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 enters our stomach, the substances included in the product that we have absorbed begin to interact with the 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 the methods of separation of 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 type of particles. And this is the first important property. A pure substance is water, for example, which consists solely of water molecules (that is, its 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, in contrast to mixtures, are constant and change when impurities appear. Only distilled water has a boiling point, and 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 out the mass of a pure substance? The formula for the calculation is as follows - m (mass) of pure substance = W (concentration) of pure substance * mixture / 100%.
There is also such a type of pure substances as highly pure substances (ultrapure, high-purity). Such substances are used in the manufacture 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 that which contains elements of the same kind. A good example of a pure substance is snow. 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 a daily basis, we come across 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 we will 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, but can be natural. They are in solid, liquid and gaseous state. As 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, as it appears without human involvement in the production process and contains many different components.
The mixtures created by man are almost always durable, and natural ones under the influence of heat begin to disintegrate into individual particles (milk, for example, turns sour after a few days). Mixtures are also divided into heterogeneous and homogeneous. Heterogeneous mixtures are heterogeneous, and their components are visible with the naked eye and under a microscope. Such mixtures are called suspensions, which in turn are divided into suspensions (a substance in the 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 (can be substances in a gaseous, liquid or solid state).
Characteristics of the mixture and pure substances
For convenience, information is presented in tabular form.
Comparative feature | Pure substances | Mixes |
Composition of Substances | Maintain a permanent composition | They have a variable composition |
Types of substances | Contain one substance | Include various substances |
Physical properties | Keep constant physical properties | They have inconsistent physical properties. |
The change in the energy of a substance | Changes with energy | Does not change |
Methods for producing 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 divided by sedimentation and filtration. Homogeneous mixtures are divided by evaporation and distillation. Let's consider each method separately.
Upholding
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 those substances that will be separated. For example, one heavy substance and water. What pure substances are heavier than water? This is sand, for example, which, due to its mass, will begin to sink to the bottom. In the same way, different emulsions are separated. For example, vegetable oil or oil can be separated from water. These substances during the separation process form a small film on the surface of the water. In laboratory conditions, the same process is carried out using a separatory funnel. This method of separation of mixtures also works in nature (without human intervention). For example, the deposition of soot from smoke and the settling of cream in milk.
Filtration
This method is suitable for the preparation of pure substances from heterogeneous mixtures, for example, from a mixture of water with sodium chloride. So, how does filtration work in the process of separating particles from a mixture? The bottom line is that substances have different solubility levels and particle sizes.
The filter is designed so 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 will not be able to pass through the filter and will be weeded out. 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, fired clay, pressed glass and other porous objects. Filters are used in real life much more often than it might seem.
The familiar vacuum cleaner works on this principle, which separates large particles of debris and deftly sucks small ones that are unable to damage the mechanism. When you are sick, put on a gauze bandage that can weed out bacteria. Workers whose profession is associated with the spread of hazardous gases and dust wear respiratory masks to protect them from poisoning.
Magnet and Water Exposure
In this way, a mixture of iron and sulfur powder can be separated. The principle of separation is based on the effect of a magnet on iron. Iron particles are attracted to the magnet, while sulfur will remain in place. The same method can be used to separate other metal parts from the total mass of different materials.
If sulfur powder mixed with iron powder is poured into water, then 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 salt in water. It works in vivo and laboratory conditions. For example, some lakes evaporate water when heated, and salt 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 a time. Destroyed water will turn into steam, and the remaining salt will remain in its normal state.
If the substance to be extracted (sugar, for example) melts when heated, then the water does not evaporate completely. The mixture is first heated, and then the resulting modified mixture is insisted so that the sugar particles settle on the bottom. Sometimes a more difficult task is 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 distill water. Such water (distilled) is actively used in pharmacology or in automotive cooling systems. Naturally, people distill alcohol with the same method.
Chromatography
The final separation method is chromatography. It is based on the fact that some substances tend to absorb other components of substances. This works as follows. 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 be absorbed by the paper or fabric and will creep up, but the dye will lag a little. Using this technique, the scientist M.S. Tsvet was able to separate chlorophyll (a substance that gives the green color to plants) from the green parts of the plant.