Pure substance and mixture. Chemistry

In the 8th grade, students study in the course of chemistry pure substances and mixtures. Our article will help them to understand this topic. We will tell you what substances are called pure, and which are mixtures. Have you ever thought about the question: "Is there absolutely pure substance?" Perhaps, the answer will surprise you.

Why is this topic being studied at school?

Before considering the definition of "pure substance", it is necessary to deal with the question: "With what substance do we actually deal - with pure or a mixture?"

At all times, the purity of the substance worried not only scientists, scientists, but also ordinary people. What do we usually put into this concept? Each of us wants to drink water without heavy metal impurities. We want to breathe fresh air that is not polluted by car exhausts. But can you call uncontaminated water and air pure substances? From the point of view of science - no.

What is a mixture?

So, the mixture is a substance that contains molecules of several kinds. Now think about the composition of the water that flows from the tap - yes, there are a lot of impurities in it. In turn, the substances that make up the mixture are called components. Let's consider an example. The air we breathe is a mixture of different gases. The components that make up its composition are oxygen, nitrogen, carbon dioxide and so on. If the mass of one component is tens of times smaller than the mass of the other, then such a substance is called an impurity. Often in nature there is air, which is contaminated with impurities of hydrogen sulphide. This gas has the smell of rotten eggs and is poisonous to humans. When holidaymakers on the bank of the river bred a fire, it pollutes the air with carbon dioxide, which is also dangerous in large quantities.

The particularly clever guys may already have a question: "What is more common - pure substances or mixtures?" Answering your question: "Basically everything that surrounds us is a mixture."

In such an amazing way nature is arranged.

A few words about the types of pure substances

At the beginning of the article, we promised to talk about whether there are absolutely no substances. Do you think there are such? We already talked about tap water. But can it contain impurities in the spring water? The answer to this question is simple: absolutely pure substances are not found in nature. However, in scientific circles it is customary to talk about the relative purity of matter. It sounds like this: "The substance is clean, but with a reservation". So, for example, it can be clean technically. Black and violet inks contain impurities. If they can not be detected by a chemical reaction, then such a substance is called chemically pure. This is distilled water.

About cleanliness

So, it's time to talk about pure substance. It is a substance that has only one species in its composition. It turns out that it has special properties. He has one more name: an individual substance. Let's try to characterize the properties of clean water:

• Individual substance: distilled water;
• ; The boiling point is 100 ° C ;
• ; Melting point - 0 ° C ;
• This water has no taste, smell and color.

How to separate substances?

This question is also appropriate. Very often in everyday life and at work (to a greater extent), people share substances. For example, in milk, creams are formed, which can be collected from the surface, if the settling method is applied. During oil refining, a person produces gasoline, rocket fuel, kerosene, engine oil and so on. At all stages of processing, a person uses a variety of methods for separating mixtures that depend on the aggregate state of the substance. Let's consider each of them.

Filtration

This method is used when there is a liquid substance in which insoluble solid particles are contained. For example, water and river sand. This mixture man passes through the filter. Thus, sand is retained in the filter, and clean water passes through it calmly. We rarely attach importance to this, but every day in the kitchen many townspeople pass tap water through purification filters. So to a certain extent you can consider yourself a scientist!

Defending

About this method, we said a few words a little higher. However, consider it in more detail. To this method, chemists resort to the case when it is necessary to separate suspensions or emulsions. For example, if vegetable oil has penetrated into the clean water, then the mixture should be shaken, then let it steep for a while. After that, the person will observe the phenomenon when the oil in the form of a film will cover the water.

In laboratories, chemists use another method, which is called a separatory funnel. When using this method of purification, a dense liquid penetrates into the container, and what is easier remains.

The method of settling has a serious drawback - it is a low speed of the process. In this case, it takes a long time to form a precipitate. In industrial enterprises, this method is still used. Engineers design special constructions, which are called "sedimentation tanks".

Magnet

Each of us at least once in my life played with a magnet. Its amazing property of attracting metals seemed magical. Resourceful people guessed using a magnet to separate the mixture. For example, separation of wood and iron filings is possible with a magnet. But it should be taken into account that not all metals can attract, only those mixtures containing ferromagnets are subject to it. They include nickel, terbium, cobalt, erbium and so on.

Distillation

This term has Latin roots, in translation means "dripping with drops." This method is a separation of mixtures based on differences in the boiling point of substances. It is this method that will help to separate water and alcohol. . The latter substance evaporates at +78 ° C. When its vapor touches the cold walls and surfaces, the vapor condenses, turning into a liquid substance.

In heavy industry this method produces oil products, pure metals, as well as a variety of fragrant substances.

Is it possible to separate gases?

We talked about pure substances and mixtures in the liquid and solid state. But what if the separation of gas mixtures is necessary? The bright heads of the chemical industry today practice several physical methods for the separation of gaseous mixtures:

• condensation;
• Sorption;
• Membrane separation;
• Reflux.

So, in this article we have considered the concept of pure substances and mixtures. We found out what is more common in nature. Now you know the different ways of separating mixtures - and some of them can be demonstrated on your own, for example a magnet. We hope that our article was useful to you. Study science today, so that tomorrow it helps you solve any problem - both at home and at work!