In the 8th grade, students study pure substances and mixtures in a chemistry course. Our article will help them understand this topic. We will tell you which substances are called pure, and which are called mixtures. Have you ever thought about the question: “Is there an absolutely pure substance?” The answer may surprise you.
Why is this topic taught in school?
Before considering the definition of a "pure substance", it is necessary to deal with the question: "Which substance are we really dealing with - a pure substance or a mixture?"
At all times, the purity of matter worried not only researchers, scientists, but also ordinary people. What do we usually mean by this concept? Each of us wants to drink water without impurities of heavy metals. We want to breathe fresh air that is not polluted by car exhaust. But can unpolluted water and air be called pure substances? Scientifically, no.
What is a mixture?
So, a mixture is a substance that contains several types of molecules. Now think about the composition of the water that flowsfrom the tap - yes, yes, it has a lot of impurities. In turn, the substances that make up the mixture are called components. 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 ten times less than the mass of another, then such a substance is called an impurity. Often in nature there is air that is polluted with impurities of hydrogen sulfide. This gas smells like rotten eggs and is poisonous to humans. When vacationers make a fire on the river bank, it pollutes the air with carbon dioxide, which is also dangerous in large quantities.
Particularly quick-witted guys may already have a question: “Which is more common - pure substances or mixtures?” To answer your question: “Basically everything around us is mixtures.”
Nature is so amazing.
A few words about the types of pure substances
At the beginning of the article, we promised to talk about whether substances exist absolutely without impurities. Do you think there are such? We have already talked about tap water. But can spring water contain impurities? The answer to this question is simple: absolutely pure substances do not occur in nature. However, in scientific circles it is customary to talk about the relative purity of a substance. It sounds like this: "The substance is pure, but with a caveat." So, for example, it can be technically clean. Black and purple inks contain impurities. If they cannot be detected by a chemical reaction, then thisthe substance is said to be chemically pure. This is distilled water.
About cleanliness
So, it's time to talk about pure matter. This is a substance that in its composition has particles of only one type. It turns out that it has special properties. It has another name: individual substance. Let's try to characterize the properties of pure water:
- individual substance: distilled water;
- boiling point - 100°C;
- melting point - 0°C;
- this water has no taste, smell or color.
How to separate substances?
This question is also relevant. Very often in everyday life and at work (to a greater extent) a person separates substances. So, for example, cream is formed in milk, which can be collected from the surface if the settling method is used. During the refining of oil, a person produces gasoline, rocket fuel, kerosene, machine oil, and so on. At all stages of processing, a person uses a variety of methods for separating mixtures, which depend on the state of aggregation of the substance. Let's take a look at each one.
Filtering
This method is used when there is a liquid substance that contains insoluble solid particles. For example, water and river sand. This mixture is passed through a filter. Thus, the 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 city dwellers run tap water throughcleaning filters. So to a certain extent, you can consider yourself a scientist!
Settling
We said a few words about this method just above. However, let's consider it in more detail. Chemists resort to this method when it is necessary to separate suspensions or emulsions. For example, if vegetable oil has penetrated clean water, then the resulting mixture must be shaken, then let it brew for a while. After that, a person will observe a phenomenon when the oil in the form of a film covers the water.
In laboratories, chemists use another method called a separating funnel. When using this method of purification, a dense liquid penetrates into the container, and what is lighter remains.
The settling method has a serious drawback - it is a low speed of the process. In this case, a long time is needed for the formation of a precipitate. In industrial enterprises, this method is still used. Engineers design special structures that are called "sumps".
Magnet
Each of us played with a magnet at least once in our lives. Its amazing ability to attract metals seemed magical. Resourceful people guessed to use a magnet in order to separate mixtures. For example, the separation of wood and iron filings is possible with a magnet. But it is worth considering that it can not attract all metals, only those mixtures that contain ferromagnets are subject to it. These include nickel, terbium, cob alt, erbium andetc.
Distillation
This term has Latin roots, in translation means "draining drops." This method is the separation of mixtures based on differences in the boiling point of substances. It is this method that will help separate water and alcohol. The last substance evaporates at +78°C. When its vapors touch cold walls and surfaces, the vapors condense, turning into a liquid substance.
In heavy industry, oil products, pure metals, and various fragrant substances are extracted by this method.
Can gases be separated?
We talked about pure substances and mixtures in liquid and solid state. But what if it is necessary to separate gas mixtures? The bright heads of the chemical industry today practice several physical methods for separating gaseous mixtures:
- condensation;
- sorption;
- membrane separation;
- reflux.
So, in our 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 to separate mixtures - and you can demonstrate some of them yourself, such as a magnet. We hope that our article was useful for you. Learn science today so that tomorrow it will help you solve any problem - both at home and in production!
