1. How many air molecules are in a 15.0×12.0×10.0 ft room? Assume atmospheric pr
ID: 521019 • Letter: 1
Question
1.
How many air molecules are in a 15.0×12.0×10.0 ft room? Assume atmospheric pressure of 1.00 atm, a room temperature of 20.0 C, and ideal behavior.
Volume conversion:There are 28.2 liters in one cubic foot.
2.
A deep-sea diver uses a gas cylinder with a volume of 10.0 L and a content of 51.1 g of O2 and 33.1 g of He. Calculate the partial pressure of each gas and the total pressure if the temperature of the gas is 17 C. Express the pressures in atmospheres to three significant digits separated by commas.
3.
A gas of unknown molecular mass was allowed to effuse through a small opening under constant-pressure conditions. It required 125 s for 1.0 L of the gas to effuse. Under identical experimental conditions it required 27 s for 1.0 L of O2 gas to effuse. Calculate the molar mass of the unknown gas. (Remember that the faster the rate of effusion, the shorter the time required for effusion of 1.0 L; that is, rate and time are inversely proportional.)
Express your answer using two significant figures.
Thank you.
Explanation / Answer
Q1.
air molecules...
V = 15*12*10 = 1800 ft3 --> 50970.32 liters
P = 1 atm; T = 20°C = 293 K
apply ideal gas law
PV = nRT
n = PV/(RT) = 1*50970.32 /(0.082*293) = 2121.4650 moles of air
1 mol = 6.022*10^23
2121.4650 mol --> 2121.4650*( 6.022*10^23) = 1.27754*10^27 molecules of air
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