LESSON 4: MIXTURES AND PURE SUBSTANCES
Classification of Matter
Pg. 57 – A material system is a collection of elements (points, particle, substances,
individuals…) related to each other, which are considered for study as if they form a unit.
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A system is homogeneous when its appearance is uniform and one can’t distinguish
different components at first sight, that is to say, when it seems to be formed from a
single substance.
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A system is heterogeneous when one can distinguish different components at first
sight, that is to say, when it seems to be formed from several substances.
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Physical processes are those that don’t change the natures of the substances.
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Mixtures are material systems from which one can separate different substances using
some physical process. Mixtures can be homogeneous and heterogeneous.
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Pure substances are material systems, usually homogeneous, from which one can’t
separate different substances using physical processes.
Pg. 58 – A heterogeneous mixture is one in which one can notice, at first sight, that it is
formed by different substances.
Pg. 59 – A homogeneous mixture is one in which one cannott notice, at first sight, that it is
formed by different substances.
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A dissolution is a homogeneous mixture made up of two or more pure substances that
are found in it in variable quantities and can be separated by physical processes.
Pg. 63 – The characteristics or specific properties of a pure substance are those that serve to
differentiate them from other pure substances.
Pg. 64 – An element is a pure substance that cannot be decomposed into other more simple
substances.
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A simple substance is one that is formed by a single element.
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A compound is a substance formed by two or more elements always combined in
fixed proportions.
Activities
1) The air held in a room is a large gaseous mass with a homogeneous appearance.
Answer the questions in your notebook and deduce their composition.
a. From where do we get the oxygen that we need to breathe?
b. Where is the CO2 (carbon dioxide) that is separated in breathing
incorporated?
c. Where can we find gases such as nitrogen and hydrogen?
d. Why do we sometimes say that there is a lot of humidity in the air?
e. Do you think that the air that we breathe is composed of a single gaseous
substance or of several different gases?
2) Are pure substances always homogeneous? Justify your answer.
3) Do you consider a piece of wood to be a heterogeneous mixture? And if you can see
(in the wood) grains of different colors?
4) Do you think that powdered detergents for washing machines are heterogeneous
mixtures? And if it contains particles of different colors? Reason out your answers.
5) Why is it necessary to analyze material systems before giving an opinion about their
compositions?
6) A soft drink contains sugar, water (H2O), carbon dioxide (CO2), orange juice,
preservatives, and colorants. Indicate which of these ingredients are the dissolvents,
which are the solutes, and in which state is each one of them?
7) Analyse the label of a bottle of mineral water. Which are the solutes that it contains?
8) What would you do separate a mixture of oil and water?
9) What would you do separate a mixture of salt and sulphur? (Sulphur is insoluble in
water.)
10) What technique is used to obtain salt in salt mines? In which physical process is it
based?
11) If you had to extract, without impurities, a solid substance dissolved in water, what
technique would you use?
12) If you wanted to separate two insoluble liquids from each other, what technique
would you use? And if the liquids were soluble?
13) What physical processes intervene when two or more substances are separated by
distillation?
14) Look up what a distillery is and what substances are obtained in distillation.
15) What do we call the characteristic properties of a pure substance?
16) We have heated a solid substance for ten minutes and we have noted the temperatures
during that time in the following table:
a. Construct with these facts the graph of changes of state of this substance.
b. What is its fusion point? And what is its boiling point?
c. Indicate the section in which there is a mixture of solid and liquid.
d. Indicate the section in which there is a mixture of liquid and gas.
17) What’s a chemical process? Reason if the dissolution of table salt in water is a
physical or chemical process.
18) When do we say that a pure substance is a compound? Is a mixture the same as a
compound?
19) Which are the basic substances with which are built all the matter that we know?
What differences are there between a simple substance and a compound?
Clear Ideas

A material system is a collection of elements related to each other, which are considered
for study as if they constitute a unit.

Material systems can be homogeneous and heterogeneous.

In a homogeneous system you can not distinguish different components at first sight.

In a heterogeneous system distinguish you can distinguish different substances at first
sight.
.
A mixture is a homogeneous or heterogeneous material system from which one can
separate different substances using physical processes.

.

A dissolution is a homogeneous mixture that is made up by two or more substances that
are found in it in variable quantities and can be separated by physical processes.

In a dissolution, the substance that is found the greatest quantity is called the solvent; the
others substances are called solutes.

In order to separate the substances that make up a mixture, you must use physical
processes that do not alter the nature of the substances.

The most common separation techniques for mixtures are sifting, filtering, magnetic
separation, decanting, crystallizing, precipitation, and distilling.

A pure substance is one whose different components cannot be separated using physical
processes.

The characteristic properties of a pure substance serve to differentiate it from other pure
substances.

The properties most often used to distinguish pure substances are their melting points,
boiling points, and densities.

Pure substances are classified into simple substances and compounds.

An element is a pure substance that can not be decomposed into other, more simple
substances.

A simple substance is one that is formed by a single element.

The elements can be combined with each other to form compounds.

A compound is a pure substance that can be decomposed into other simple substances
using chemical processes.

The principal elements in the universe are hydrogen (H) and helium (He).

The largest part of hydrogen that exists in the Earth is found combined with oxygen,
forming water.

Helium is an inert gas, that is, it does not react nor combine with other elements.