1.
Pure cyclohexane has a freezing point of 6.55 oC. When a
0.358 g sample of a non-volatile, non-ionizing solute was
dissolved in 20.00 g of cyclohexane, the resulting solution
had a freezing point of 3.27 oC. The freezing point
depression constant (Kf) for cyclohexane is 20.0 oC/m. What
is the molecular weight of the unknown solute?
a) 74.2 g/mol
b) 89.6 g/mol
d) 171 g/mol
e) 216 g/mol
c) 109 g/mol
2. A 2.45 g sample of a protein having a molecular weight of
22830 g/mol was dissolved in enough water to produce a
solution having a volume of 114 mL. What is the osmotic
pressure of this solution at 25.0 oC?
(Note: R = 0.0820584 L atm / K mol and 1 atm = 760 torr)
a) 1.83 torr
b) 5.21 torr
d) 17.5 torr
e) 27.4 torr
c) 10.8 torr
3. A 3.31 g sample of a protein was dissolved in enough water
to produce a solution having a volume of 215 mL. At 25 oC,
the osmotic pressure of this solution was 12.4 torr. What
is the molecular weight of the protein?
(Note: R = 0.0820584 L atm / K mol and 1 atm = 760 torr)
a) 1.05 x 104 g/mol
b) 2.31 x 104 g/mol
c) 4.85 x 104 g/mol
d) 8.67 x 104 g/mol
e) 3.74 x 105 g/mol
4. An aqueous solution of glycerol (CH2OHCHOHCH2OH or written
in more compact form, C3H8O3) was made by dissolving 50.00 g
of glycerol in 50.00 g of water. In this solution,
glycerol acts as a non-volatile solute, while water is a
volatile solvent. At 25.0 oC, the vapor pressure of pure
water is 23.8 torr. What is the vapor pressure of this
solution at 25.0 oC?
a) 4.8 torr
b) 7.5 torr
d) 15.6 torr
e) 19.9 torr
c) 12.1 torr
5. What vapor pressure lowering is caused by the presence of
glycerol in the previous problem?
a) 3.9 torr
b) 8.2 torr
d) 16.3 torr
e) 19.0 torr
c) 11.7 torr
6. Toluene (C7H8) and benzene (C6H6) are both volatile.
At 25 oC, pure C7H8 has a vapor pressure of 28.4 torr and
pure C6H6 has a vapor pressure of 95.1 torr. If a solution
is made by dissolving 50.00 g of C7H8 in 50.00 g of C6H6,
what will be the vapor pressure of the solution at 25 oC?
(Hint: Since both substances are volatile, you must
calculate the pressure of each and then add them together
to get the total vapor pressure of the solution.)
a) 22.9 torr
b) 44.1 torr
d) 85.1 torr
e) 107.3 torr
c) 64.5 torr