Chapter 4.pdf

Figure 4.9 A chocolate chip cookie
is a mechanical mixture. Different
parts of the mixture are visible.
Mixtures
A mixture is a combination of pure substances. However, the
substances in a mixture do not combine chemically as happens
when a compound forms. Each substance remains in its original,
pure form, although each is not always easy to see distinctly once
the mixture is made. There are three main types of mixtures.
• In a mechanical mixture, the different substances that
make up the mixture are visible (Figure 4.9). Soil is an
example of a mechanical mixture. So is a mixture of salt and
pepper. A mixture in which the different parts are visible is
called heterogeneous. The prefix “hetero-” means different.
•A suspension is a cloudy mixture in which tiny particles of
one substance are held within another (Figure 4.10).
Tomato juice is an example of a suspension. These particles
can be separated out when the mixture is poured through
filter paper. A suspension is also a heterogeneous mixture.
• In a solution, the different substances that make it up are
not individually visible (Figure 4.11). One substance is
dissolved in another, creating a homogeneous mixture. The
prefix “homo-” means same, and all parts of a homogeneous
mixture look the same. Examples of solutions are sugar
dissolved in hot coffee, and acetic acid dissolved in water to
make vinegar.
Figure 4.10 A salad vinaigrette is a mixture of oil, vinegar, and
spices. When shaken, they form a suspension. After a while, the
components will separate. This is why salad dressings are
usually shaken before using.
Figure 4.11 Tea is a solution of water and the extract of tea
leaves that are dissolved in the water. A solution is
homogeneous. Every part of the tea looks like every other part.
142 UNIT B Atoms, Elements, and Compounds