A sample of nitrogen gas kept in a container of volume 2.3 L and at a temperature of
32°C exerts a pressure 4.7 atm. Calculate the number of moles of gas present.
(8
points)
1
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PV=nRT
4.7 atm x 2.3 L = n x .0821*305K
10.81 = n x 25.04
N = .43 mols
(Reference: Chang 5.31)
5.What volume will 5.6 moles of sulfur hexafluoride (SF6) gas occupy if the temperature and pressure of the gas are 128°C and 9.4 atm? (8 points)
6.
A gas-filled balloon having a volume of 2.50 L at 1.2 atm and 25°C is allowed to rise
to the stratosphere (about 30 km above the surface of Earth), where the temperature
and pressure are –23°C and 3.00 × 10
–3
atm, respectively. Calculate the final volume
of the balloon.
(8 points)
(Reference: Chang 5.35)
1.2 atm x 2.50L/ 298K = 3.00x10
-3
atm x V2 / 250K
0.0007 x 250K = 2.5175 / 3.00 x 10
-3
atm = 8.39x10
-4
= 839 L
7.
A 2.10-L vessel contains 4.65 g of a gas at 1.00 atm and 27.0°C. (a) Calculate the
density of the gas in grams per liter. (b) What is the molar mass of the gas?
(10
points)
(Reference: Chang 5.47)
PV/RT= 1.00 x 2.10 / .08206 x 300 = .0853
4.56g / .0853mol = 54.5g/mol
54.5 x 1.00 / .08206 x 300 = 2.21g/L
8.
A certain anesthetic contains 64.9 percent carbon, 13.5 percent hydrogen, and 21.6
percent oxygen by mass. At 120°C and 750 mmHg, 1.00 L of the gaseous compound
weighs 6.90 g. What is the molecular formula of the compound?
(10 points)
PV=nRT
n=PV/RT= (0.987 atm x 1.00 L)/(0.082 x 392.3 K) = 0.0307 mols
mols = mass/mw
0.0307 mols = 6.90 / mw

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