Mixtures of Gases
Understanding Concepts
1. A 1-L flask of air at SATP contains carbon dioxide with a partial pressure
of 2 kPa. If all other gases were removed from the flask and the
temperature remained the same, what would be the pressure of
carbon dioxide by itself in the flask?
2. Using Dalton’s values in Table 1, page 460,
(a) find the total pressure for the four gases listed, using both pressure
units given in the table;
(b) show that both totals are the same by converting millimetres of
mercury into kilopascals.
3. Beyond 60 m, compressed air is not used for underwater diving
because of the toxicity of oxygen at high partial pressures. Suppose a
commercial diver needs to work at a pressure of 14.0 atm using a
helium–oxygen breathing mixture (known as heliox) containing 1.1 atm
of oxygen. What is the partial pressure of helium in this mixture?
Answers
2. (a) 762 mm Hg, 101.6 kPa
3. 12.9 atm
Table 3: Vapour Pressure of
Water at Various
Temperatures
Temperature Vapour pressure
(°C) (kPa)
17.0 1.94
18.0 2.06
19.0 2.20
20.0 2.34
21.0 2.49
22.0 2.64
23.0 2.81
24.0 2.98
25.0 3.17
26.0 3.36
27.0 3.57
28.0 3.78
29.0 4.01
30.0 4.24
Sample Problem 2
In a laboratory, oxygen gas was collected by water displacement at an atmospheric
pressure of 96.8 kPa and a temperature of 22°C. Using Table 3, calculate
the partial pressure of dry oxygen.
Solution
The partial pressure of dry oxygen is 94.2 kPa.
Understanding Concepts
8. A sealed container of bottled water sits on a store shelf at a temperature
of 23°C. What is the partial pressure of water vapour in the air
space inside the container?
9. Nitrogen gas is collected at 20°C and a total ambient pressure of
98.1 kPa using the method of water displacement. What is the partial
pressure of dry nitrogen?
10. In an experiment, a student collected a 275-mL sample of hydrogen
at 92.4 kPa and 25°C using the water displacement method.
(a) What is the partial pressure of hydrogen?
(b) What volume would this hydrogen occupy at standard ambient
pressure of 100 kPa?
Answers
8. 2.81 kPa
9. 95.8 kPa
10. (a) 89.2 kPa
(b) 245 mL
Reactions of Gases
Sample Problem 1
A catalytic converter in the exhaust system of a car uses oxygen (from the air) to
convert carbon monoxide to carbon dioxide, which is released through the tailpipe.
If we assume the same temperature and pressure, what volume of oxygen is
required to react with 125 L of carbon monoxide produced during a 100-km trip?
Solution
The volume of oxygen required is 62.5 L.
Understanding Concepts
1. Gay-Lussac was the first to notice and publish evidence of simple
volume ratios of reacting gases. What important idea was necessary
to relate this observation to chemical equations?
2. State two empirical observations that led Avogadro to his theory.
3. If 5.00 L of propane is burned in a gas barbecue, what volume of
oxygen, at the same temperature and pressure, is required for complete
combustion?
4. In modern automobile catalytic converters, nitrogen monoxide (a pollutant)
reacts with hydrogen to produce nitrogen and water vapour (part
of the exhaust). The catalytic converter of a car meeting current emission
standards removes about 1.2 L of nitrogen monoxide at SATP for
every kilometre of driving. What volume of nitrogen gas is formed from
1.2 L of nitrogen monoxide at the same temperature and pressure?
5. The production of sulfuric acid is a very important chemical industry
in any developing or developed country (Figure 3). The main reactant
required to produce sulfuric acid is sulfur, which can be obtained
from a variety of sources.
(a) One technology for removing hydrogen sulfide from sour natural
gas involves converting part of the hydrogen sulfide to sulfur
dioxide, which then reacts with the remaining hydrogen sulfide
as shown in the reaction equation below. Predict the volume of
sulfur dioxide needed to react completely with 248 kL of
hydrogen sulfide. The gases are measured at 350°C and 250 kPa.
16 H2S(g) _ 8 SO2(g) → 3 S8(s) _ 16 H2O(g)
(b) Solid sulfur is the starting material in the typical manufacture of
sulfuric acid. First it is burned to form sulfur dioxide. Predict the
volume of oxygen required to produce 250 kL of sulfur dioxide
with all gases at 450°C and 200 kPa.
(c) In the presence of the catalyst V2O5(s), sulfur dioxide—from the
burning of sulfur or directly from the output of a smelter—reacts
with oxygen to form sulfur trioxide.
2 SO2(g) _ O2(g) → 2 SO3(g)
Predict the volumes of sulfur dioxide and oxygen needed to produce
325 kL of sulfur trioxide when all gases are measured at thesame temperature and pressure.
Answers
3. 25.0 L
4. 0.60 L
5. (a) 124 kL
(b) 250 kL (c) 325 kL SO2(g), 163 kL O2(g)
Sample Problem 2
What volume is occupied by 0.024 mol of carbon dioxide gas at SATP?
Solution
The carbon dioxide gas occupies the volume 0.60 L.
Understanding Concepts
7. Sulfur dioxide gas is emitted from marshes, volcanoes, and refineries
that process crude oil and natural gas. What amount in moles of
sulfur dioxide is contained in 50 mL of the gas at SATP?
8. Neon gas under low pressure emits the red light that glows in advertising
signs (Figure 6).
(a) What volume does 2.25 mol of neon gas occupy at STP before
being added to neon tubes in a sign?
(b) What pressure is reached when the gas is heated to 35°C by the
Sun?
(c) When designing the tube for this application, what specifications
for the quality of the tube are necessary? Provide your reasoning.
9. One gram of baking powder produces about 0.13 g of carbon dioxide.
What volume is occupied by 0.13 g of carbon dioxide gas at SATP?
10. Volatile liquids vaporize rapidly from opened containers or if spilled.
Some vapours, such as those from gasoline, contribute to the formation
of smog. What volume at STP is occupied by gasoline vapours
from 50.0 g of spilled gasoline (assume octane, C8H18(l))?
11. Millions of tonnes of nitrogen dioxide are dumped into the atmosphere
each year by automobiles and are a major cause of smog formation.
What is the volume of 1.00 t (1.00 Mg) of nitrogen dioxide at SATP?
SUMMARY
Answers
7. 2.0 mmol
8. (a) 50.4 L
(b) 114 kPa
9. 73 mL
10. 9.80 L
11. 539 kL
Gas Stoichiometry
Sample Problem 1
Hydrogen gas is produced when sodium metal is added to water.What mass of
sodium is necessary to produce 20.0 L of hydrogen at SATP?
Sample Problem 2
Recall the Haber process from Chapter 5 in which ammonia to be used as fertilizer
is produced from the reaction of nitrogen and hydrogen. What volume of
ammonia at 450 kPa pressure and 80°C can be obtained from the complete reaction
of 7.5 kg of hydrogen?
Understanding Concepts
1. What volume of oxygen at STP is needed to completely burn 15 g of
methanol in a fondue burner?
2. A Down’s Cell is used in the industrial production of sodium from the
decomposition of molten sodium chloride. A major advantage of this
process compared with earlier technologies is the production of the
valuable byproduct chlorine. What volume of chlorine gas is produced
(measured at SATP), along with 105 kg of sodium metal, from
the decomposition of sodium chloride?
3. Most combustion reactions use oxygen from the air (assume 20%
oxygen). What mass of propane from a tank can be burned using
125 L of air at SATP?
Answers
1. 16 L
2. 56.6 kL or 56.6 m3
3. 8.9 g
(a) 0.58 L