Everyone knows from the course of natural history what substances are called pure. We will recall the definition of this concept, as well as examples that we encounter in everyday life.
Essence of substances
Atoms and molecules, pure substances and mixtures… How are these concepts related? The elementary particles that make up matter are atoms. They are also called chemical elements. Connecting with each other, they form molecules, or substances. Let's take a look at these concepts with specific examples. Two hydrogen atoms and one oxygen atom together form a water molecule. Plants produce glucose during photosynthesis. The molecule of this substance consists of oxygen, hydrogen and carbon atoms.
What substances are called pure
If the composition of the substance includes particles of only one type, they are called pure. Water, sugar, s alt, gold - these are their examples. So about what substances are called pure (grade 5 studies this topic in the course of natural history), everyone knows firsthand.
But scientists believe that in nature suchthe concept simply does not exist. The point is that absolutely pure substances simply do not exist. All of them are soluble in water. Some - at the level of ions, others - molecules. Let's imagine the following experience. Silver jewelry was placed in a vessel with clean water. What will happen? Purely visually - nothing, because the metal cannot dissolve in water. However, silver ions are distributed between solvent molecules. The result is the same water purified with silver.
Life examples
The concepts that are discussed in our article, we encounter daily. What substances are called pure? Many start the day with a fragrant cup of coffee. To prepare it, you need to take several individual substances. This is water, ground coffee beans and sugar. Pure substances are also necessary for making soup. Here, in addition to water, you will need s alt, oil, and then it's a matter of taste.
All women love gold jewelry. At first glance, it may seem that this metal is an example of what substances are called pure. But it is not so. On each of these products there is a sample. For example, 585. This means the amount of gold contained in this alloy. The rest is impurities. It can be silver, copper, zinc, platinum, nickel. The higher the sample number, the better and more expensive the product. Why do we need these supplements at all? The fact is that products made of pure gold would be soft and fragile, and therefore short-lived.
Pure substances and mixtures: what is it
A set of individual substances is called a mixture. Its main characteristics include unstable composition, inconstancy of physical properties, lack of energy release during their formation.
Sweet and s alt water are already mixtures. Their formation is based on the ability of solid particles to dissolve. But will the composition of such mixtures change if they are frozen? Not at all. When passing from one state of aggregation to another, only the distance between the molecules changes, but not their composition.
Classification of mixtures
The degree of dissolution of pure substances in water allows us to distinguish two groups of solutions. In homogeneous, or homogeneous, individual components cannot be distinguished with the naked eye. They are also called solutions. Such mixtures can be not only liquid. For example, air is a solution of gases, and an alloy is solid metals.
In heterogeneous, or heterogeneous, mixtures, particles of individual substances can be distinguished with the naked eye. It's weigh. If they contain liquids and solids, they are called suspensions. An example of such mixtures is the combination of water with river sand, clay or soil.
Two liquids that are insoluble in each other are called an emulsion. Mix water with vegetable oil. Shake the resulting solution well. As a result, oil drops will unite on the surface of the water into a dense film.
Methods for separating mixtures
The advantage of mixtures is that they acquire new, most often useful, features compared to pure substances. But sometimes it is necessary to reverse the process. As you know, oil is an excellent fuel. But if hydrocarbons are isolated from this mixture, then each of them can be used separately. Therefore, it is possible to obtain several types of fuel, which is very advantageous. These include gasoline, kerosene, gas oil, fuel oil.
There are several ways to separate mixtures. Each of them is determined by the properties of individual substances. So, for homogeneous mixtures, evaporation and crystallization are used. But this is only possible if solids are dissolved in the liquid. If two liquids with different boiling points are mixed, they can be separated by distillation. So, alcohol boils at 78 degrees, and water at 100.
Heterogeneous mixtures can be separated by magnetic action, settling and filtering. An example of the first method is a combination of iron and wood filings. This method is based on different magnetic properties of substances. Filtration is suitable for mixtures with different solubility and particle sizes. For its implementation, a special device is used. This is the filter: cotton wool, gauze and even a strainer that we use to make tea. If the slurry components have different densities, settling can be used.
So, we remembered what substances are called pure. They consist of particles of only a certain kind. Their combination is called a mixture. Depending on the physicalproperties of constituent substances, it can be homogeneous or heterogeneous.
