# Chemistry help?

Discussion in 'Community Discussion' started by emt1, Apr 29, 2009.

1. ### emt1 macrumors 65816

Joined:
Jan 30, 2008
Location:
Wisconsin
#1
Anyone here good at chemistry?

I need the molar mass of an unknown gas.

A 45.95 gram sample is in a rigid container at 1.086 atm and 229.9K.

2. ### aethelbert macrumors 601

Joined:
Jun 1, 2007
Location:
Chicago, IL, USA
#2
Use the ideal gas law to get the total volume and then divide that by the constant ideal gas volume. Then you have the number of moles and go from there.

3. ### emt1 thread starter macrumors 65816

Joined:
Jan 30, 2008
Location:
Wisconsin
#3
If someone could begin to walk through the steps, I'd appreciate it.

4. ### aethelbert macrumors 601

Joined:
Jun 1, 2007
Location:
Chicago, IL, USA
#4
Ideal gas law is PV=nRT

First plug in numbers and solve for n to find out your total number of moles.

5. ### Cave Man macrumors 604

Joined:
Feb 12, 2007
Location:
Neander Valley, Germany; just outside Duesseldorf
6. ### emt1 thread starter macrumors 65816

Joined:
Jan 30, 2008
Location:
Wisconsin
#6
I don't have n or V.

Joined:
Feb 28, 2008

Joined:
Feb 6, 2007
#8
m/mm=PV/RT

Joined:
Sep 24, 2002
Location:
Utopia
10. ### aethelbert macrumors 601

Joined:
Jun 1, 2007
Location:
Chicago, IL, USA
#10
V=22.4n

11. ### SLC Flyfishing Suspended

Joined:
Nov 19, 2007
Location:
Portland, OR
#11
Seems to me like you might have too many unknowns to solve this, but assuming that we can use the molar volume of a gas for V then your molar mass should be 35.65249 g/mol which is pretty close to Chlorine.

The molar volume of a gas is 22.4 liters, so your equation would be:

(1.086 atm)(22.4L)/(0.0821 L*atm/mol*K)(229.9K)=n

n will be your number of moles which works out to be 1.289 mol.

you divide your given mass of 45.95 grams by the 1.29 mol to get a molar mass of 35.62 grams/mol. Chlorine (which is a gas at most temperatures) has a molar mass of 35.45 grams/mol.

But where I think this might all fall apart is that I believe that the stated temperature is just shy of Chlorine's vaporization point. So unless I'm mistaken, at that temperature and pressure, Chlorine should be a solid.

It's been like 3 years since I was in Gen Chem so you'll understand if I'm wrong here.

SLC

12. ### Telp macrumors 68040

Joined:
Feb 6, 2007
#12
Molar volume of a gas is only 22.4 L at standard temperature and pressure, I thought...Neither