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16. PURE SUBSTANCES AND MIXES. DIVISION OF MIXES.
For studying of properties of substance, it is necessary to purify this substance. In the nature there are no pure substances, they meet in the form of mixes. Mixes can be divided into two big groups: homogeneous and heterogeneous.
| MIXES | |
| Homogeneous (homogeneous) | Heterogeneous (heterogeneous) |
| Homogeneous call such mixes in which particles cannot be found visually, by means of optic instruments as substances are in the shattered state at the microlevel | Heterogeneous call mixes in which particles can be found or visually, or by means of optic instruments. And these substances are in different aggregate states (phases) |
| Examples of mixes | |
| Molecular solutions (sodium chloride + water, alcohol solution in water) | Suspensions (firm + liquid), for example water + sand |
| Solid solutions, alloys, for example, brass, bronze. | Emulsions (liquid + liquid), for example water + fat |
| Gas solutions (mix of any quantities and any number of gases) | Aerosols (gas + liquid), for example fog |
| Ways of division of mixes | |
| Distillation (water-sodium chloride) | Filtering (water-sand) |
| Crystallization (water-sugar) | Upholding (water-chalk) |
| Evaporation (water-sodium chloride) | Centrifuging (water-chalk) |
| Distillation (oil) | Magnetic separation (iron-copper) |
Here only the small number of methods of division of mixes is presented.
Pure call substances which by means of physical methods are not divided into two or more other substances and do not change the physical properties.
In the nature there are no absolutely pure substances. For example, especially pure aluminum contains 0,001% of impurity. Thus, absolutely pure substance is abstraction. But chemists have to aim at receiving purer substance. You already know that one of problems of chemistry is receiving pure substances.
The Hiichesky industry releases reactants of different degree of purity. So for preparation of cooling mixtures it is reasonable to use technical NaCl sodium chloride whereas for studying of chemical properties, it is necessary to take chemically pure reactant.