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Molecular Formulas

  1. Dec 8, 2003 #1
    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. jcsd
  3. Dec 8, 2003 #2
    First of all find molecular wt of comp

    now find empirical formula

    n= mol. wt / empirical formula

    and hence the formula for compound as [tex](Si_xF_y)_n[/tex]
     
  4. Dec 8, 2003 #3
    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.
     
  5. Dec 8, 2003 #4
    Yes it is
     
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