Chemistry

What is the molecular weight of a gas if a 15.0g sample has a pressure of 836 mm Hg at 25.0 degrees C in a 2.00 L flask?

a)167
b)1.35
c)176
d)11.1
e)none of the above

Please explain... I need to understand how to do this. Thanks.

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  1. Use PV = nRT to solve for n.
    Then n = grams/molar mass.

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  2. I'm still confused... I know that:
    P=1.1 atm
    V=2.00 L
    n=?
    R= I think .0821
    and
    T= ?

    I have no idea how to change 15.0g to moles, since I do not know what the element is to look at the atomic mass--I know that one mole is avagadro's number, but I'm still really not sure what to do here.

    Please help...

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  3. T- 25+273 = 298k

    n=PV/RT

    n= 1.1 atm*2.00 l/ (0.0821 (L*atm/ mol*k) *298k)
    n=0.0899mol
    MW= 5.0g/0.0899mol

    =167amu

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