# Molecular Formulas

1. Dec 8, 2003

### babbagee

Analysis of a newly discovered gaseous silicon-fluorine compound shows that it contains 33.01 mass % silicon. At 27oC 2.60g of the compound exerts a pressure of 1.50 atm in a 0.250-L vessel. What is the molecular formula of the compound?
I guess PV=nRT needs to be used. P,V,R, and T are given, i guess the only thing to sove for is n. That gives me the total moles of silicon fluorine. But i dont know where to go after that.

Thanks

2. Dec 8, 2003

### himanshu121

First of all find molecular wt of comp

now find empirical formula

n= mol. wt / empirical formula

and hence the formula for compound as $$(Si_xF_y)_n$$

3. Dec 8, 2003

### babbagee

Does this look right??

m=RT/PV = ((2.60)(.0821)(300))/((1.50)(.250)) = 170.7
Mol wt=170.7

33.01 %Si -100 = 66.99%F

33.01g Si and 66.99gF

33.01gSi(1mol/28.09gSi)=1.17mol
66.99gF(1mol/19.00gF)=3.52mol
Si1.17F3.52
emp formula = SiF3
Mol wt/emp wt = 170.7/85 = 2
mol formula = Si2F6

Is this correct.

4. Dec 8, 2003

Yes it is