Solutions and Colligative Properties 195Second Free-Response Question
a. Solution (5) barium chloride will give a precipitate. The formula of the precipitate is
BaCrO 4.
You get 1 point for picking the correct solution, and 1 point for the correct formula for
the precipitate.
b. Solution (3) sodium carbonate is the most basic. Since the carbonate ion is the conjugate base
of a weak acid, it will undergo significant hydrolysis to produce a basic solution.
You get 1 point for picking the correct solution, and 1 point for the correct explanation.
c. Solution (2) methyl alcohol will show the least boiling point elevation. Methyl alcohol
is the only nonelectrolyte.
You get 1 point for picking the correct solution, and 1 point for the correct formula for
the explanation.
d. Solution (4) ammonium chromate is yellow.
You get 1 point for picking the correct solution.
e. Solution (2) methyl alcohol is the only solution that will not form a precipitate with
barium chloride.
You get 1 point for picking the correct solution.Rapid Review
A solution is a homogeneous mixture composed of a solvent and one or more solutes. A
solute is a substance that dissolves in the solvent and is normally present in smaller amount.
The general rule of solubility is “like dissolves like.” This means that polar solvents dis-
solve polar solutes and nonpolar solvents dissolve nonpolar solutes.
A saturated solution is one in which the maximum amount of solute is dissolved for a
given amount of solvent at a given temperature. Any solution with less than the maxi-
mum solute is called unsaturated. A solution with greater than maximum solute is super-
saturated (an unstable state).
Solution concentration may be expressed as a percentage, which is the amount of solute dis-
solved per 100 units of solvent. It may be expressed as mass %, mass/volume %, or
volume/volume %. Know how to calculate the appropriate percentage concentration for a
solution.
For the chemist the most useful unit of concentration is molarity (M), which is the
moles of solute per liter of solution. Know how to work molarity problems.
Another concentration unit is molality (m), which is the moles of solute per kilogram of
solvent. Know how to work molality problems.
Electrolytes conduct an electrical current when melted or dissolved in a solvent, whereas
nonelectrolytes do not.
Colligative properties are properties of solutions that depend simply on the number of
solute particles and not the types. Colligative properties include:- Vapor pressure lowering––The vapor pressure of the solvent is lower in a solution
than in the pure solvent. - Freezing-point depression––The freezing point of a solution is lower than that of the
pure solvent.