Structure of matter: elements, compounds and mixtures. Separation m...

Everything that surrounds us is matter: the computer where we read, the table on which we rely, the water we drink, the air we breathe ... we can define matter as that which occupies a place in space and can be to weigh.

Pure substances and mixtures

There are many pure substances: water, iron, cooking salt, oxygen, sugar, butane, among others. others have less familiar names, such as sulfuric acid, calcium carbonate, benzene, among others.

A pure substance is one that can not be decomposed into other more elementary by simple physical procedures and has a composition and fixed properties throughout its mass. Now, in the world around us, pure substances are not usually found alone, but forming mixtures.

If the components of a mixture are not distinguished by the naked eye, the mixture is called homogeneous (air, sea water, gasoline). the solutions are homogeneous mixtures. in a chocolate shake, you can not distinguish milk (liquid) from chocolate powder (solid), it is a homogeneous mixture.

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* If it is possible to distinguish the components at a glance, the mixture is called heterogeneous. in the granite we appreciate its components because they are of different colors, it is a heterogeneous mixture.

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### Natural and artificial substances

Classifying substances according to whether they are considered natural or artificial is a difficult task because the borders between one and the other are very diffuse. It is clear that there are substances that are natural because they exist in nature, as is the case of water. But, next to all of them, today substances are manufactured in the laboratory. They are synthetic substances. Some of these, although they already exist in nature, are synthesized in the laboratory. Others are totally new substances that have no equal reference in nature, as with some plastics or medicines.

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The water, sand or wood of the palm tree are examples of natural substances.

## Elements and compounds

Water is a pure substance, it does not change its composition in the three physical states. When we pass an electric current through it, it is transformed into two gases: oxygen and hydrogen. This procedure is called electrolysis. Therefore, water, which is a pure substance, is also a compound because it can be decomposed into simpler substances.

You can also break down some substances if they get hot. The procedure is called thermal decomposition. For example, if we heat potassium chlorate, which is a solid, we obtain oxygen and potassium chloride, also solid. Pure substances that can be broken down into simpler substances are called compounds (such as water and potassium chlorate).

Pure substances that can not be broken down by any procedure are called elements (such as oxygen or hydrogen).

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Thermal decomposition of potassium chlorate.

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Water electrolysis.

Mixtures. Separation methods

How can we separate the pure substances that are present in a mixture? We will use different separation methods, depending on the properties of the pure substances that are part of a mixture.

Properties of matter

All matter occupies a volume, has a mass and is at a temperature. Volume, mass and temperature are general properties of matter and do not serve to know the kind of matter of which the bodies are made. Por example:

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They have the same mass (100g), but it is not the same material. They can be differentiated by the smell, and they do not have the same flavor either. and you are...

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They have the same volume (1l), but it is not the same matter. They can be differentiated by density.

To differentiate one substance from another, we must resort to other properties, which are called characteristic properties, such as color, smell, magnetism, solubility, density and many others that we will study later.

The characteristic properties of several mixed substances can not be ascertained. To know them it is necessary to separate them; that is, obtain pure substances.

Some properties of matter

General: mass, volume, temperature ...
Characteristics: density, color, solubility ...

Separation of the components

A series of separation methods or methods are used to separate the components of a mixture.

If we want to separate two solids we use the sieve, which allows the separation of solid particles of different sizes. it is used with heterogeneous mixtures with solid components.

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Sieve.

* If what you want to separate are two liquids, the technique to be used is different if they are miscible (that can be dissolved) or immiscible (that can not be dissolved between them).

When the liquids are immiscible decantation is used.

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Decanting

When the liquids are miscible, for example alcohol and water, distillation is used.

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Distillation

* If what you want to separate is a solid of a liquid, you should also take into account the solubility of one in another. if the solid is soluble, it is a solution; the solvent can be evaporated and the solute is obtained as a dry residue.