1.) A balloon contains 3.56L of helium at a temperature of 28.8 o C and a pressu
ID: 1006642 • Letter: 1
Question
1.) A balloon contains 3.56L of helium at a temperature of 28.8oC and a pressure of 1.03 atm. What is the mass of helium in the balloon?
2.) At a certain temperature the vapor pressure of water is 21 torr. The pressure of the gas in a soda bottle (carbonated water) is measured to be 864 torr. What is the pressure (in torr) of the carbon dioxide in the soda bottle?
3.) A sample of gas contains 3.35 moles of oxygen, 1.09 moles of nitrogen, and 1.68 moles of carbon dioxide. If the total pressure is 3.51 atm, what is the partial pressure of the oxygen in atm?
Explanation / Answer
(1)We know that ideal gas equation is PV = nRT
Where
T = Temperature = 28.8oC = 28.8+273 = 301.8 K
P = pressure = 1.03 atm
n = No . of moles = ?
R = gas constant = 0.0821 L atm / mol - K
V= Volume of the gas = 3.56 L
Plug the values we get n = PV/(RT)
= 0.148 moles
We know that number of moles , n = mass/molar mass
So mass of He in the ballon , m = number of moles x molar mass of He
= 0.148 mol x 4(g/mol)
= 0.592 g
Therefore the mass of He in the ballon is 0.529 g
(2) Given the pressure of the gas in the soda bottle is , P = 864 torr
The vapour pressure of the water is , P' = 21 torr
So the pressure of CO2 in the bottle , P'' = P - P'
= 864 - 21
= 843 torr
Therefore the pressure of Carbondioxide in the bottle is 843 torr
(3) Total number of moles , N = number of moles of N2 + number of moles of O2 + number of moles of CO2
= 1.09+3.35+1.68
= 6.12 moles
Mole fraction of oxygen , X = number of moles of oxygen / total number of moles
= 3.35 / 6.12
= 0.547
So partial pressure of Oxygen , p = total pressure x mole fraction of oxygen
= 3.51 atm x 0.547
= 1.92 atm
Therefore the partial pressure of oxygen is 1.92 atm
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