So we were given this question forever ago in my class, and he said we would go over it on a later day in class, but whether he forgot or I wasn't there I never saw the answer to it. And now, school is over for the summer so I can't ask him, but it's been bugging me, so hopefully someone here will know what to do.
A series of measurements are made in order to determine the molar mass of an unknown gas. First, a flask is evacuated and found to weigh 134.567 g. It is then filled with the gas to a pressure of 735 mm Hg at 31 degrees C and found to weigh 1067.9 g. (The density of the water at this temperature is 0.997 g/ml.) Assuming that the ideal-gas equation applies, calculate the molar mass of the unknown gas.
Found the below response, bolded mine, by searching your question with a straight cut and paste, I'd link it but it doens't have a specified address for some reason:
A series of measurements are made in order to determine the molar mass of an unknown gas. First, a large flask is evacuated and found to weigh 134.567 g. It is then filled with the gas to a pressure of 735 torr at 31°C and reweighed; its mass is now 137.456 g. Finally, the flask is filled with water at 31°C and found to weigh 1067.9g. The density of water at this temperature is 0.997 g/mL. Assuming that the ideal-gas equation applies, what is the molar mass of the unknown gas.
PV=nRT moles = grams/molar mass
PV=(g/MM)RT
Molar Mass = gRT/PV
MM=gRT/PV
Mass of gas = 137.456-134.567 = 2.889g
1067.9-134.567=933.3g H2O
933.3g/0.997=936.14mL H2O <--- Volume of container
Volume of container = .9361L
735torr = 0.967atm
MM = (2.889g * 0.0821L*atm/mol*K * 304K)/ (0.967atm * 0.9361)
MM = 79.7g/mol
So just checking, what with the water and all, did you leave that out or did the original question leave it out?
The intuitive mind is a sacred gift and the rational mind is a faithful servant. We have created a society that honors the servant and has forgotten the gift.
- Albert Einstein
King of Cairhien 20-7-2
Chancellor of the Landsraad, Archduke of Is'Mod
- Albert Einstein
King of Cairhien 20-7-2
Chancellor of the Landsraad, Archduke of Is'Mod
This message last edited by Isaac on 09/05/2011 at 07:20:08 PM
Chemisty Question
- 09/05/2011 06:11:03 PM
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Isn't there some kind of information missing? Like a volume?
- 09/05/2011 07:07:49 PM
431 Views
Yeah, it seemed like the water was kind of randomly thrown in there. I gave all the info I had. *NM*
- 09/05/2011 08:54:30 PM
227 Views
Seems like a measurement on water is left out here
- 09/05/2011 07:18:58 PM
818 Views
Boba Fett smiley is irritating
That was about what I thought. I assumed I was missing some info.
- 09/05/2011 08:50:00 PM
563 Views
Re: That was about what I thought. I assumed I was missing some info.
- 09/05/2011 09:29:36 PM
467 Views