What is a pure substance?

A pure substance refers to an element or compound that has no component of another compound or element. The pure substances consist of a single type of atom or molecule. Hydrogen gas and pure iron are examples of pure substances. Hydrogen is made up of hydrogen atoms only while iron consists only of iron atoms. Mixing two pure substances produces a mixture. To separate the two, scientists use a method known as filtration. The mixtures can be homogeneous or heterogeneous. The measure used to determine how much a substance can be defined as purity. In addition to hydrogen and iron, other pure substances include gold, diamonds, sugar and sodium bicarbonate.

The identification of a pure substance

There are four distinct ways to determine the purity of a substance: boiling points, melting points, electrical conductivity and chemical reactions. When a pure substance is exposed to a specific temperature condition, the environment and pressure are able to undergo definite changes that are unique and recognizable. Pure substances have a specific boiling point and a specific melting point. As for the electrical conductivity, the copper used in electrical connections must be pure. A substance like purely liquid water is a very poor conductor of electricity due to the lack of electrolytes that contribute to the conduction of electricity. During chemical reactions, pure substances form predictable products over and over again.

Degree of purity of a substance

The degree of purity of a substance is only a measure of the extent to which impure substances are present in a substance. It is now clear that a change in characteristics such as boiling points, however slight, is an indication of the presence of some other substance in that substance. Substances that interfere with the purity of a substance are called impurities. Water, for example, has a boiling point of 100 ° C and a melting point of 0 ° C. Any change in these values ​​denotes the presence of an impurity. The melting point of a substance should always be similar to its freezing point. When there is a variation, impurities should be suspected. The melting and boiling points of pure substances are always clear.

Effects of impurities on pure substances

There are four properties that impurities exude on pure substances. The properties are collectively called colligative properties. The impurities increase the boiling point of a substance, lower its freezing point, decrease the vapor pressure or cause the fluid to exert a greater osmotic pressure. If mixed with other substances, the freezing point of the water drops. This principle helps to cool various substances at temperatures below the freezing point of water. Another application of the phenomenon of impurities is in areas that experience very low temperatures during the winter. Salts spread on the roads to increase the melting of ice. Moreover, the seas, due to their brackish nature, they are not able to freeze even when other water bodies freeze due to very low temperatures. Thus, the knowledge of the pure substance is fundamental in thermodynamics, in chemical reactions and in typical daily life.


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