CLASSIFICATION OF MATTER
Pure substances and mixtures
Mixtures and pure substances
This topic is about how materials are classified according to their chemical
composition. Substances can be: pure substances and mixtures. Define each of
the types of substances and several examples: also specify the properties of each
of the types and exercises work as an example.
Most of the material things are mixtures. For example, a lemonade is a mixture of
sugar, water and lemon juice.
What is a substance?
A substance is any variety of matter of definite and recognizable. The substances
are classified as pure substances and mixtures.
What is a pure substance?
A pure substance is a homogeneous material which always has the same
composition fixed and unchanging and whose physical and chemical properties are
the same, these substances are composed of particles (atoms or molecules)
equal. Pure substances have specific properties such as density, temperature
remains constant state changes boiling and melting temperature), solubility,
thermal and electrical conductivity properties and many more. To distinguish a pure
substance we rely on other properties.
Pure substances in turn are classified into simple and compound substances
substances. In simple
substances are
the
chemical
elements,
and
composite substances are chemical compounds.
Simple substances can be molecular or atomic, and do not decompose into
substances other. Example: oxygen, nitrogen.
Elements are pure substances simpler. Consist of the same atoms, and may not
decompose. They are represented by symbols.
Ozone (O3 ) and molecular oxygen (O2 ) are formed by oxygen atoms. Example:
copper plates, are only formed by copper atoms.
The compounds are formed and these molecules are formed by bonding of atoms
of different elements. All molecules of the same compound are equal. The
chemical compounds can be separated by chemical means. Example: For
example, 1g. sodium chloride always contains 0.3932 gr. Of sodium and 0.607 g
of chlorine.
REPRESENTATION OF SUBSTANCES:
To represent the substances used formulas, which are combinations of chemical
element symbols and numbers are placed as subscripts and indicate how
many atoms of each type are in a molecule or crystal substance. Examples:
SUBSTANCE
FORMULATES
COMPOSITION
Methane
CH4
One atom of C and four
atoms of H
Oxygen
O2
Two atoms of oxygen
WHAT HAPPENS WHEN TWO SUBSTANCES TOGETHER?
If we let the gas out a hydrogen balloon, is mixed with air without undergoing any
transformation. However, if a match in turn on the mouth of the balloon will hear a
small explosion, because the hydrogen combines with oxygen in the air and form a
new substance: water.
In one combination, the components lose their properties as a result of chemical
transformation.
In a mixture, the properties of its components unchanged and these can be
separated by physical means.
MIXTURES
When two or more basic substances are mixed and chemically combine, appears a
mixture. A mixture can be separated into its components (substances) simply by
physical methods. These can be classified into homogeneous and heterogeneous.
Heterogeneous mixtures: not uniform, in some cases, the discontinuity can be
observed with the naked eye (salt and coal, for example), in other cases, a higher
resolution to be used to monitor the discontinuity.
Homogeneous mixtures: they are completely smooth (no discontinuities occur at
ultramicroscope) and have the same properties and composition throughout the
system, some examples are the brine, the air. These mixtures are called
homogeneous solutions.
The threshold at which heterogeneous systems are distinguished from
homogeneous systems it is precisely the ultramicroscope. Different homogeneous
systems that constitute the heterogeneous system are called phases.
Large number of methods exist for separating components of a mixture, in fact,
each blend will involve the use of one or more specific methods for separation into
individual components. Only briefly describe some of these methods:

Filtering can separate suspended solids in a liquid. Involves the passage of the
liquid through a filter, a glass plate, etc..

Distillation: allows the separation of substances of different boiling
point. Consists in evaporation processes - condensation in which the vapor
phase is enriched in the more volatile component.

Dissolution: allows to separate a soluble solid in a liquid other than not.

Starring: separating substances of different solubility in another phase. Other
phase consists of adding to the system in which a large proportion is dissolved
in a substance of the original system.
A more sophisticated extension of the last two methods, what is chromatography.