In our article we will consider what pure substances and mixtures are, methods of separation of mixtures. In everyday life, each of us uses them. Are pure substances found in nature at all? And how to distinguish them from mixtures?
Pure substances and mixtures: methods for the separation of mixtures
Pure substances are those that contain particles of only a certain type. Scientists believe that in nature they practically do not exist, since all of them, although in negligible proportions, contain impurities. Absolutely all substances are also soluble in water. Even if you immerse in this liquid, for example, a silver ring, 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. It is possible to divide a pure substance into separate components only by means of a chemical reaction. For example, only distilled water has a boiling and freezing point typical of this substance, and lacks taste and smell. But its oxygen and hydrogen can be decomposed only by electrolysis.
And how do they differ from pure substances in their totality? Chemistry will help us answer this question. The separation methods of the mixtures are physical, since they do not lead to a change in the chemical composition of the substances. Unlike pure substances, mixtures have a variable composition and properties, and they can be separated by physical methods.
What is a mixture?
A mixture is a combination of individual substances. Her example is seawater. Unlike disciplined, it has a bitter or salty taste, boils at a higher, and freezes at a lower temperature. Methods for separating mixtures of substances are physical. So, from salt water, you can get pure salt by evaporation and subsequent crystallization.
Types of mixtures
If sugar is added to the 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. Their examples are also air, gasoline, broth, perfume, sweet and salty water, an alloy of copper and aluminum. As you can see, homogeneous mixtures can be in different aggregate states, but liquids are most often found. They are also called solutions.
In heterogeneous or heterogeneous mixtures, particles of individual substances can be distinguished. Iron and wood filings, sand and salt are their typical examples. Inhomogeneous mixtures are also called suspensions. Among them, suspensions and emulsions are distinguished. The first includes liquid and 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 polystyrene, and aerosols include fog, smoke, deodorants, air fresheners, antistatic agents.
Methods for the separation of mixtures
Of course, many mixtures have more valuable properties than individual individual substances that make up their composition. But even in everyday life, situations arise when they need to be divided. And in industry, whole production is based on this process. For example, petroleum, gas oil, kerosene, fuel oil, diesel and engine oil, rocket fuel, acetylene and benzene are obtained from oil as a result of its processing. Agree, it is more profitable to use these products than thoughtlessly burn oil.
Now let's see if there is such a thing as chemical methods of separation of mixtures. Suppose we need to obtain pure substances from an aqueous solution of salt. To do this, the mixture must be heated. As a result, water will turn into steam, and the salt will crystallize. But at the same time, some substances will not be transformed into others. This means that the basis of this process are physical phenomena.
Methods for the separation of mixtures depend on the state of aggregation, solubility, difference in boiling point, density and composition of its components. We will consider each of them in more detail with specific examples.
Filtration
This separation method is suitable for mixtures which include a liquid and a solid insoluble in it. For example, water and river sand. This mixture must be passed through the filter. As a result, clean water will pass freely through it, and the sand will remain.
Upholding
Some methods of separating mixtures are based on the action of gravity. Thus, suspensions and emulsions can be decomposed into pure substances . If vegetable oil has got into the water, such a mixture must first be shaken. Then leave her for a while. As a result, water will be at the bottom of the vessel, and oil in the form of a film will cover it.
In laboratory conditions, a separatory funnel is used for sedimentation . As a result of her work, a denser liquid merges into the vessel, and the light remains.
Settling is characterized by a low rate of the process. It takes a certain amount of time for a precipitate to form. In industrial conditions, this method is carried out in special designs called settlers.
Magnet action
If the mixture contains metal, then it can be separated using a magnet. For example, separate iron and wood filings. But do all metals have such properties? Not at all. For this method, only mixtures containing ferromagnets are suitable. In addition to iron, these include nickel, cobalt, gadolinium, terbium, dysprosium, holmium, erbium.
Distillation
This name is translated from Latin means "dripping." Distillation presents methods for separating mixtures based on differences in the 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, alcohol vapors condense, turning into a liquid state.
In industry, oil processing products, aromatic substances, and pure metals are obtained in this way.
Evaporation and Crystallization
These separation methods of mixtures are suitable for liquid solutions. The substances that make up their composition differ in boiling point. Thus, salt or sugar crystals can be obtained from the water in which they are dissolved. For 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 vapor on a colder surface.
Methods for separating gas mixtures
Gaseous mixtures are separated by laboratory and industrial methods, since this process requires special equipment. Raw materials of natural origin are air, coke oven, generator, associated and natural gas, which is a combination of hydrocarbons.
The physical methods for separating mixtures in a gaseous state are as follows:
- Condensation is a process of gradual cooling of a mixture, during which condensation of its components occurs. In this case, first of all, high-boiling substances that 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 portion 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. For the direct and reverse process, various conditions are necessary. In the first case, this is a combination of high pressure and low temperature. This process is called sorption. In the opposite case, the opposite conditions are used: low pressure at high temperature.
- Membrane separation is a method in which the property of semipermeable partitions is used to selectively pass molecules of various substances.
- Reflux is the process of condensation of high-boiling parts of mixtures as a result of their cooling. In this case, the temperature of the transition to the liquid state of the individual components should differ to a large extent.
Chromatography
The name of this method can be translated as "writing in color." Imagine ink being added to water. If you lower the end of the filter paper into such a mixture, it will begin to absorb. In this case, water will be absorbed faster than ink, which is associated with varying degrees of sorption of these substances. Chromatography is not only a way of separating mixtures, but also a method of studying such properties of substances as diffusion and solubility.
So, we got acquainted with such concepts as "pure substances" and "mixtures". The former are elements or compounds consisting only of particles of a certain kind. Their examples are salt, sugar, distilled water. Mixtures are a combination of individual substances. A number of methods are used to separate them. The method of their separation depends on the physical properties of its components. The main ones are sedimentation, evaporation, crystallization, filtration, distillation, magnet action and chromatography.