Quiz 2, SC112
Name: ____________Key__________________
1. (3 pts) Circle all of the true statements about aqueous solutions (True statements are in bold italics.)
a. The solubility of all gases decreases as the temperature increases. (Increasing the temperature
favors the more disordered state which is the undissolved gas.)
b. The solubility of all solids increases as the temperature increases. (The solubility of some solids
decreases with increasing temperature because the more disordered state is sometimes the undissolved solid.)
c. The solubility of liquids and solids in water is largely unaffected by pressure. (This is because
solids and liquids are essentially uncompressible so their concentrations are not affected by
pressure.)
d. The solubility of a gas decreases as the partial pressure of the gas increases. (The opposite is true
because a larger partial pressure means a larger concentration of gas and a higher rate of
dissolving.)
e. Usually, a polar solute is more soluble in a polar solvent than in a non-polar solvent. (Like
dissolves like.)
f. No solid is miscible with water. (To be miscible, solute-solute and solvent-solvent interactions
must be very similar in both type and magnitude. The intermolecular forces between
molecules/ions in a solid are significantly stronger than those in a liquid.)
2. Explain the following. Keep your answers as brief as possible.
There is also an entropy argument. Compare the evaporation of pure water to the evaporation of
water from a solution:
H2O(l) → H2O(g)
H2O(solution) → H2O(g)
When pure water evaporates there is a larger increase in entropy than when water evaporates from a
solution. This is because the entropy of an aqueous solution is larger than the entropy of pure water.
So there is a greater driving force for evaporation of pure water. Thus, when the two systems reach
equilibrium, there is more water vapor in the system with pure water.
3.
(5 pts) Calculate the boiling point of a solution that is made by dissolving 328 g of sodium phosphate
(Na3PO4; mw = 164 g/mol) in 500.0 g of water. Assume an ideal van’t Hoff factor. Show your work.
Sig. figs count.
4. (5 pts) Calculate the molar mass of a molecular compound based on the following data.
5.00 g of the compound was dissolved in water.
Water was added until the total volume was 100.0 mL.
The osmotic pressure of the resulting solution was found to be 6.00 atm (at 25oC)
Chapter 12 Equations
c = kP (Henry’s Law)
Colligative Properties
P1 = X1P1o (Raoult’s law)
Tf = Kfmi
Kf for water = 1.86oC/m
Tb = Kbmi
Kb for water = 0.510oC/m
V = nRT or  = MRT
R = 0.0821 L-atm/mol-K