A mixture is a combination of two or more substances in which each substances's
identity is retained. Mixtures are subdivided into two categories: homogeneous
mixtures and heterogeneous mixtures.
are solutions which have uniform composition and appearance throughout. A solution
may be gaseous (eg - air), solid (eg - brass) or liquid (eg - seawater). If
a spoonful of sugar is dissolved in a glass of water, the composition of the
sugar solution becomes the same in the glass. The sugar will not settle out
and every spoonful of sugar solution that is removed from the glass will have
the same composition. If the water in the glass is evaporated to dryness, the
sugar retains its identity and can be recovered.
Heterogeneous mixtures are mixtures
that do not have uniform composition and appearance throughout. The individual
components which make up the mixture remain physically separated and can be
seen as separate components. If a spoonful of sand is introduced in a glass
of water, even after considerable stirring, the sand will settle to the bottom
of the glass. Visually, the sand will separate out and the composition of sand
in the glass will be the greatest at the bottom of the glass. Any attempts to
withdraw spoonfuls of sand and water will have varying composition of each substance.
and Properties of Matter..p52