Everyone knows from a course in natural science what substances are called pure. We will recall the definition of this concept, as well as examples that we encounter in everyday life.
Substance
Atoms and molecules, pure substances and mixtures ... How are these concepts related? The elementary particles that make up the substance are atoms. They are also called chemical elements. Connecting with each other, they form molecules, or substances. We will analyze these concepts using specific examples. Two hydrogen atoms and one oxygen combine to form a water molecule. In the process of photosynthesis, glucose is formed in plants. The molecule of this substance consists of oxygen, hydrogen and carbon atoms.
What substances are called pure
If the substance contains particles of only one type, they are called pure. Water, sugar, salt, gold - these are their examples. So everyone knows firsthand about what substances are called pure (Grade 5 studies this topic in a course in natural history).
But scientists believe that in nature such a concept simply does not exist. The point is that there are simply absolutely no pure substances. All of them are soluble in water. Some are at the ion level, others are molecules. Imagine the following experience. Silver jewelry was placed in a vessel with clean water. What will happen? Purely visual - nothing, because metal cannot dissolve in water. However, silver ions are distributed between the molecules of the solvent. The result is the same water purified by silver.
Life examples
With the concepts that are discussed in our article, we come across 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. These are water, ground coffee beans and sugar. Pure substances are also necessary for making soup. Here, in addition to water, salt and oil are required, and then it’s a matter of taste.
All women love jewelry made of gold. At first glance, it may seem that this metal is an example of what substances are called pure. But it is not so. Each of these products has a sample. For example, 585. This means the amount of gold that is contained in this alloy. The rest of it is made up of 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 additives? The fact is that items made of pure gold would be soft and fragile, and therefore short-lived.
Pure substances and mixtures: what is it
The collection of individual substances is called a mixture. Its main characteristics include inconsistent composition, inconsistency of physical properties, lack of energy release during their formation.
Sweet and salty water are already mixtures. Their formation is based on the ability of solids to dissolve. But will the composition of such mixtures change if they are frozen? Not at all. In the transition 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 may not only be liquid. For example, air is a solution of gases, and alloy is a solid metal.
In heterogeneous, or heterogeneous mixtures, particles of individual substances can be distinguished with the naked eye. This is a suspension. If their composition includes 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 insoluble in each other are called emulsions. Mix water with vegetable oil. Shake the resulting solution well. As a result, droplets of oil will merge on the surface of the water into a dense film.
Methods for the separation of mixtures
The advantage of mixtures is that they acquire new, most often useful, characteristics in comparison with pure substances. But sometimes it is necessary to carry out the reverse process. As you know, oil is an excellent fuel. But if you select hydrocarbons from this mixture, then each of them can be used separately. Therefore, you can get several types of fuel, which is very profitable. 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 magnet action, settling and filtering. An example of the first method is a combination of iron and wood sawdust. This method is based on various magnetic properties of substances. Filtration is suitable for mixtures with different solubilities and particle sizes. For its implementation, a special device is used. This is the filter: cotton wool, gauze and even a strainer, which we use to make tea. If the components of the suspension have different densities, sedimentation 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 physical properties of the constituent substances, it can be homogeneous or heterogeneous.