In the 8th grade, students learn 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 absolutely pure substance?” Perhaps the answer will surprise you.
Why is this topic studied at school?
Before considering the definition of “pure substance”, it is necessary to understand the question: “What substance are we really dealing with - pure or mixture?”
At all times, the purity of matter worried not only scientists, scientists, but also ordinary people. What do we usually put in this concept? Each of us wants to drink water without impurities of heavy metals. We want to breathe fresh air, which is not polluted by car exhaust. But can clean water and air be called unpolluted? From the point of view of science - 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 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. 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 contaminated with impurities of hydrogen sulfide. This gas has the smell of rotten eggs and is toxic to humans. When vacationers on the river bank make a fire, it pollutes the air with carbon dioxide, which is also dangerous in large quantities.
Particularly ingenious guys may already have a question: “What is more common - pure substances or mixtures?” We answer your question: "Basically, everything that surrounds us is mixtures."
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 substances exist absolutely without impurities. Do you think there are any? We have already talked about tap water. 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 matter. It sounds like this: "The substance is clean, but with a reservation." So, for example, it can be technically pure. Black and violet inks contain impurities. If they cannot be detected by a chemical reaction, then such a substance is called chemically pure. This can be 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 kind. 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 ;
- such water has no taste, odor or color.
How to separate substances?
This question is also relevant. Very often in everyday life and in production (to a greater extent) a person shares substances. So, for example, cream forms in milk, 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, which depend on the state of aggregation of the substance. Let's consider each of them.
Filtration
This method is used when there is a liquid substance that contains insoluble solid particles. For example, water and river sand. A person passes such a mixture through a filter. Thus, sand lingers in the filter, and clean water passes quietly through it. We rarely attach importance to this, but every day in the kitchen, many citizens pass tap water through purification filters. So to a certain extent you can consider yourself a scientist!
Upholding
We said a few words about this method a little higher. However, 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 into clean water, then the resulting mixture must be shaken, then let it brew for a while. After that, a person will observe the phenomenon when the oil in the form of a film covers the water.
In laboratories, chemists use another method called a separatory funnel. When using this method of purification, a dense liquid enters the container, and what is easier remains.
The sedimentation method has a serious drawback - it is a low rate of the process. In this case, a long time is necessary for the formation of sediment. In industrial enterprises, this method is still used. Engineers design special structures that are called "settlers".
Magnet
Each of us has played with a magnet at least once in a lifetime. Its amazing ability to attract metals seemed magical. Resourceful people guessed to use a magnet in order to separate the mixture. For example, the separation of wood and iron filings is possible with a magnet. But it is worth considering that not all metals can attract it; only those mixtures containing ferromagnets are subject to it. These include nickel, terbium, cobalt, erbium, and so on.
Distillation
This term has Latin roots, which means “dripping”. This method is the separation of mixtures based on differences in the boiling point of substances. This method will help to 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, this method produces oil products, pure metals, as well as a variety of aromatic substances.
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 the separation of gaseous mixtures:
- condensation;
- sorption;
- membrane separation;
- reflux
So, in our article we examined the concept of pure substances and mixtures. We found that it is more common in nature. Now you know the different ways of separating mixtures - and some of them you can demonstrate yourself, for example, a magnet. We hope that our article was useful to you. Study science today so that tomorrow it will help you solve any problem - both at home and in production!