EXAMPLE
#1:
Q:
At 28 oC and 0.974 atm,
1.00 L of gas has a mass of 5.16 grams. What is the molar mass of this
gas?
A: P V = n R T * given T, P, V
& R is constant, we must solve for n *
n = P V = (0.974 atm) (1.00 L) =
0.0394 moles
R T (0.0821 L atm/mole K) (301 K)
moles = grams
MM
MM = grams = 5.16 grams = 131 g/mole
moles 0.0394 moles
EXAMPLE
#2:
Q: What
is the molar mass of a gas if 0.427 grams of the gas occupies a volume of 125 mL at 20.0 oC
and 0.980 atm? (A: 83.8 g/mole)
*Honors
only
EXAMPLE
3:
Q: What
is the density of argon gas, Ar, at a pressure of 551
torr and a temperature of 25 oC?
A:
density = mass
P V = (mass/MM) R T
volume
P = (mass/MM) R T
P MM = mass
Density = P (MM)
V
R T V
R T
P = 551 torr x 1 atm =
0.725 atm
T = 25 oC + 273 = 298 K
760 torr
D = (0.725 atm) (39.9 g/mole)
= 1.18 g/L
(0.0821 L atm/mole
K) (298 K)
EXAMPLE
4:
Q: The
density of a gas was found to be 2.0 g/L at 1.50 atm
and 27 oC. What is the molar mass of
the gas? (A: 33 g/mole)