Pure substances: examples. Preparation of pure substances

Our whole life is literally built on the work of various chemicals. We breathe air, which contains many different gases. The output is carbon dioxide, which is then processed by plants. We drink water or milk, which is a mixture of water with other components (fat, mineral salts, protein and so on).

A banal apple is a whole complex of complex chemicals that interact with each other and our body. As soon as something gets into our stomach, the substances entering the product absorbed by us begin to interact with the gastric juice. Absolutely every object: man, vegetable, animal - a set of particles and substances. The latter are divided into two different types: pure substances and mixtures. In this material, we will understand what substances are pure, and which of them belong to the category of mixtures. Consider ways to separate mixtures. And also take a look at typical examples of pure substances.

Pure substances

So, in chemistry, pure substances are those substances that always consist of only one single species of particles. And this is the first important property. A pure substance is water, for example, which consists exclusively of water molecules (that is, its own). Also, a pure substance always has a constant composition. Thus, each molecule of water consists of two hydrogen atoms and one oxygen atom.

The properties of pure substances, unlike mixtures, are of a constant nature and change when impurities appear. Only distilled water has a boiling point, and the sea boils at a higher temperature. It should be taken into account that any pure substance is not absolutely pure, since even pure aluminum has an admixture in the composition, although it has a share of 0.001%. The question arises, how to determine the mass of pure matter? The formula for the calculation is as follows: m (mass) of pure substance = W (concentration) of pure substance * mixture / 100%.

Also, there is a type of pure substances, such as highly pure substances (ultrapure, high-purity). Such substances are used in the manufacture of semiconductors in various measuring and computing devices, nuclear power engineering and in many other professional fields.

Examples of pure substances

We have already found out that the pure substance is that it contains elements of the same species. A good example of a pure substance is snow. In fact, this is the same water, but unlike the water we encounter every day, this water is much cleaner and does not contain impurities. Diamond is also a pure substance, because it contains only carbon without impurities. The same applies to rock crystal. On a daily basis, we come across another example of a pure substance - refined sugar, which contains only sucrose.

Mixtures

We have already considered pure substances and examples of pure substances, now we move on to another category of substances - mixtures. A mixture is when several substances are mixed with each other. We are confronted with mixtures on an ongoing basis, even in everyday life. The same tea or soap solution is a mixture that we use daily. Mixtures can be created by humans, and can be natural. They are in a solid, liquid and gaseous state. As already mentioned above, the same tea is a mixture of water, sugar and tea. This is an example of a mixture created by man. Milk is a natural mixture, since it appears without the participation of man in the process of production and contains many different components.

Mixtures created by humans are almost always durable, and natural under the influence of heat begin to break up into separate particles (milk, for example, will sour in a few days). Mixtures are also divided into heterogeneous and homogeneous. Heterogeneous mixtures are heterogeneous, and their components are visible to the naked eye and under a microscope. Such mixtures are referred to as suspensions, which in turn are divided into suspensions (solid matter and substance in the liquid state) and emulsions (two substances in the liquid state). Homogeneous mixtures are homogeneous, and their individual components can not be considered. They are also called solutions (they can be substances in the gaseous, liquid or solid state).

Characteristics of the mixture and pure substances

For convenience of perception, the information is presented in the form of a table.

Methods for obtaining pure substances

In nature, many substances exist in the form of mixtures. They are used in pharmacology, industrial production.

To obtain pure substances, different methods of separation are used. The heterogeneous mixtures are separated by settling and filtration. Homogeneous mixtures are divided by evaporation and distillation. Let's consider each method separately.

Defending

This method is used to separate suspensions, such as a mixture of river sand with water. The main principle on which the process of upholding is based is the difference in the densities of those substances that will be separated. For example, one heavy substance and water. Which pure substances are heavier than water? This is sand, for example, which by virtue of its mass will begin to settle to the bottom. In the same way, different emulsions are separated. For example, from water it is possible to separate vegetable oil or oil. These substances in the separation process form a small film on the water surface. In the laboratory, the same process is carried out using a separatory funnel. This method of separation of mixtures works in nature (without human participation). For example, the deposition of soot from the smoke and settling cream in milk.

Filtration

This method is suitable for obtaining pure substances from heterogeneous mixtures, for example, from a mixture of water and common salt. So, how does the filtration work in the process of separating the particles of the mixture? The bottom line is that substances have different levels of solubility and particle sizes.

The filter is designed in such a way that only particles with the same solubility or the same size that it can pass through can pass through it. Larger and other unsuitable particles can not pass through the filter and will be eliminated. The role of filters can be played not only by specialized devices and solutions within the laboratory, but also by things familiar to everyone, such as cotton wool, coal, burnt clay, pressed glass and other porous objects. Filters are used in real life much more often than it may seem.

By this principle, we all use a familiar vacuum cleaner that separates large debris and deftly sucks small, incapable of damaging the mechanism. When you are sick, you put on a gauze dressing that can weed out bacteria. Workers, whose profession is associated with the spread of dangerous gases and dust, wear respiratory masks that protect them from poisoning.

Effects of magnet and water

In this way, a mixture of iron powder and sulfur can be separated. The principle of separation is based on the effect of a magnet on iron. The iron particles are attracted to the magnet, while the sulfur remains in place. The same method can be used to separate other metal parts from the total mass of different materials.

If a powder of sulfur mixed with iron powder is poured into the water, the non-wettable sulfur particles will float to the surface of the water, while the heavy iron will immediately fall to the bottom.

Evaporation and crystallization

This method works with homogeneous mixtures, such as a solution of salt in water. It works in natural natural processes and laboratory conditions. For example, some lakes evaporate water when heated, and in its place remains table salt. From the point of view of chemistry, this process is based on the fact that the difference between the boiling point of two substances does not allow them to evaporate at a time. The destroyed water will turn to steam, and the remaining salt will remain in its normal state.

If the substance that needs to be removed (sugar, for example) melts when heated, then the water does not evaporate completely. The mixture is first heated, and then the resulting modified mixture insists that the sugar particles settle on the bottom. Sometimes there is a more difficult task - to separate a substance with a higher boiling point. For example, the separation of water from salt. In this case, the evaporated substance must be collected, cooled and condensed. This method of separating homogeneous mixtures is called distillation (or simply distillation). There are special devices that distil water. Such water (distilled) is actively used in pharmacology or in automotive cooling systems. Naturally, people use this method to distill alcohol.

Chromatography

The last method of separation is chromatography. It is based on the fact that some substances have the property of absorbing other components of substances. This works as follows. If you take a piece of paper or cloth on which something is written in ink and immerse it in water, you will notice the following: the water will start to soak up with paper or cloth and crawl up, but the coloring matter will lag slightly behind. Using this technique, the scientist MS Color was able to separate chlorophyll (a substance that gives green color to plants) from the green parts of the plant.