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Homework Help! (Chemistry)

TSE said:
New question!!!!!!

How can you determine the molar mass of a gaseous compound if you do not know its molecular formula?
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is there any numbers given here? assuming you know the measurement of the gas in it's current form, you divide that by 22.4L (?) to get the mol.
 
Chundles said:
Something about the Ideal Gas Law rings a bell but I'm not sure. Been years since they bestowed that bloody degree on me.
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that's pv=nrt. here's the wiki article for a quick refresher. there were three constants for p,v and t (pressure, volume and temperature in kelvin (i think)) in a certain situation. n is the gas constant and n is the number of moles.
 
TSE said:
New question!!!!!!

How can you determine the molar mass of a gaseous compound if you do not know its molecular formula?
Click to expand...

The easiest method I can think of is to measure its density at STP. Then you can use the density in g/L X 22.4 L/mol to get a molar mass in g/mol. This works because 1 mol of any gas has a volume of 22.4 L at STP.

Alternately, you can measure the pressure, volume and temperature of a known mass of the gas. You will have P, V, and T from the ideal gas law (PV = nRT). You can solve for n, then use the mass of the gas / the number of moles (n) to get the molar mass.
 
TSE said:
STP was the correct answer guys! Thank you very much!
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i didn't think that was so easy as in just explaining the method. and yes, stp was the situation i was referring to in a previous post.

are you in high school or college btw? just asking so i can know what the difficulty of the exam is going to be on friday.
 
TSE said:
I'm a sophomore in high school.
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those were the days. that's when i start learning about mols and the such. my teacher at least taught us a method that made mols a bit easier to calculate.

and since you have a big quiz on friday, i wonder if you're ready.
 
Yea, I'm not sure if I am I will be studying for 2 hours tonight. I will tell you guys how the test goes. Thank you all for your help and I am sure this thread will be used by me some more after this unit.
 
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