter funnel(fig. 39) with electric or water heating).

Often used vacuum filtration... Vacuum filtration is used to accelerate filtration and more complete removal of the solid phase from the liquid. For this purpose, a vacuum filtration device is assembled. (fig. 40)... It consists of Bunsen flasks, porcelain Buchner funnel, safety flask and vacuum pump(usually water jet).

In the case of filtration of a suspension of a poorly soluble salt, the crystals of the latter can be washed with distilled water on a Buchner funnel to remove the initial solution from their surface. For this purpose use wash bottle(fig. 41).

Decantation... Liquids can be separated from insoluble solids by decantation (fig. 42)... This method can be used if the solid has a higher density than the liquid. For example, if river sand is added to a glass of water, then during settling it will settle to the bottom of the glass, because the density of the sand is greater than that of water. Then the water can be separated from the sand by simply draining. This method of settling and then draining the filtrate is called decantation.

Centrifugation. To accelerate the separation of very small particles that form stable suspensions or emulsions in the liquid, the centrifugation method is used. This method can be used to separate mixtures of liquids and solids that differ in density. The division is carried out in manual or electric centrifuges (fig. 43).

Separation of two immiscible liquids, having different densities and not forming stable emulsions, can be carried out using a separating funnel (fig. 44)... In this way, for example, a mixture of benzene and water can be separated. A layer of benzene (density  = 0.879 g / cm 3) is located above a layer of water, which has a high density ( = 1.0 g / cm 3). By opening the tap of the separating funnel, you can carefully drain the bottom layer and separate one liquid from the other.

Evaporation(fig. 45)- this method involves removing a solvent, for example water, from a solution while heating it in an evaporating porcelain cup. In this case, the evaporated liquid is removed, and the solute remains in the evaporation dish.

Crystallization Is the process of separating crystals of a solid when cooling a solution, for example, after evaporating it. It should be borne in mind that when the solution is slowly cooled, large crystals are formed. On rapid cooling (for example, when cooling with running water), small crystals are formed.

Distillation- a method of cleaning a substance based on the evaporation of a liquid upon heating, followed by condensation of the resulting vapors. Purification of water from salts dissolved in it (or other substances, for example, coloring) by distillation is called distillation, and the purified water itself is distilled.

Fractional distillation (distillation)(fig. 46) used to separate mixtures of liquids with different boiling points. Liquid with a lower boiling point boils faster and passes through earlier fractional column(or dephlegmator). When this liquid reaches the top of the fractional column, it enters fridge, is cooled by water and through allonge going to receiver(flask or test tube).

Fractional distillation can separate, for example, a mixture of ethanol and water. The boiling point of ethanol is 78 0 С, and the boiling point of water is 100 0 С. Ethanol evaporates more easily and is the first to enter the receiver through the refrigerator.

Sublimation - the method is used to purify substances that, when heated, can pass from a solid state to a gaseous state, bypassing the liquid state. Further, the vapors of the purified substance are condensed, and the impurities that are not capable of sublimation are separated.

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

The pure substance can be element or connection.

An atom is the smallest particle of an element that retains all of its properties.. Chemical element consists of atoms of the same kind. In an element, all atoms are the same and have the same number of protons. Elements are a kind of "building blocks" of any substance. You can give a construction analogy:

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

2. Connections of elements

The connection consists of at least two elements. All the same water consists of a combination of two elements hydrogen and one element oxygen - H 2 O. In other words, 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 differ from those of pure hydrogen and oxygen.

To "separate" water into hydrogen and oxygen, a chemical reaction must be performed.

3. Mixes

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

An example of a mixture is ordinary tea (drink), which many people prepare and drink on their own in the morning. Someone loves strong tea (a large amount of infusions), someone loves sweet tea (a large amount of sugar) ... As you can see, the mixture called "tea" always turns out to be 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, it is enough to place the mixture in water, wait until the salt dissolves and filter the resulting solution. As a result, we get clean sand.

Mixtures can be homogeneous or heterogeneous.

In a homogeneous mixture, it is impossible to detect particles of substances that make up the mixture. 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 does not completely dissolve in a glass of tea, then we will get a heterogeneous mixture. Indeed, if you try such tea, then from the surface it will not be as sweet as from the bottom, because the concentration of sugar will vary.

SECTION I. GENERAL CHEMISTRY

6. Mixtures of substances. Solutions

6.2. Mixtures, their types, names, composition, separation methods

Mixtures are a combination various substances, of which one can be added physical body... Each substance that is contained in the mixture is called a component. When mixed, a new substance does not arise. All substances that are part of the mixture retain their inherent properties. But the physical properties of the mixture, as a rule, differ from the physical properties of the individual components. Mixtures are homogeneous and heterogeneous.

Homogeneous (homogeneous) mixtures are mixtures in which the components are mixed on molecular level(single phase material); they cannot be detected when viewed with the naked eye and even when using powerful optical instruments. For example, aqueous solutions of sugar, table salt, alcohol, acetic acid, metal alloys, air.

Inhomogeneous (heterogeneous) mixtures form the so-called dispersed systems. They are formed by mixing two or more substances that do not dissolve in each other (do not form homogeneous systems) and do not react chemically. The components of dispersed systems are called the dispersed medium and the dispersed phase; there is a separation surface between them.

According to the particle size of the dispersed phase, the systems are divided into:

Coarsely dispersed (> 10 -5 m);

Microheterogeneous (10 -7 -10 -5 m);

Ultra-microheterogeneous (10 -9 -10 -7 m), or sols (colloidal systems) 1.

If the particles of the dispersed phase have the same size, the systems are called monodisperse; if different - polydisperse (such are practically all natural systems). Depending on the state of aggregation of the dispersion medium and the dispersed phase, such simple dispersed systems are distinguished:

* Gases form homogeneous mixtures (gaseous solutions).

** Porous bodies, according to the size of the cavities, are divided into:

Microporous (2 nm);

Lesoporous (2-50 nm);

Macroporous (> 50 nm).

The mixtures are separated using physical methods. To separate heterogeneous mixtures, sedimentation, filtration, flotation and sometimes the action of a magnet are used.

To separate homogeneous mixtures, evaporation and distillation (distillation) are used.

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1 If the particle size of the dispersed phase does not exceed the size of molecules or ions (up to 1 nm), such systems are called true solutions.

Give 5 examples of homogeneous and heterogeneous mixtures that you encounter every day. and got the best answer

Answer from Yergey Meshalkin [active]
A homogeneous mixture is a mixture where substances are in one phase, they are also called homogeneous.
An inhomogeneous mixture is a mixture where substances are in different phases. for example, solid and liquid or gaseous and liquid. another name is heterogeneous systems.
an example of homogeneous mixtures is a sulfuric acid solution - a mixture of water and acid (electrolyte in a battery), a solution of sugar in tea, broth, perfume, gasoline.
examples of heterogeneous mixtures are sand in water (aquarium), soup, earth in a pot, tea with infuser, indoor air (dust!).

Answer from Ekaterina Andreeva[newbie]
guys thanks

Answer from Karina Afanasenko[newbie]
One. : air, sweet water, salt water, alcohol + water, glass.
Not one. : oil + water, turbid water, blood (visible under a microscope), dusty air, sand.

Answer from Tim Verlov[guru]
homogeneous, though with some impurities, probably only the air that I breathe. everything else is heterogeneous, from food and water to slop and garbage 🙂

Answer from 3 answers[guru]

Hey! Here are a selection of topics to answer your question: Give 5 examples of homogeneous and heterogeneous mixtures that you encounter every day.