CHEM 1523: Principles of Chemistry A1-1
Assignment 1 (8%)
Total marks: 100 (equal marks for each question)
1. a. The natural gas in a storage reservoir, under a pressure of 1.00
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atmosphere, has a volume of 2.74 × 10 L at 20.0°C. The temperature at a
later date falls to –20.0°C, but the pressure remains constant. Calculate
the volume that the gas now occupies. (5 marks)
b. To what pressure must 0.400 L of gas at an initial pressure of 700 torr be
changed to reduce the volume to 0.300 L? Assume no change in
temperature or mass of the gas. (5 marks)
2. How many litres would 1.00 g of nitrogen gas (N2) occupy at:
a. STP? (5 marks)
b. 84.0°C and 2.15 atm? (5 marks)
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3. An unknown gas has a density of 1.34 g L at STP. What is the molar mass of
the gas? (10 marks)
4. How many grams of solid KClO3 are needed to prepare 18.0 L of oxygen, O2,
that is collected over water at 1.00 atm pressure and at a temperature of 22°C?
The vapour pressure of water at 22°C is 19.8 torr. The reaction is
2KClO3(s) 2KCl(s) + 3O2(g)
(10 marks)
5. Air is 21.0% by volume oxygen molecules, and C3H8 produces CO2 and H2O
on combustion. What volume of air at 1.01 atm and 20.0°C would be required
to burn 38.8 kg of propane (C3H8)? (10 marks)
6. a. Use the ideal gas law to calculate the temperature at which it would be
possible to contain 3.00 moles of O2 in a 2.00 L vessel under a pressure of
20.0 atm. (4 marks)
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A1-2 Assignment 1
b. Use the van der Waals equation to calculate the temperature for the same
conditions as in part (a), and hence calculate the per cent deviation from
ideality. (6 marks)
7. a. Distinguish between the terms isotope and allotrope. Give appropriate
examples. (2 marks)
b. Hydrogen has two naturally occurring isotopes: normal hydrogen (H),
with atomic mass of 1, and deuterium (D), with atomic mass of 2. A
mixture containing an equal number of moles of H2 and D2 is allowed to
effuse down a capillary. What per cent of the molecules effusing first
would be D2? (4 marks)
c. The two gaseous forms of elemental oxygen are O2 and O3. A mixture
containing equal quantities of O2 and O3 is allowed to effuse down a
capillary. What per cent of the molecules effusing first would be O3?
(4 marks)
8. At STP, air can be considered a mixture of ideal gases: 21.0% O2, 78.0% N2,
and 1.00% Ar by volume.
a. Calculate the partial pressure of each gas at STP. (2 marks)
b. Briefly explain Dalton’s law of partial pressures, using the kinetic theory
of gases. (4 marks)
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c. Calculate the density of air in g L at STP. (4 marks)
9. Two containers of the same volume are evacuated. Container 1 is maintained
at a temperature of 400 K and filled with oxygen gas to a pressure of 750 mm
Hg. Container 2 is maintained at a temperature of 200 K and filled with
hydrogen gas to a pressure of 750 mm Hg. Compare the two samples of gas
quantitatively with regard to: (2.5 marks each)
a. Number of molecules
b. Mass
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CHEM 1523: Principles of Chemistry A1-3
c. Average molecular kinetic energy
d. Average molecular speed (rms)
10. Heliox is a helium-oxygen mixture used in scuba diving. At 298K in a 16.0 L
tank, the partial pressures of helium and oxygen are 18.5 atm and 0.413 atm,
respectively.
a. Calculate the total pressure of the gas mixture. (2 marks)
b. Calculate the mole fractions of each component of the mixture. (3 marks)
c. Calculate the mass of each component in the mixture. (5 marks)
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