Exercises 4790 *61.Assume that unpolluted air has the composition shown in
Table 12-2. (a) Calculate the number of molecules of N 2 ,
of O 2 , and of Ar in 1.00 L of air at 21°C and 1.00 atm.
(b) Calculate the mole fractions of N 2 , O 2 , and Ar in the
air.
*062.Individual samples of O 2 , N 2 , and He are present in three
2.25-L vessels. Each exerts a pressure of 1.50 atm. (a) If
all three gases are forced into the same 1.00-L container
with no change in temperature, what will be the result-
ing pressure? (b) What is the partial pressure of O 2 in the
mixture? (c) What are the partial pressures of N 2 and He?
*063.Hydrogen was collected over water at 20°C and 755 torr.
The volume of this gas sample was 45.3 mL. What vol-
ume would the dry hydrogen occupy at STP?
*064.A nitrogen sample occupies 447 mL at STP. If the same
sample were collected over water at 25°C and 750. torr,
what would be the volume of the gas sample?
0 *65.A study of climbers who reached the summit of Mt. Ever-
est without supplemental oxygen revealed that the partial
pressures of O 2 and CO 2 in their lungs were 35 torr and
7.5 torr, respectively. The barometric pressure at the sum-
mit was 253 torr. Assume that the lung gases are saturated
with moisture at a body temperature of 37°C. Calculate
the partial pressure of inert gas (mostly nitrogen) in the
climbers’ lungs.
*066.A 4.00-L flask containing He at 6.00 atm is connected to
a 3.00-L flask containing N 2 at 3.00 atm and the gases
are allowed to mix. (a) Find the partial pressures of each
gas after they are allowed to mix. (b) Find the total pres-
sure of the mixture. (c) What is the mole fraction of
helium?
*067.A 3.46-liter sample of a gas was collected over water on
a day when the temperature was 21°C and the baromet-
ric pressure was 718 torr. The dry sample of gas had a
mass of 4.20 g. What is the molecular weight of the gas?
At 21°C the vapor pressure of water is 18.65 torr.Stoichiometry in Reactions Involving Gases
*068.During a collision, automobile air bags are inflated by the
N 2 gas formed by the explosive decomposition of sodium
azide, NaN 3.
2NaN 3 88n2Na3N 2
What mass of sodium azide would be needed to inflate a
30.0-L bag to a pressure of 1.40 atm at 25°C?
*069.Assuming the volumes of all gases in the reaction are mea-
sured at the same temperature and pressure, calculate the
volume of water vapor obtainable by the explosive reac-
tion of a mixture of 440. mL of hydrogen gas and 325
mL of oxygen gas.
0 *70.One liter of sulfur vapor, S 8 (g), at 600°C and 1.00 atm is
burned in excess pure oxygen to give sulfur dioxide gas,
SO 2 , measured at the same temperature and pressure.
What mass of SO 2 gas is obtained?*071.Calculate the volume of methane, CH 4 , measured at- K and 815 torr, that can be produced by the bacte-
rial breakdown of 1.00 kg of a simple sugar.
C 6 H 12 O 6 88n3CH 4 3CO 20 *72.A common laboratory preparation of oxygen isMnO 2
2KClO 3 (s)8888n2KCl(s)3O 2 (g)
heatIf you were designing an experiment to generate four bot-
tles (each containing 250. mL) of O 2 at 25°C and 755
torr and allowing for 25% waste, what mass of potassium
chlorate would be required?
*073.Many campers use small propane stoves to cook meals.
What volume of air (see Table 12-2) will be required to
burn 11.5 L of propane, C 3 H 8? Assume all gas volumes
are measured at the same temperature and pressure.C 3 H 8 (g)5O 2 (g)88n3CO 2 (g)4H 2 O(g)0 *74.If 2.00 L of nitrogen and 5.00 L of hydrogen were allowed
to react, how many liters of NH 3 (g) could form? Assume
all gases are at the same temperature and pressure, and
that the limiting reactant is used up.N 2 (g)3H 2 (g)88n2NH 3 (g)0 *75.We burn 15.00 L of ammonia in 20.00 L of oxygen at
500.°C. What volume of nitric oxide, NO, gas can form?
What volume of steam, H 2 O(g), is formed? Assume all
gases are at the same temperature and pressure, and that
the limiting reactant is used up.4NH 3 (g)5O 2 (g)88n4NO(g)6H 2 O(g)*076.What mass of KNO 3 would have to be decomposed to
produce 21.1 L of oxygen measured at STP?heat
2KNO 3 (s)888n2KNO 2 (s)O 2 (g)*077.Refer to Exercise 76. An impure sample of KNO 3 that
had a mass of 50.3 g was heated until all of the KNO 3
had decomposed. The liberated oxygen occupied 4.22 L
at STP. What percentage of the sample was KNO 3?
Assume that no impurities decompose to produce
oxygen.
0 *78.Heating a 5.913-g sample of an ore containing a metal
sulfide, in the presence of excess oxygen, produces 1.177
L of dry SO 2 , measured at 35.0°C and 755 torr. Calcu-
late the percentage by mass of sulfur in the ore.
0 *79.The following reactions occur in a gas mask (a self-
contained breathing apparatus) sometimes used by under-
ground miners. The H 2 O and CO 2 come from exhaled
air, and O 2 is inhaled as it is produced. KO 2 is potassium
superoxide. The CO 2 is converted to the solid salt