# 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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3. 👁 135
1. Use PV = nRT to solve for n.
Then n = grams/molar mass.

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posted by DrBob222
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.

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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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posted by ricky

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