CHAPTER
13
Solutions and
Colligative Properties
IN THIS CHAPTER
Summary: A solution is a homogeneous mixture composed of a solvent and one or
more solutes. The solvent is the substance that acts as the dissolving medium and
is normally present in the greatest amount. Commonly the solvent is a liquid, but it
doesn’t have to be. Our atmosphere is a solution with nitrogen as the solvent; it is
the gas present in the largest amount (79%). Many times, you will be dealing with a
solution in which water is the solvent, an aqueous solution. The solute is the sub-
stance that the solvent dissolves and is normally present in the smaller amount. You
may have more than one solute in a solution. For example, if you dissolved table salt
(sodium chloride) and table sugar (sucrose) in water, you would have one solvent
(water) and two solutes (sodium chloride and sucrose).
Some substances will dissolve in a particular solvent and others will not. There
is a general rule in chemistry that states that “like dissolves like.” This general
statement may serve as an answer in the multiple-choice questions, but does not
serve as an explanation in the free-response questions. This simply means that
polar substances (salts, alcohols, etc.) will dissolve in polar solvents such as water,
and nonpolar solutes, such as iodine, will dissolve in nonpolar solvents such as
carbon tetrachloride. The solubility of a particular solute is normally expressed in
terms of grams solute per 100 mL of solvent (g/mL) at a specified temperature.
The temperature must be specified because the solubility of a particular sub-
stance will vary with the temperature. Normally, the solubility of solids dissolv-
ing in liquids increases with increasing temperature, while the reverse is true for
gases dissolving in liquids.
A solution in which one has dissolved the maximum amount of solute per
given amount of solvent at a given temperature is called a saturated solution.