Section 2.3
Classifying Matter
Objectives
1. To learn to distinguish between mixtures and pure
substances.
2. To identify homogeneous and heterogeneous mixtures.
Question:
Does matter most commonly occur as pure substances or
mixtures?
Section 2.3
Classifying Matter
A. Mixtures and Pure Substances
• Matter can be classified as a mixture or a pure
substance.
Section 2.3
Classifying Matter
A. Mixtures and Pure Substances
Mixtures
• Combination of 2 or more pure substances (elements
and compounds)
Examples: wood, gasoline, soil, air
• Variable composition –the proportions of the
components of the mixture can vary
Examples: Milk – whole, 1 %, 2 %, skim, lowfat, etc.
Section 2.3
Classifying Matter
Mixtures
• Can be separated into individual pure substances by
physical methods.
Mixtures
Homogeneous
Heterogeneous
Homogeneous – visibly indistinguishable parts (a solution)
Heterogeneous – visibly distinguishable parts
Section 2.3
Classifying Matter
Mixtures
Examples of Homogeneous Mixtures:
• Air – solution of gases (nitrogen, oxygen, carbon dioxide,
helium, argon, etc.)
• Wine – solution of liquids (water, ethanol, etc.)
• Brass – solution of metals (copper and zinc)
• Saltwater – water and salts
Examples of Heterogeneous Mixtures
• Sand and water
• Sedimentary rock
Section 2.3
Classifying Matter
A. Mixtures and Pure Substances
Pure Substances
• A pure substance always has the same composition.
• Pure substances are of two types:
– Elements which cannot be
broken down chemically
into simpler substances
– Compounds which can be
chemically broken down
into elements
Water is a compound. All the
components are the same—H2O molecules.
Section 2.3
Classifying Matter
Separation of Mixtures
• Mixtures can be separated into pure substances by
various means.
• Separations are based on differences in physical
properties
• magnetism
• mass
• solubility
• states of matter
• boiling point
• size
Section 2.3
Classifying Matter
B. Separation of Mixtures
• distillation
•Can be used to separate homogeneous liquid mixtures
•Mixtures are separated because parts of the mixture have different
boiling points
Section 2.3
Classifying Matter
B. Separation of Mixtures
• filtration
•Can be used to separate
heterogeneous solid, liquid,
and gas mixtures
•Used to separate solids
from mixtures
Section 2.3
Classifying Matter
Separation of a Mixture
Crystallization
Description: A liquid solution is heated until the liquid boils.
Solids are left behind.
For example, a saltwater solution can be separated by
heating the solution in a beaker on a hotplate. The water
evaporates and solid salt is left behind on the beaker.
• Used to separate homogeneous or heterogeneous liquid
mixtures.
• Parts of a mixture are separated because they have
different boiling points
Section 2.3
Classifying Matter
Separation of a mixture
Chromatography
Description: Many types of mixtures can be separated by
passing the mixture through a porous substance.
For example, the ink pigments that are mixed together to
make black ink can be separated by spotting the ink on a
piece of filter paper and inserting the paper into a beaker
of water.
• Mixtures are separated because the parts of a mixture
move at different speeds through a porous substance.
Section 2.3
Classifying Matter
Summary: The Organization of Matter