1. 2. A compressed air tank carried by a scuba diver has a volume of 8.0L and a pressure of 140
atm at 20.0°C. What is the volume in the tank (in liters) at STP? (5) 3. If 20.0 g of N2 () has a
volume of 40 L and a pressure of 4560 mmHg, what is the Celsius temperature? (5) 4. An
unknown gas is placed in a 1.500 L bulb at a pressure of 0.468 atm and a temperature of
22.5°C, and is found to weugh0.9847 g. What is the molecular weight of the gas? (5)
Solution
2) At STP, T2 = 273.15 K and P2 = 1 atm
For fixed amount of gas,
P1 * V1 / T1 = P2 * V2 / T2
140 * 8.0 / 293 = 1 * V2 / 273.15
V2 = 1044 L
so volume in the tank at STP is 1044 L
3) 20 gm N2 = mass / molar mass = 20 / 28 = 0.714 mole.
1 atm = 760 mm Hg.
Ideal gas equation is
PV = nRT
(4560 / 760) atm * 40 L = 0.714 mole * 0.0821 L-atm / mole K * T
T = 4094 K = 4094 - 273 = 3821 oC
so celcius temperature is 3821 oC.
4)

2. Let molecular weight of gas is M gm / mole.
moles of gas = 0.9847 / M mole.
ideal gas equation is
PV = nRT
0.468 * 1.500 = (0.9847 / M) * 0.0821 * 295.5
M = 34.03 gm / mole.
therefore, molecular weight of gas is 34.03 gm / mole.