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 ingredients (fat, mineral s alts, 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 enters our stomach, the substances included in the product absorbed by us begin to interact with gastric juice. Absolutely every object: a person, a vegetable, an animal is a set of particles and substances. The latter are divided into two different types: pure substances and mixtures. In this material, we will figure out which substances are pure, and which of them belong to the category of mixtures. Consider methods for separating mixtures. And also look at typical examples of pure substances.
Pure substances
So, in chemistry, pure substances are those substances that always consist of only one single kind of particles. And this is the first important property. A pure substance is water, for example, which consists ofexclusively from water molecules (that is, their own). Also, a pure substance always has a constant composition. Thus, each water molecule consists of two hydrogen atoms and one oxygen atom.
The properties of pure substances, unlike mixtures, are permanent and change when impurities appear. Only distilled water has a boiling point, while sea water boils at a higher temperature. It should be borne in mind that any pure substance is not absolutely pure, since even pure aluminum has an impurity in the composition, although it has a share of 0.001%. The question arises, how to find the mass of a pure substance? The formula for calculating is as follows - m (mass) of a pure substance \u003d W (concentration) of a pure substancemixture / 100%.
There is also such a type of pure substances as ultra-pure substances (ultra-pure, high-purity). Such substances are used in the production of semiconductors in various measuring and computing devices, nuclear energy and in many other professional fields.
Examples of pure substances
We have already found out that a pure substance is something that contains elements of the same kind. Snow is a good example of a pure substance. In fact, this is the same water, but unlike the water that we encounter daily, this water is much cleaner and does not contain impurities. Diamond is also a pure substance, since it contains only carbon without impurities. The same applies to rock crystal. On theOn a daily basis, we are confronted with another example of a pure substance - refined sugar, which contains only sucrose.
Mixes
We have already considered pure substances and examples of pure substances, now let's move on to another category of substances - mixtures. A mixture is when several substances are mixed together. We encounter mixtures on an ongoing basis, even in everyday life. The same tea or soap solution are mixtures that we use daily. Mixtures can be created by man, or they can be natural. They are in solid, liquid and gaseous states. As mentioned above, the same tea is a mixture of water, sugar and tea. This is an example of a man-made mixture. Milk is a natural mixture, as it appears without human intervention in the development process and contains many different components.
Mixtures created by man are almost always durable, and natural ones under the influence of heat begin to disintegrate into separate particles (milk, for example, sours after 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 called suspensions, which in turn are divided into suspensions (a substance in a solid state and a substance in a liquid state) and emulsions (two substances in a liquid state). Homogeneous mixtures are homogeneous, and their individual components cannot be considered. They are also called solutions (they can be substances in gaseous,liquid or solid state).
Characteristics of mixture and pure substances
For ease of perception, the information is presented in the form of a table.
| Comparative sign | Pure substances | Mixes |
| Composition of substances | Keep the composition constant | Have a variable composition |
| Types of substances | Contain one substance | Include various substances |
| Physical properties | Keep constant physical properties | Have unstable physical properties |
| Change in the energy of matter | Changes when energy is generated | No change |
Methods for obtaining pure substances
In nature, many substances exist as mixtures. They are used in pharmacology, industrial production.
To obtain pure substances, various separation methods are used. Heterogeneous mixtures are separated by settling and filtering. Homogeneous mixtures are separated by evaporation and distillation. Consider each method separately.
Settling
This method is used to separate suspensions such as a mixture of river sand and water. The main principle on which the settling process is based is the difference in the densities of thosesubstances to be separated. For example, one heavy substance and water. Which pure substance is heavier than water? This is sand, for example, which, due to its mass, will begin to settle to the bottom. Different emulsions are separated in the same way. For example, vegetable oil or oil can be separated from water. These substances in the process of separation form a small film on the surface of the water. Under laboratory conditions, the same process is carried out using a separating funnel. This method of separating mixtures also works in nature (without human intervention). For example, deposition of soot from smoke and settling of cream in milk.
Filtering
This method is suitable for obtaining pure substances from heterogeneous mixtures, for example, from a mixture of water and table s alt. So, how does filtration work in the process of separating the particles of a mixture? The bottom line is that substances have different solubility levels and particle sizes.
The filter is designed in such a way that only particles with the same solubility or the same size can pass through it. Larger and other unsuitable particles will not be able to pass through the filter and will be screened out. The role of filters can be played not only by specialized devices and solutions within the laboratory, but also by familiar things such as cotton wool, coal, baked clay, pressed glass and other porous objects. Filters are used in real life much more often than you might think.
According to this principle, the familiar vacuum cleaner works for all of us, which separates largedebris particles and deftly sucks up small ones that are unable to damage the mechanism. When you are sick, you wear a gauze bandage that can weed out bacteria. Workers whose profession is associated with the spread of dangerous gases and dust wear respiratory masks to protect them from poisoning.
Impact of magnet and water
This way you can separate the mixture of iron powder and sulfur. 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 a mass of different materials.
If sulfur powder mixed with iron powder is poured into water, non-wettable sulfur particles will float to the surface of the water, while heavy iron will immediately fall to the bottom.
Evaporation and crystallization
This method works with homogeneous mixtures such as a solution of s alt in water. It works in natural processes and laboratory conditions. For example, some lakes, when heated, evaporate water, and table s alt remains in its place. 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 the same time. The destroyed water will turn into steam, and the remaining s alt will remain in its normal state.
If the substance to be extracted (sugar, for example) melts when heated, the water is not completely evaporated. The mixture is first heated, and then the resulting modifiedthe mixture is insisted so that the sugar particles settle to the bottom. Sometimes there is a more difficult task - the separation of a substance with a higher boiling point. For example, separating water from s alt. 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 distill water. Such water (distilled) is actively used in pharmacology or in automotive cooling systems. Naturally, people use the same method to distill alcohol.
Chromatography
The last separation method is chromatography. It is based on the fact that some substances tend to absorb other components of substances. It works like this. If you take a piece of paper or fabric on which something is written in ink and immerse part of it in water, you will notice the following: the water will begin to be absorbed by the paper or fabric and will creep up, but the coloring matter will lag behind a little. Using this technique, the scientist M. S. Tsvet was able to separate chlorophyll (a substance that gives green color to plants) from the green parts of the plant.
