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Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
149
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 14
Example Problem 14-7
Changes in Boiling and Freezing Points
What are the boiling point and freezing point of a 0.750m aqueous
solution of the electrolyte potassium bromide (KBr)?
Find the effective solute particle concentration. Each formula unit of
KBr dissociates into two ions, so the given molality must be doubled.
2 ϫ 0.750m ϭ 1.50m
Substitute the known values and solve.
⌬T b ϭ K b m ϭ (0.512°C/m) ϫ 1.50m ϭ 0.768°C
The solution’s boiling point is 100.0°C ϩ 0.768°C ϭ 100.768°C.
Substitute the known values and solve.
⌬T f ϭ K f m ϭ (1.86°C/m) ϫ 1.50m ϭ 2.79°C
The solution’s freezing point is 0.0°C Ϫ 2.79°C ϭ Ϫ2.79°C.
Practice Problems
16. What are the boiling and freezing points of a 1.34m water
solution of calcium chloride (CaCl 2 )?
17. Calculate the molality of a water solution of a nonelectrolyte,
given that the freezing point depression of the solution is 4.33°C.
Another colligative property is osmotic pressure, a pressure related
to a process called osmosis. Osmosis is the diffusion of solvent particles across a semipermeable membrane from an area of lower
solute concentration to an area of higher solute concentration. The
osmotic pressure effect is due to the fact that a smaller amount of
solute on the less concentrated side of the membrane results in a
larger number of solvent molecules available at that surface of the
membrane. Thus, there is more diffusion of solvent from the side of
lower solute concentration.
14.4 Heterogeneous Mixtures
In a true solution, which is a homogeneous mixture, the solute
particles are less than 1 nm in diameter and remain distributed
throughout the solution in a single phase. In contrast, a heterogeneous mixture contains materials that exist in distinct phases. In one
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
149
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 14
Example Problem 14-7
Changes in Boiling and Freezing Points
What are the boiling point and freezing point of a 0.750m aqueous
solution of the electrolyte potassium bromide (KBr)?
Find the effective solute particle concentration. Each formula unit of
KBr dissociates into two ions, so the given molality must be doubled.
2 ϫ 0.750m ϭ 1.50m
Substitute the known values and solve.
⌬T b ϭ K b m ϭ (0.512°C/m) ϫ 1.50m ϭ 0.768°C
The solution’s boiling point is 100.0°C ϩ 0.768°C ϭ 100.768°C.
Substitute the known values and solve.
⌬T f ϭ K f m ϭ (1.86°C/m) ϫ 1.50m ϭ 2.79°C
The solution’s freezing point is 0.0°C Ϫ 2.79°C ϭ Ϫ2.79°C.
Practice Problems
16. What are the boiling and freezing points of a 1.34m water
solution of calcium chloride (CaCl 2 )?
17. Calculate the molality of a water solution of a nonelectrolyte,
given that the freezing point depression of the solution is 4.33°C.
Another colligative property is osmotic pressure, a pressure related
to a process called osmosis. Osmosis is the diffusion of solvent particles across a semipermeable membrane from an area of lower
solute concentration to an area of higher solute concentration. The
osmotic pressure effect is due to the fact that a smaller amount of
solute on the less concentrated side of the membrane results in a
larger number of solvent molecules available at that surface of the
membrane. Thus, there is more diffusion of solvent from the side of
lower solute concentration.
14.4 Heterogeneous Mixtures
In a true solution, which is a homogeneous mixture, the solute
particles are less than 1 nm in diameter and remain distributed
throughout the solution in a single phase. In contrast, a heterogeneous mixture contains materials that exist in distinct phases. In one