Solutions to Chapter 12 Practice Problems (Watts).
Note: these are my solutions. I have worked them out and typed them from scratch,
which takes me a lot of time and effort. They have not been copied from the textbook
publisher’s materials.
Problem 1
Strictly, none of them, I would say. Answer (b) is close: the density of water is about 1 g/
mL and the volume due to the CH3OH is a small fraction of the solution volume.
Problem 10
No. At any temperature, the mole fraction of the more volatile component in the vapor is
greater than its mole fraction in the solution. Conversely, the mole fraction of less volatile
component in the vapor is less than its mole fraction in the solution.
Problem 11
A colligative property is one that depends on the number of solute particles present, but
not the identity of the solute particles.
Properties of a solution which are not colligative: density; vapor pressure (except in the
case of a non-volatile solute).
Chief colligative properties discussed in this chapter: vapor pressure of a solution with a
non-volative solute; boiling point elevation; freezing point depression; osmotic pressure.
Density of a solution is not a colligative property. It will depend on the molar mass of the
solute, so it depends on the identity of the solute.
Problem 13
The answer is (a). This contains more moles of the substance than (b) and (c).
Problem 15
Osmosis is the process by which solvent molecules move through a semi-permeable
membrane from a lower concentration solution to a higher concentration solution.
Osmotic pressure is the pressure needed to stop osmosis.
Problem 24
(a) Mass % of solute =
%96.3%100
12.4100
12.4
