1.experiment shows that a 116 mL gas sample has a mass of 0.172 g at a pressure
ID: 1010241 • Letter: 1
Question
1.experiment shows that a 116 mL gas sample has a mass of 0.172 g at a pressure of 717 mmHg and a temperature of 34 C. What is the molar mass of the gas? 2.A gas mixture with a total pressure of 770 mmHg contains each of the following gases at the indicated partial pressures: 135 mmHg CO2, 210 mmHg Ar, and 190 mmHg O2. The mixture also contains helium gas.What is the partial pressure of the helium gas? 3.What is the mole fraction of oxygen gas in air (see table 5.3 in the textbook)? Express your answer using two significant figures. 4.What volume of air contains 14.9 g of oxygen gas at 273 K and 1.00 atm? Express your answer using two significant figures. 5.A heliox deep-sea diving mixture contains 2.0 g of oxygen to every 98.0 g of helium.What is the partial pressure of oxygen when this mixture is delivered at a total pressure of 7.5 atm ? Express your answer using two significant figures.
Explanation / Answer
from ideal gas equation
PV = nRT
p = pressure of the gas = 717/760 = 0.943 atm
T = temperature of the gas = 34+273.15 = 307.15 k
R = ideal gas constant = 0.0821 L.atm.k-1.mol-1
V = volume of gas = 0.116 L
n = No of mol of gas = weight / mwt = (0.172/w)
0.943*0.116 = (0.172/w)*0.0821*307.15
W = molarmass of gas = 39.65 g/mol
2) A.
daltons law of partial pressures
Ptotal = PCO2 + PAr + PO2 + PHe
770 = 135+210+190+x
x = 235 mmhg = pHe
3) partal pressure = molefraction*Ptotal
190 = x*770
x= 0.25
4) volume of gas = nRT/P = (14.9/32)*0.0821*273/(190/760)
= 41.74 L
5) molafraction of O2 = (2/32)/((2/32)+(98/4))
= 0.00254
Po2 = xo2*ptotal
= 0.00254*7.5
= 0.019 atm
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