Chem 162 Ready for class? Solutions
1. Explain the difference between super saturated and over saturated solution.
2.
An aqueous solution of ethanol, C2H5OH, is 19.00% ethanol by mass and the density of solution is
1.670 g mL-1.
a)
Calculate the concentration of this solution in mass/volume %.
b) Calculate the concentration of this solution in mole fraction.
c)
Calculate the concentration of this solution in molarity.
d)
Calculate the concentration of this solution in molality.
3. The solubility of Jakium in water is approximately 0.080 M atSTP. Calculate the pressure when the
solubility is 0.0224M.
4.
At 23.0 °C, the vapor pressure of acetonitrile, CH3CN, is 81.0 torr while that of acetone, C3H6O, is
184.5 torr. A solution is made with 65.5g of acetonitrile and 75.2g of acetone.
a)
Which compound is more volatile? Briefly explain.
b)
Calculate the mole fraction of each compound.
c)
What is the vapor pressure of acetonitrile in the solution?
d)
What is the vapor pressure of acetone in the solution?
e)
What is the vapor pressure of a solution?
5.
Using only the molecular drawings, no word description, show/explain “vapor pressure lowering”.
6.
Wax is a solid mixture of hydrocarbon compounds consisting of molecules with long chains of carbon
atoms. Which solvent would you expect to be most capable of dissolving wax? Explain your choice.
7.
a.
HOH b.
b.
CH3OH
c.
CF3OH
d.
HOCH2CH2OH
e.
CH3CH2CH2CH2CH2CH2CH2CH3
(a) Draw another molecular drawing to explain vapor pressure (b) Then draw another molecular
drawing to explain vapor pressure lowering. (i.e. Use ‘circle’ to notate solvent molecules and ‘square’
to notate solute molecules.)
8.
(a) Draw phase diagram for water. Locate normal boiling point, normal freezing point.
(b) On the same diagram, show the vapor pressure lowering using dotted line. Then show the normal
boiling point of the solution and normal freezing point of the solution.
(c) On the same diagram, clearly label boiling point elevation and freezing point depression.
9.
A nonionic solute with a molecular weight of 50.0 g mol-1 is dissolved in 500 g of water and the
resulting solution has a boiling point of 101.53 °C. How many grams of solute were in the solution? Kb
= 0.51 °C m-1
10. An aqueous solution which is 12.00% sodium hydroxide by weight has a freezing point of -10.40 oC.
What is the observed value of the van’t Hoff factor, i, in this solution? Kf = 1.86 °C m-1.
11. Pure glacial acetic acid, HC2H3O2, has a freezing point of 16.62 °C. Its freezing point depression
constant is: Kf = 3.57 °C m-1. A solution was made by taking 9.755 g of an unknown substance ( i=3)
and dissolving it in 90.50 g of glacial acetic acid. The measured freezing point of the solution was
7.64 °C. Calculate the molecular weight of the unknown substance.
12. An aqueous solution made by dissolving 168 mg of an unknown compound ( a nonelectrolyte) in enough
water to make 500.0 mL of solution, develops an osmotic pressure of 5.22 torr at a temperature of
23.5 °C. What is the molecular weight of this unknown compound?
13. Arrange these aqueous solutions in order of increasing boiling points without calculating their
boiling points. Explain your logic,
a. Mg(NO3)2
0.200 m ethylene glycol, C2H6O2
0.175 m LiCl
pure water
14. What is the expected freezing point of a solution that contains 25.0 g of fructose, C6H12O6, in 250.0
g of H2O? Kf = 1.86 oC m-1.