Chemistry
§ 06.PQ1
Gases – Practice Quiz - 1
1. A device that is used to measure air pressure (2 correct)
a. hydrometer
b. barometer
c. picometer
d. manometer
e. sphygmomanometer
2. What is the pressure of the gas inside the reservoir if the atmospheric pressure is 773 mmHg
and the height of the mercury column is 22 mmHg?
a. 1.05 atm
b. 100 kPa
c. 782 torr
d. 15.1 psi
3. Pressure and temperature of a gas are:
a. inversely proportional
4.
b. directly proportional
Two sealed 2.0-L flasks contain the same number of moles of the same gas. Flask 1 has a
temperature of 303 K. Flask 2 has a temperature of 606 K. Which of the following
statements is true?
a. Flask 1 has the same pressure as flask 2.
b. Flask 2 has twice the pressure as flask 1.
c. Flask 1 has twice the pressure of flask 2.
5. A hydrocarbon gas with the empirical formula CH2 has a density of 1.3 g/L at 0oC and 1.00
atm. Which of the following is a possible molecular formula for this compound?
a. CH2
b. C2H4
c. C3H6
d. C4H8
e. C5H10
6. A sample of gas has a constant pressure of 1.20 atm @ 22.0oC, and a volume of 0.570 L.
What would the volume be at 52.0oC?
7. Two samples of the same gas are in two separate containers at 1.20 atm and 55.0oC. The first
container has 0.0535 mol of the gas and a volume of 1.20 L. Container 2 has a volume of 3.60
L. How many moles of the gas does it contain?
8. In the Haber process, ammonia (NH3) gas is formed from hydrogen and nitrogen gases. If
0.4 mol of nitrogen gas is combined with 1.2 mol of hydrogen (total volume is 2.20 L), what
is the volume of ammonia gas produced? (assume constant temperature & pressure)
F:\2014-2015\340_Masterton\340_tests_and_quizzes\340.05.Gases\340.04.Gases.PQ04.01_KEY.docx (9/29/2014)
Chemistry
Gases – Practice Quiz
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9. Two 2.0 L flasks are at the same temperature and pressure. Flask A contains oxygen gas ad
flask B contains sulfur trioxide. Which flask contains the greater number of molecules?
10. Consider two gases. Bulb A has a volume of 6.0 L and a pressure of 1.2 atm. It is joined to
bulb B that has a volume of 12.0 L and a pressure of 2.4 atm. If the valve is opened allowing
the air volumes to mix, what will be the resulting pressure in the connected tanks?
11. Which of the following gases had the highest density (assume the same container): CO, CO2,
SO2, O3, all have the same density?
12. A sample of methane (CH4) gas having a volume of 2.80 L at 25oC and 1.65 atm is mixed
with O2 gas having a volume of 35.0 L at 31oC and 1.25 atm. The mixture is then ignited to
form CO2 and H2O at a final temperature of 125oC and pressure of 2.50 atm. Calculate the
volume of the CO2.
13. A sample of solid potassium chlorate (KClO3) was heated in a test
tube and decomposed:
2KClO3(s)  2KCl(s) + 3O2(g)
The oxygen was collected by displacement of water at 22oC. The
volume of the gas was 0.650 L and the vapor pressure of water at
22oC is 21 torr. Atmospheric pressure is 754 torr. Calculate the partial pressure of the
oxygen gas and the mass of KClO3 in the sample that was decomposed.
14. Calculate the ratio of the effusion rates of hydrogen gas (H2) and uranium hexafluoride
(UF6, a gas used in the enrichment process to produce fuel for nuclear reactors.
15. Hydrochloric (HCl) and ammonia (NH3) gases are released at either ends of a glass tube.
At which point inside the tube would they meet?
16. What are the diatomic gas molecules at room temperature?
17. Under what conditions would a real gas deviate from expected ideal gas and what is(are)
the mechanism(s)?
Chemistry
Gases – Practice Quiz
p. 3
Answers
1.
b & d. barometer & manometer
2.
a. mercury column higher than reservoir
= pressure inside > pressure outside
= 773 (outside) + 22 (height) = 795 mmHg /760 mm Hg = 105
3.
b. If pressure is increased, temperature will also go up (combined gas law)
4.
b. Pressure and temperature are directly related. Doubling the temperature would result
in doubling the pressure.
5.
In this problem, we need a molar mass to determine the molecular formula. Notice that
the conditions in the problem, 0oC and 1 atm are STP conditions, and this allows us to use
, which means you have to do a rough estimate.
6.
7.
8.
Estimate 22.4L ≈ 20 L and of 20 ≈ 7. Thus
of 20 is 20+7=27.
Of the options given, the only formula with a molar mass of ~29 is (b), C2H4 with a molar
mass of 28.
combined gas law. P and n are the same => V2 = (V1 * T2)/T1
V2 = (0.570 L * 325)/ 295 K = 0.628 L
can think of this a two different gases. same pressure & temp: n2 = (V2 * n1)/V1
n2 = (3.60 L * 0.0535 mol)/(1.20 L) = 0.161 mol
Balanced Chemical Equation: 1N2 + 3H2 -> 2NH3
Limiting Reactant? N2:
H2:
9.
10.
11.
= 0.8 mol
= 0.8 mol so we don’t have to consider any residual reactants
Combined gas law: V1/n1 = V2/n2
initial moles = 0.4 + 1.2 = 1.6 mol; final moles (assuming complete reaction) = 0.8 mol
Because the number of moles decreases by half, so should the volume (directly
proportional). = 1.10 L
Neither. Temp, pressure & volume are all the same. Thus, the only other factor is the
number of moles. From Avogadro’s law. Example: any gas at STP occupies 22.4 L.
Vol A increased by 3 (6 -> 18), so partial pressure of A is reduced by 3: 1.2/3 = 0.4atm
Vol. B increased by 1.5 (12->18), so it’s partial pressure is reduced by 1.5: 2.4/1.5=1.6atm
Total pressure is 0.4 atm + 1.6 atm = 2.0 atm
Density = mass / volume. B/c they’re in the same container, the volumes are the same.
The heaviest is SO2 (~64g/mol), so it is the densest.
Chemistry
12.
Gases – Practice Quiz
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Step-1: Balanced chemical equation:
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
Step-2: Limiting reactant & number of moles CO2 formed:
CH4:
(
)(
)
)(
(
(
O2:
)(
(
Step-3: Volume of CO2:
(
PV = nRT
)
)(
)

)(
)(
(
13.
)
)
)
A. What is the partial pressure of the O2? PTOTAL = PO2 + PH2O  PO2= 733 torr
B. Number of moles O2: n = PV/RT  nO2 = 2.587 x 10–2 mol
C. Amount KClO3:
14.
13.2 (rH2/rUF6)=(352.02/2.015) = 13.2. The effusion rate of H2 is about 13 times greater
than UF6.
15.
16.
17.
H2 N2 O2 Cl2 Br2 I2 F2
Low temperature & high pressures. These conditions allow the molecules to interact
more and therefore reducing the amount of completely elastic collisions. Also, as the
pressure increases, the relative volume of the particles, themselves, becomes significant
compared to the free space allowed for the molecules to have translational energy.