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CHEM 101: PRACTICE MIDTERM I
Note: This exam is intended for you to use as a study tool. Do not study solely off this practice midterm. Read
your class notes and textbook, make sure you understand the problem sets, and attend SI sessions and/or Nucleus
tutoring hours if you can.
PART 1) MULTIPLE CHOICE
Please indicate, by circling the letter next to the answer, the most appropriate answer to each of
the following questions.
1) Which is NOT a postulate of the Kinetic Molecular Theory of Gases?
a) A gas is composed of many extremely small particles travelling in straight lines.
b) Molecules collide only fleetingly with one another and with the walls of their containers.
c) There are assumed to be forces between molecules during the very brief moments of collision.
d) Molecules and atoms are separated by distances many times greater than their radii.
2) Arrange in order by decreasing boiling point:
CH3CH2OH, HOCH2CH2OH, C4H10
a) HOCH2CH2OH, CH3CH2OH, C4H10
b) C4H10, HOCH2CH2OH, CH3CH2OH
c) HOCH2CH2OH, C4H10, CH3CH2OH
d) C4H10, CH3CH2OH, HOCH2CH2OH
e) CH3CH2OH, C4H10, HOCH2CH2OH
3) Liquid and vapour phases become indistinguishable at the:
a) triple point
b) normal point
c) absolute point
d) critical point
4) Molecules A and B have relative effusion rates of 6:3. What is the ratio of their molar masses?
a) 6:3
b) 36:9
c) 3:6
d) 9:36
5) The mass percent of an aqueous solution containing 1.0 g ephedrine in 20.0 mL solution is said to
be:
a) 5.0 % ephedrine
b) 1.0 % ephedrine
c) 0.50 % ephedrine
d) 0.050 % ephedrine
e) 20.0 % ephedrine
6) 3.84 g of H2CO3 is dissolved in 524 mL of water. What is the molarity of the carbonate in solution?
a) 27.1 M
b) 0.437 M
c) 0.118 M
d) 0.003 M
7) What is the mass percent of carbon in octane, C8H18?
a) 30.77 %
b) 84.12 %
c) 96.09 %
d) 114.1 %
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8) The mass percent of concentrated HClO4 (aq) (MW = 100.46 g/mol) is 70.46%, and its density is 1.67
g/mL. What is the molarity of concentrated HClO4 (aq)?
a) 4.20 M
b) 7.18 M
c) 11.7 M
d) 14.2 M
9) A 1.00 m solution of NaCl in water contains:
a) 1.00 mol NaCl per 1000.0 kg H2O
b) 1.00 mol NaCl per 1000.0 g H2O
c) 1.00 mol NaCl per 1000.0 mol H2O
d) 1000.0 g NaCl per 1000.0 g H2O
e) 1.00 g NaCl per 1000.0 g H2O
10) Solutions are made that contain 0.1 moles of each of the following compounds in 100 g of H2O.
Choose the compound whose solution will have the lowest freezing point.
a) NaBr
b) KClO3
c) MgSO4
d) MgCl2
e) CO2
f) H2O
11) Which of the following is not a colligative property?
a) freezing point depression
b) boiling point elevation
c) osmotic pressure
d) solubility
e) none of the above
12) According to the phase diagram below, which of the following statements is wrong?
a) at the temperature and pressure of point 1, substance W exists as a three-phase equilibrium system
b) at the temperature of point 2, a pressure of 500 torr is sufficient to liquefy gaseous W
c) if the W (l) = W (g) system is maintained at the temperature of point 3 while pressure is decreased,
more W will vaporize
d) if liquid W is maintained at the pressure of point 4 while the temperature is increased to 80 °C, the
liquid will vapourize
e) the existence of liquid W at -40°C and 500 torr represents the metastable condition of
“supercooling”
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13) When the vapour pressure of a liquid equals atmospheric pressure, the temperature of the liquid
equals:
a) 100°C
b) the normal boiling point
c) the standard boiling point
d) the boiling point
e) none of these
14) What is the freezing point of a solution containing 3.10 g of benzene (MW=78.11 g/mol) dissolved
in 32.0 g of p-dichlorobenzene (MW=147.0 g/mol), given that the freezing point of p-dichlorobenzene
is 53.0°C and Kf = 7.10 K/m?
a) 44.2°C
b) 51.8 °C
c) 54.2 °C
d) 61.8 °C
15) Henry’s Law constants for aqueous solutions at 25°C are 8.20 x 10-7 molal/mmHg for N2 and 1.62
x 10-6 molal/mmHg for O2. Determine the solubility of oxygen in water under an atmospheric pressure
of 760 mmHg, assuming that air is 80% N2 and 20% O2.
a) 6.16 x 10-3 m
b) 2.46 x 10-4 m
c) 1.25 x 10-4 m
d) 4.99 x 10-4 m
e) 1.23 x 10-3 m
16) The vapour pressure of pure hexane and pure heptane at 25°C are 151.4 mmHg and 45.62 mmHg,
respectively. A solution contains 0.800 mol fraction n-hexane and 0.200 mol fraction n-heptane. What
is the composition of the vapour in equilibrium with this solution at 25°C?
a) 80.0% hexane, 20 % heptane
b) 50 % hexane, 50 % heptanes
c) 77.0 % hexane, 23.0 % heptane
d) 45.0 % hexane, 55.0 % heptane
e) 93.0 % hexane, 7.0 % heptanes
17) A solution of nonvolatile solute has an osmotic pressure of 141 mmHg at 25°C. What is the
molarity of the solution?
a) 0.00759 M
b) 5.76 M
c) 0.0904 M
d) 0.0339 M
e) 0.174 M
18) At a temperature of 20°C and a pressure of 1 bar, a gas has a density of 2.50 g/L. What is the molar
mass of the gas?
a) 54.9 g/mol
b) 59.1 g/mol
c) 64.0 g/mol
d) 5560 g/mol
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PART 2) NUMERICAL CALCULATIONS
1) Answer either (a) or (b) for the following:
a) If the density of gasoline is 0.794 g/mL, what volume of carbon dioxide is generated by the
combustion of 1.0 litres of gasoline, assuming that the gas is at room temperature (22°C, 1 atm)?
(Assume the following equation: 2C8H18 + 2SO2  16CO2 + 9H2O)
b) Using a “time of flight” apparatus, if a gas molecule takes a mean value of 0.012 seconds to travel
2.26 metres, what is the molecular weight of the gas, assuming STP?
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2) Answer either (a) or (b) for the following:
a) A sample of an unknown compound weighing 6.42 g, when dissolved in 80.00 g H2O, lowers the
freezing point by 0.700 °C. What is the molecular weight of the compound? (Kf for water = 1.86
°C/m).
b) How many grams of sodium chloride (MW=58.4428 g/mol) would be required to raise the
temperature of 1.0 litre of water by 1.0°C (Kb=0.512°C/m)?
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3) Answer either (a) or (b) for the following:
a) An aqueous solution containing 12.0% MgCl2 by mass has a density of 1.105 g/mL. What is the
mole fraction of water in this solution?
b) If a solution containing 3 moles of A and 7 moles of B boils at 85°C and the vapour pressure of pure
A at 85°C is 400 mmHg, what is the vapour pressure of pure B at this temperature?
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4) Answer either (a) or (b) for the following:
a) What are the equilibrium concentrations of H2, Cl2, and HCl if Kp = 110 and [H2]o=0.541 atm,
[Cl2]o=0.368 atm, and [HCl]o = 0.612 atm?
H2 + Cl2 ⇌ 2HCl
b) Given the following reactions and equilibrium constants:
N2 (g) + ½ O2 (g) ⇌ N2O (g)
Keq = 2.7 x 10-18
N2 (g) + O2 (g) ⇌ 2NO (g)
Keq = 4.7 x 10-31
What is the equilibrium constant for the following reaction?
N2O (g) + ½ O2 (g) ⇌ 2NO (g)
-END OF EXAM-
Keq = ?