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### Topic: Determining Formula from Molecular mass?  (Read 1735 times)

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#### jennielynn_1980

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##### Determining Formula from Molecular mass?
« on: September 23, 2011, 04:44:29 PM »
Hi everyone.  I have figured out most of this question but the last part is really getting me.  I haven't been in a chemistry class for awhile so I am a little rusty.  If someone could tell me what direction to think in that would be great

A sample of 2.14 g of a gaseous organofluorine compound occupies a volume of  2.00 L at 25.5 C and 30.2 kPa.  What is the molar mass of this compound and what is it's formula?

So using PV=nRT
n= (0.298atm)(2.00L)/(0.08205 L atm K-1 mol-1)(298.65 K)
= 0.0243 mol

Then using M=m/n
M = 2.14g/0.0243 mol
= 87.9 g/mol

So I determined the molar mass but now how do I get the formula?

Thanks

#### Borek

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##### Re: Determining Formula from Molecular mass?
« Reply #1 on: September 23, 2011, 06:54:50 PM »
The only possible approach is by trial and error. Start with simple compounds (like CH3F) and see if they fit the molar mass.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### jennielynn_1980

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##### Re: Determining Formula from Molecular mass?
« Reply #2 on: September 23, 2011, 07:00:06 PM »
Thank you Borek.  I was trying to figure out how to do a percentage my mass setup but I wasn't getting far.