Chemistry 1050
Gases
Fall 2010
Text: Petrucci Herring Madura Bissonette 10th Edition (Chapter 6)
Suggested text problems.
Exercises: 1, 3, 5, 9, 11,13, 15, 17, 19, 23, 25, 27, 29, 33, 35, 37, 39, 41, 45, 47, 49,
51, 53, 55, 57, 61, 65, 67, 69, 71, 73, 77, 81, 83, 97, 98, 105
Text: Petrucci Harwood Herring Madura 9 th Edition (Chapter 6)
Exercises: 1, 5, 7, 9, 11, 13, 17, 19, 23, 25, 27, 29, 33, 37, 39, 43, 45, 49, 51, 53, 59,
61, 63, 65, 71, 73, 75, 82, 86, 89, 92
1.
The liquid level in the open arm of an open!end manometer as well as the liquid level
in the arm connected to a container of gas are measured in millimeters above a
reference point. Assume barometric pressure to be 757 mmHg and the liquid to be
mercury. Calculate the pressure of the gas in the container under the following sets of
conditions.
Gas Sample A
The height of liquid mercury above the reference point on the open arm (exposed to
the atmosphere) is 28 mm and the height of liquid mercury on the gas arm is 312 mm
above the same reference point.
Gas Sample B
The height of liquid mercury above the reference point on the open arm is 198 mm and
the height of liquid mercury on the gas arm is 142 mm above the same reference point.
2.
(a)
Explain why it would be an advantage to replace the mercury in an open!end
manometer with a much lower density liquid such as liquid glycerol when the
pressure of the gas sample is close to barometric pressure.
(b)
A manometer is filled with glycerol (d = 1.26 g mLG1) instead of liquid mercury
(d = 13.5 g mLG1). The height of glycerol above a reference point on the open
arm of the manometer is 179 mm and the height of glycerol in the gas arm is
136 mm above the same reference point. Calculate the pressure of the gas
in the container in kilopascals if the barometric pressure is 102.39 kPa. Hint:
convert the liquid pressure due to the difference in glycerol levels first to the
equivalent liquid pressure in mm Hg.
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3.
4.
The volume of a sample of gas is reduced from 4.00 L to 1.60 L. If the initial pressure
is 100.0 kPa and the temperature remains constant at 20°C, what is the new pressure?
The temperature of a sample of gas in a flexible 5.00 L container is "tripled" from 21°C
to 63°C. If the pressure is maintained constant, what is the new volume?
5.
A sample of argon gas in a 4.00 L container at 23°C has a mass of 15.98 g. A sample
of an unknown gas in the same container at 23°C and at the same pressure has a
mass of 8.07 g. What is the molar mass of the unknown gas?
6.
A mixture consisting of 8.00 g each of N2, O2 and H2 is introduced into an evacuated
flask with a volume of 150 L at 50°C.
(a)
Find the mole fraction of each gas.
(b)
What is the total pressure of the gas mixture?
(c)
What is the partial pressure of N2.
(d)
How many grams of CO2 must be added to double the pressure?
7.
A sample of helium gas in a 25.0 L container at 212°C has a pressure of 148 kPa.
The container volume is reduced to 5.00 L to compress the gas. If the new pressure
of the gas is 168 kPa, what is the new temperature of the gas in °C?
8.
A sample of gas containing carbon, hydrogen and oxygen having a mass of 0.3001 g,
occupies a volume of 150.1 mL at 70.0°C and a measured pressure of 95.0 kPa. If
the sample of gas undergoes complete combustion in oxygen, 0.4399 g CO2 and
0.1801 g H2O are produced. What is the molecular formula of the gas?
9.
What volume of hydrogen gas measured at STP would be produced by the reaction
of 4.00 g of sodium with water?
2 Na(s) + 2 H2O(l) → H2(g) + 2 NaOH(aq)
10.
TNT, trinitrotoluene, decomposes according to the following chemical equation:
2 C 7H5N3O6(s) → 12 CO(g) + 2 C(s) + 5 H2(g) + 3 N2(g)
If 112 g of TNT decomposes completely in an evacuated 5.00 L container at 500°C,
what will be the total pressure exerted by the gaseous products in kPa?
11.
Potassium chlorate decomposes to form O2 gas according to the following equation:
2
2 KCIO 3(s) → 2 KCI(s) + 3 O2(g)
If 8.84 L of O2 gas are produced at a pressure of 82.67 kPa at 20°C, how many grams
of KCIO 3 decomposed?
12.
Perchloric acid can be produced by dissolving Cl2O7(g) in water. How many liters of
Cl2O7(g) measured at 20°C and 103 kPa, are required to make 25.0 L of 6.00 molALG1
HClO4(aq)?
Cl2O7(g) + H2O(l) → 2 HClO4(aq)
13.
Nitrogen trichloride gas decomposes according to the following equation:
2 NCl3(g) → 3 Cl2(g) + N2(g)
If 30.0 L of NCl3(g) measured at 25°C and 102 kPa decompose completely to
products measured at the same temperature and pressure, what is the total volume of
gaseous products?
14.
H2 gas can be prepared in a laboratory by adding aluminum metal to a strong acid:
e.g. 2 Al(s) + 6 HNO3(aq) → 2 Al(NO3)3(aq) (aq) + 3 H2(g)
In an experiment, 191.2 mL of H2 is collected by downward displacement of water in
an inverted measuring cylinder at 24°C from the reaction of 0.1501 g Al with 44.5 mL
of 0.500 M HNO3(aq). Atmospheric pressure was measured with a barometer and
found to be 752.6 mmHg.
(a)
What is the partial pressure of the H2 collected? The vapor pressure of water
at 24°C is 22.4 mmHg.
(b)
Calculate the % yield of H2(g).
(c)
What volume of dry H2 would have been collected at 24°C and one standard
atmosphere of pressure?
15. A compound containing only carbon and hydrogen is 85.62% carbon by mass. A 1.223
g sample of this compound occupies a volume of 658 mL at 32°C and a pressure of 112
kPa. What is the molecular formula of the compound?
16. Find the density of Cl2(g) (a) at 12°C and 3.474 bar, and
(b) at STP
17. A mixture of argon and chlorine gas is 25.6% Argon by volume. What is the partial
pressure of argon in the mixture if the total pressure is 126 kPa?
18. A mixture of argon and chlorine gas is 25.6% Argon by mass. What is the partial
pressure of argon in the mixture if the total pressure is 126 kPa?
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19. The oxygen gas produced from the complete decomposition of a sample of silver oxide
was collected in a 2.50 L flask over water at 28°C. The total pressure of gas in the flask
was 0.9643 atm, The vapour pressure of water at 28°C is 3.77 kPa.
(a)
(b)
What is the partial pressure of O2 in the flask?
How many grams of Ag2O were present in the sample which had decomposed?
2 Ag2O(s) → 4 Ag(s)+ O2(g)
20. Gaseous iodine pentafluoride, IF5, can be prepared by the reaction of solid iodine and
gaseous fluorine:
I2(s) + 5 F 2(g) → 2 IF5(g)
A 5.00 L flask is charged with 10.0 g I2 and 10.0 g F 2, and the reaction proceeds until
one of the reactants is totally consumed. After reaction is complete, the temperature of
the flask is 125°C.
(a)
(b)
Calculate the partial pressure of IF5(g) in the flask.
Calculate the mole fraction of IF5(g) in the flask.
21. A sample of neon in a rigid container at 23 °C has a measured pressure of 48.3 kPa.
Calculate the new pressure of the gas if the temperature is lowered to -23°C.
22. A mixture of helium and neon gases is collected over water at 28.0°C and a total
pressure of 745 mmHg. The vapor pressure of water at 28°C is 28.3 mmHg.
(a)
(b)
If the partial pressure of helium is 368 mmHg, what is the partial pressure of
neon?
Calculate the mole fraction of helium in the mixture of collected gas.
23. A 2.00 L bulb containing nitrogen at a pressure of 650 mmHg is connected to a 5.00 L
bulb containing hydrogen at a pressure of 450 mmHg through a stopcock in the closed
position. Calculate the total pressure of gas in the system after the stopcock is turned
to the open position and the two gases allowed to mix. Assume the temperature
remains constant.
24. A 35.0 L gas tank filled with argon at a pressure of 4.80 atm is connected by a valve to
a second gas tank of unknown volume containing neon at a pressure of 7.60 atm. When
the value is opened and the gases allowed to mix, the total pressure measured is 5.64
atm. Calculate the volume of the second gas tank assuming the temperature remains
constant.
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25. A certain hydrate has the formula MgSO4AXH2O. A quantity of 7.76 g of the compound
is heated in an oven to drive off the water. If the steam generated exerts a pressure of
3.55 atm in a 2.00 L container at 120°C, calculate X in the formula of the hydrate.
26. When 5.42 g of NaBH4 are allowed to react with 5.00 L of BF3 gas measured at STP,
1.72 L of B2H6 gas are collected measured at 107 kPa and 37°C. Calculate the
percentage yield of B2H6 . The balanced reaction between NaBH4 and BF3 is
described by the equation given below:
3 NaBH4(s)+ 4 BF3(g) → 2 B 2H6(g) + 3 NaBF4(s)
27. A 3.00 g sample of impure calcium carbonate (contaminated with calcium chloride) was
completely dissolved in hydrochloric acid liberating 0.606 L of carbon dioxide measured
at 14.0°C and 792 torr. Calculate the percent by mass (percent purity) of calcium
carbonate in the sample.
CaCO3(s) + 2 HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)
28.
A compound of P and F was analysed as follows: Heating 0.2324 g of the compound
in a 378 mL container turned all of it to gas, which had a pressure of 12.97 kPa at 77°C.
Then the same gas sample was dissolved in excess calcium chloride solution,
converting all of the F to 0.2631 g of CaF 2 precipitate. Determine the molecular
formula of the compound.
29. A mixture of hydrogen and oxygen is prepared by electrolysing 1.32 g of water, and the
mixture of gases collected over water at 30°C at a total pressure of 748 mmHg. The
volume of "wet " gas obtained is 2.90 L. Calculate the vapor pressure of water at 30°C
from these data.
Electrolysis Reaction: 2 H2O(l) → 2 H2(g) + O2(g)
30.
A mixture contains nitrogen gas at a partial pressure of 0.675 atm and sulfur
hexafluoride gas at a partial pressure of 0.250 atm.
(a)
Calculate the mole fraction of each gas in the mixture.
(b)
If the mixture occupies a volume of 5.00 L at 35.0 °C, calculate the total number
of moles of gas and the mass of each gas present.
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31.
Consider a sample of helium in a 10.0 L container at 100 K.
(a)
(b)
(c)
32.
33.
34.
35.
If the helium is compressed to a volume of 5.00 L at 100 K, what is the effect
on the average translational kinetic energy and root-mean-square velocity of the
helium atoms?
If the gas is changed to oxygen, by what factor does the average translational
kinetic energy and the root-mean-square velocity change?
If the temperature is increased from 100 K to 400 K, what is the effect on the
average translational kinetic energy and root-mean-square velocity of the
helium atoms?
In the van der Waals equation (equation 6.26 in your text), what is the significance of the
correction terms, nb and n2 a/V 2?
Calculate the root-mean-square velocity of CH4 molecules in a sample of CH4 gas at
273 °C.
Nickel forms a gaseous compound Ni(CO)X. Determine the value of X given the fact
that under the same conditions of temperature and pressure, methane CH4 diffuses 3.30
times faster than the compound Ni(CO)X.
At a given temperature and pressure, it takes 4.85 minutes for 1.50 L of argon to effuse
through a membrane. How long will it take for 1.50 L of helium or SF6 to effuse?
Answers:
1.
2.
P gas A = 473 mmHg, P gas B = 815 mmHg
P gas B = 102.94 kPa
The advantage of the much lower density liquid would be a much larger difference in
the height of the liquid in the two arms which can be measured with a smaller relative
error. This would allow a more accurate determination of the gas pressure.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
P(new) = 250 kPa
V(new) = 5.71 L
molar mass (unknown gas) = 20.2 g molG1
(a)
(b)
(c)
X(N2) = 0.0635, X(O2) = 0.0555, X(H2) = 0.881
total pressure = 80.6 kPa
P(N2) = 5.12 kPa
(d)
198 g CO2
T = -163°C
molecular formula = C 2H4O2
V(H2) = 1.95 L
Total Pressure = 6.34 X 103 kPa
13.
24.5 g KCIO 3
V(Cl2O7) = 1.77 x 103 L
V(total) = 60.0 L
14.
(a)
P(H2)= 730.2 mmHg
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15.
16.
17.
18.
(b)
% yield = 90.3 %
(c)
V(H2)= 183.7 mL
molecular formula is C 3H6
(a)
d = 10.5 g LG1
(b)
d(STP) = 3.16 g LG1
P(Ar) = 32.3 kPa
19.
P(Ar) = 48.9 kPa
(a)
P(O2) = 93.91 kPa
(b)
mass(Ag2O) = 43.5 g
20.
(a)
P(IF5) = 0.515 atm
(b)
X(IF5) = 0.544
21.
22.
23.
23.
25.
26.
P(Ne) = 40.8 kPa
(a)
P(He) = 349 mmHg
(b)
0.494
Total pressure = 507 mmHg
V = 15.0 L
MgSO4A7H2O, i.e. X = 7
27.
% yield of B 2H6 = 74.8 %
89.4 % CaCO3
28.
29.
molecular formula is P 2F4
P(H2O) = 32 mmHg
30.
(a) xN2 = 0.730 xSF6 = 0.270
31
(b) 0.183 moles of gas, 3.74 g N2 and 7.22 g SF6
(a)
no effect on either.
(b)
(c)
the average translational kinetic energy does not change but the root-meansquare velocity decreases by the square root of 8.
the average translational kinetic energy increases by a factor of 4 and the rootmean-square velocity increased by a factor of the square root of 4, i.e. a factor
32.
of 2.
nb is the excluded volume for n moles of gas.
33.
n2a/V 2 corrects the real(measured) pressure for intermolecular forces of attraction.
921 m sG1.
34.
35.
X=4
t(He) = 1.54 min
t (SF6) = 9.27 min
Developed by Dr. Chris Flinn
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