In our article we will consider what pure substances and mixtures are, methods for separating mixtures. Each of us uses them in everyday life. Do pure substances occur in nature at all? And how to distinguish them from mixtures?
Pure substances and mixtures: ways to separate mixtures
Pure substances are substances that contain particles of only a certain type. Scientists believe that they practically do not exist in nature, since all of them, albeit in negligible proportions, contain impurities. Absolutely all substances are also soluble in water. Even if, for example, a silver ring is immersed in this liquid, the ions of this metal will go into solution.
A sign of pure substances is the constancy of composition and physical properties. In the process of their formation, a change in the amount of energy occurs. Moreover, it can both increase and decrease. A pure substance can be separated into its individual components only by a chemical reaction. For example, only distilled water has a typical boiling and freezing point for this substance,lack of taste and smell. And its oxygen and hydrogen can be decomposed only by electrolysis.
And how do their aggregates differ from pure substances? Chemistry will help us answer this question. Methods for separating mixtures are physical, since they do not lead to a change in the chemical composition of substances. Unlike pure substances, mixtures have variable composition and properties, and they can be separated by physical methods.
What is a mixture
A mixture is a collection of individual substances. An example is sea water. Unlike distilled, it has a bitter or s alty taste, boils at a higher temperature, and freezes at a lower temperature. Methods for separating mixtures of substances are physical. So, pure s alt can be obtained from sea water by evaporation and subsequent crystallization.
Types of mixtures
If you add sugar to water, after a while its particles will dissolve and become invisible. As a result, they cannot be distinguished with the naked eye. Such mixtures are called homogeneous or homogeneous. Air, gasoline, broth, perfume, sweet and s alt water, and an alloy of copper and aluminum are also examples of these. As you can see, homogeneous mixtures can be in different states of aggregation, but liquids are most common. They are also called solutions.
In heterogeneous or heterogeneous mixtures, particles of individual substances can be distinguished. Iron and wood filings, sand and table s alt are typical examples. Heterogeneous mixtures are also called suspensions. Among them, suspensions and emulsions are distinguished. The former consists of a liquid and a solid. So, an emulsion is a mixture of water and sand. An emulsion is a combination of two liquids with different densities.
There are heterogeneous mixtures with special names. So, an example of foam is foam, and aerosols include fog, smoke, deodorants, air fresheners, antistatic agents.
Methods for separating mixtures
Of course, many mixtures have more valuable properties than individual individual substances that make up them. But even in everyday life there are situations when they need to be separated. And in industry, entire industries are based on this process. For example, from oil as a result of its processing, gasoline, gas oil, kerosene, fuel oil, solar oil and machine oil, rocket fuel, acetylene and benzene are obtained. Agree, it is more profitable to use these products than mindlessly burning oil.
Now let's see if there is such a thing as chemical methods for separating mixtures. Suppose we need to obtain pure substances from an aqueous solution of s alt. To do this, the mixture must be heated. As a result, the water will turn into steam, and the s alt will crystallize. But at the same time, there will be no transformation of one substance into another. This means that the basis of this process are physical phenomena.
Methods for separating mixtures depend on the state of aggregation, the ability to dissolve, the difference in boiling point, density and composition of its components. Let's consider each of them in more detail on specificexamples.
Filtering
This separation method is suitable for mixtures containing a liquid and an insoluble solid. For example, water and river sand. This mixture must be passed through a filter. As a result, clean water will freely pass through it, and the sand will remain.
Settling
Some methods of separation of mixtures are based on the action of gravity. Thus suspensions and emulsions can be decomposed into pure substances. If vegetable oil gets into the water, the mixture must first be shaken. Then leave it for a while. As a result, the water will be at the bottom of the vessel, and the oil will cover it in the form of a film.
In laboratory conditions, a separating funnel is used for settling. As a result of its work, the denser liquid is drained into the vessel, while the light one remains.
Settling is characterized by a low speed of the process. It takes a certain amount of time for the precipitate to form. In industrial conditions, this method is carried out in special structures called sedimentation tanks.
Action with a magnet
If the mixture contains metal, it can be separated using a magnet. For example, separate iron and wood filings. But do all metals have these properties? Not at all. For this method, only mixtures containing ferromagnets are suitable. In addition to iron, these include nickel, cob alt, gadolinium, terbium, dysprosium, holmium, erbium.
Distillation
This is the title intranslated from Latin means "draining drops." Distillation is a method of separating mixtures based on the difference in boiling points of substances. Thus, even at home, alcohol and water can be separated. The first substance begins to evaporate already at a temperature of 78 degrees Celsius. Touching the cold surface, the alcohol vapor condenses, turning into a liquid state.
In industry, oil products, aromatic substances, pure metals are obtained in this way.
Evaporation and crystallization
These separation methods are suitable for liquid solutions. The substances that make up their composition differ in their boiling point. Thus, it is possible to obtain crystals of s alt or sugar from the water in which they are dissolved. To do this, the solutions are heated and evaporated to a saturated state. In this case, the crystals are deposited. If it is necessary to obtain pure water, then the solution is brought to a boil, followed by condensation of the vapors on a colder surface.
Methods for separating gas mixtures
Gas mixtures are separated by laboratory and industrial methods, since this process requires special equipment. The raw material of natural origin is air, coke, generator, associated and natural gas, which is a combination of hydrocarbons.
Physical methods for separating mixtures in the gaseous state are as follows:
- Condensation is a process of gradualcooling the mixture, during which the condensation of its components occurs. In this case, first of all, high-boiling substances, which are collected in separators, pass into the liquid state. In this way, hydrogen is obtained from coke oven gas, and ammonia is also separated from the unreacted part of the mixture.
- Sorption is the absorption of some substances by others. This process has opposite components, between which equilibrium is established during the reaction. The forward and reverse processes require different conditions. In the first case, it is a combination of high pressure and low temperature. This process is called sorption. Otherwise, the opposite conditions are used: low pressure at high temperature.
- Membrane separation is a method in which the property of semi-permeable partitions is used to selectively pass molecules of various substances.
- Refluxation - the process of condensation of high-boiling parts of mixtures as a result of their cooling. In this case, the transition temperature to the liquid state of the individual components should differ significantly.
Chromatography
The name of this method can be translated as "I write with color". Imagine that ink is added to the water. If you lower the end of the filter paper into such a mixture, it will begin to be absorbed. In this case, water will be absorbed faster than ink, which is associated with a different degree of sorption of these substances. Chromatography is not only a method for separating mixtures, but also a method for studying such properties of substances as diffusion and solubility.
So we metwith concepts such as "pure substances" and "mixtures". The first are elements or compounds consisting only of particles of a certain type. Their examples are s alt, sugar, distilled water. Mixtures are a collection of individual substances. A number of methods are used to separate them. The way they are separated depends on the physical properties of its constituents. The main ones are settling, evaporation, crystallization, filtration, distillation, magnetization and chromatography.
