29 / 123
Types of mixtures
The combinations of pure substances shown in
Figure 19
are both mixtures, despite
their obvious visual differences. Mixtures can be defined in different ways and are
classified as either heterogeneous or homogeneous.
A
heterogeneous mixture
is a mixture that does not blend smoothly throughout and in
which the individual substances remain distinct. The salad dressing mixture is an
example of a heterogeneous mixture. Its composition is not uniform—the substances
have not blended smoothly and remain distinct. We can therefore say that the exis-
tence of two or more distinct areas indicates a heterogeneous mixture.
A
homogeneous mixture
is a mixture that has constant composition throughout; it
always has a single phase. If you cut two pieces out of a silver-mercury amalgam, their
compositions will be the same. They will contain the same relative amounts of silver
and mercury, no matter the size of each piece.
Homogeneous mixtures are also referred to as
solutions.
You are probably most familiar
with solutions in a liquid form, such as tea and lemonade, but solutions can be solids,
liquids, or gases. They can be a mixture of a solid and a gas, a solid and a liquid, a gas
and a liquid, and so on.
Table 5
lists the various types of solution systems and examples.
The solid-solid solution known as steel is called an alloy. An alloy is a homogeneous mixture
of metals, or a mixture of a metal and a nonmetal in which the metal substance is the major
component. For instance, steel is a mixture of iron and carbon. Adding carbon atoms
increases the hardness of the metal.
Manufacturers combine the properties of various metals in an alloy to achieve greater
strength and durability in their products. Jewelry is often made of alloys such as bronze,
sterling silver, pewter, and 14-karat gold.
Table 5
Types of Solution Systems
System
Example
Gas-gas
Air in a scuba tank is primarily a mixture of nitrogen, oxygen, and argon gases.
Gas-liquid
Oxygen and carbon dioxide are dissolved in seawater.
Liquid-gas
Moist air exhaled by the scuba diver contains water droplets.
Liquid-liquid
When it is raining, fresh water mixes with seawater.
Solid-liquid
Solid salts are dissolved in seawater.
Solid-solid
The air tank is made of an alloy—a mixture of two metals.
Get It?
LIST
six examples of solutions that you encounter as you go through your daily
activities. Indicate the system to which each belongs.
Lesson 4 • Mixtures of Matter
69