CLASSIFICATION AND PROPERTIES OF MATTER
INTRODUCTION
Chemistry is often defined as the study of matter. Associated with this concept of matter are
terms such as substance, compound, element, mixture, etc. Matter is also described as possessing
certain properties, e.g. smell, color. We distinguish between physical or chemical properties.
Substances can also undergo changes, some of which are classified as physical changes and others as
chemical changes. Terms such as these need to become part of the vocabulary of students who wish
to undertake a serious study of chemistry. In the following sections, definitions will be given for
these concepts and are illustrated in a series of simple exercises.
DEFINITIONS
Matter is anything that has mass and occupies space. Matter can exist in three forms or phases:
solids, liquids, or gases.
A substance is defined as matter which is homogeneous and of which all parts are alike.
Substances are either elements or compounds.
Elements are pure substances which cannot be decomposed into simpler substances by chemical
means. Some familiar elements are oxygen, gold, sulfur, and iron.
Compounds are pure substances that are composed of two or more elements. Substances such as
water, salt, and sugar are simple examples of compounds. On the other hand, wood or a piece of
marble are not homogeneous and therefore not pure substances or compounds. They are called
mixtures.
Mixtures are defined as matter which consists of two or more substances mixed together. A
mixture can be either homogeneous or heterogeneous. In a heterogeneous mixture several difference
components can be detected with the unaided eye. Marble is not homogeneous, you can see
different colored components. However, salt dissolved in water produces a perfectly homogeneous
mixture.
The relationship between the concepts introduced above is shown in Figure 1.
4
Figure 1.
Classification of Matter
It is not only necessary to define the various forms of matter but we need to be concerned
also with the characteristics or properties of matter. Furthermore, we wish to define the changes that
matter can undergo.
A physical property of matter is one that can be observed without changing its composition. Gold
is a shiny yellow metal. Lead has a high density. Observations of these characteristics do not
change the composition.
A chemical property is one which is observed when matter undergoes a transformation that results
in a change of composition. Gasoline will burn in air to form products which are very different from
the original material. Iron will rust in moist air to form a compound called iron oxide. The fact that
gasoline burns and iron rusts are therefore chemical properties.
A physical change is a change in the form of matter without changing its composition. Examples of
such changes are phase changes such as melting, boiling, etc.
A chemical change is one that leads to a change in the composition of the matter involved. The
burning of wood leads to products very different than the starting material.
Physical changes are quite often reversible. Ice can be melted to form liquid water;
however, water can be readily reconverted to ice. Chemical changes are usually irreversible.
Gasoline can be burned to produce water and carbon dioxide, but it is not possible to reconvert these
into the original material.
Even though matter can undergo changes it is important to realize that in ordinary chemical
reactions matter cannot be created or destroyed. We say that matter is conserved. This is one of the
fundamental conservation laws.
5
PROCEDURE
Part I. Mixtures
Obtain small samples of the following mixtures: dirt, river water, granite chips, air, and
brass. Examine each carefully using a magnifying lens if necessary. Make a table in your laboratory
notebook and indicate whether the mixture is homogeneous or heterogeneous. Also, give a general
description of each mixture.
Fold a piece of filter paper and place it in a filter funnel. Moisten the filter paper with
distilled water. Filter 10 mL of river water and collect the filtrate (the liquid which passes through
the filter) in an evaporating dish. Carefully heat and evaporate the filtrate. Examine the residue
obtained.
Part II. Substances
Examine small samples of each of the following: sugar, sodium chloride, and copper.
CAUTION: Consult your instructor for proper disposal of substances used. For each substance
examined enter the following into a table in your laboratory notebook:
a.Name of substance
b.Three physical properties for each
c.Effect of heat on the pure substance
d.Extent of the solubility of the pure substance in water
e.Tell whether a physical change, chemical change, or both changes took place when the
pure substance was heated.
Part III. Use of Data Tables
Much useful information on the properties of substances has been assembled. One such
compilation is the CRC Handbook of Chemistry and Physics. A copy of this is available in the
laboratory. Look up the following information for sodium chloride and record it in your laboratory
notebook.
a.Formula
b.Formula weight
c.Density
d.Melting point
e.Boiling point
f.Solubility in water at both 0oC and 100oC
6
QUESTIONS
1. What are the three general components of river water? Describe them.
1. What properties of each of the general components of river water were used to allow you to
separate the components?
2. Describe a simple experiment to show that air is a mixture.
3. If a portion of the substance used does not appear to dissolve, how could evidence be
obtained to determine if any of the substance had dissolved?
4. 5. Does sugar undergo a physical change or a chemical change when it dissolves in water?
What evidence from the experiment supports your choice?
5. What is the basic difference between a physical and a chemical change?
6. A piece of silver and a piece of platinum are both silvery, white, shiny metals. What
physical property could be used to easily distinguish silver from platinum?
(Use the CRC Handbook of Chemistry and Physics to get data to support your answer.)
7. Iodine crystals sublime, i.e. they pass directly from the solid to the gaseous state without
liquefying, Is this process a chemical change or a physical change? Why?
8. Explain how it is possible to have a heterogeneous mixture and still have only one pure
substance present. Give an example.
9. Explain how it is possible to have a homogeneous mixture of two different compounds.
Give an example.
7