In a 197 mL flask, 0.286 g of an unknown gas condenses at 0.642 atm and 288K. What is the molecular weight of the gas? What equation do I use and please explain your procedure. Thx
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Hi Zane!
This question requires you to use the ideal gas equation PV=nRT where P represents pressure, V represents volume in liters, n represents moles, R represents the gas constant (most likely 0.08206L atm/moles K but ultimately depends on the units of pressure), and T represents the temperature in kelvin (K=C+273).
Knowing this equation, plug in all the variables you know are given in the problem: (0.642atm)(0.197L)=n(0.08206Latm/moles k)(288K). Notice that I did two things here: I converted mL to L and I also inserted the value of the gas constant. Don't worry about this value because it is always the same so you can either memorize it for future problems or look it up. Now we have one missing variable, n, and that is the amount of moles of the gas. Use algebra to solve for n and you should get about 5.35x10^-3 moles of the gas (this is in significant figures). Now remember that we were given the mass because now to find the molecular weight, we just divide grams by moles: (0.286g)/(7.53x10^-3 moles) = about 53.4 g/mole. So the molecular weight of the gas is 53.4 grams per mole.
I hope this helped and feel free to ask any more questions if this was confusing :)
This question requires you to use the ideal gas equation PV=nRT where P represents pressure, V represents volume in liters, n represents moles, R represents the gas constant (most likely 0.08206L atm/moles K but ultimately depends on the units of pressure), and T represents the temperature in kelvin (K=C+273).
Knowing this equation, plug in all the variables you know are given in the problem: (0.642atm)(0.197L)=n(0.08206Latm/moles k)(288K). Notice that I did two things here: I converted mL to L and I also inserted the value of the gas constant. Don't worry about this value because it is always the same so you can either memorize it for future problems or look it up. Now we have one missing variable, n, and that is the amount of moles of the gas. Use algebra to solve for n and you should get about 5.35x10^-3 moles of the gas (this is in significant figures). Now remember that we were given the mass because now to find the molecular weight, we just divide grams by moles: (0.286g)/(7.53x10^-3 moles) = about 53.4 g/mole. So the molecular weight of the gas is 53.4 grams per mole.
I hope this helped and feel free to ask any more questions if this was confusing :)
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you are given volume, pressure, temperature. and mass. I would feel like this would be the ideal gas equation, PV=nRT.
however you are trying to find molecular weight. the "n" in (PV=nRT) represents moles, and moles = grams / molecular weight.
SOOO. PV= (grams of gas) R T / Molecular weight
all i did was change the N into grams / molecular weight now you plug it all in.
P= .642 atm
V= 197 ml convert this into liters = .197 L
GRAMS= .286
however you are trying to find molecular weight. the "n" in (PV=nRT) represents moles, and moles = grams / molecular weight.
SOOO. PV= (grams of gas) R T / Molecular weight
all i did was change the N into grams / molecular weight now you plug it all in.
P= .642 atm
V= 197 ml convert this into liters = .197 L
GRAMS= .286
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