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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: hwgw on January 26, 2008, 08:25:42 PM

Title: [SOLVED] Gases -- Finding volume percentage
Post by: hwgw on January 26, 2008, 08:25:42 PM

Hi,

I have a question where I am given a sample of a mixture of gases (C2HF5 and C2H3F3) and was told to find the volume percentage of one gas.

Pressure = 0.449 atm
T= 288.15 K
Density= 1.79 g/L

I have also found the average molecular mass to be 94.266 amu.

So how can i approach this question to find the volume percentage of C2H3F3?
Do i use PV=nRT?

Thanks

Title: Re: Gases -- Finding volume percentage
Post by: Yggdrasil on January 27, 2008, 01:11:42 PM

What's the molecular mass of C2HF5?  What's the molecular mass of C2H3F3?  What ratio of the two gasses gives an average molecular mass of 94.266?

Title: Re: Gases -- Finding volume percentage
Post by: hwgw on January 27, 2008, 06:22:35 PM

When asking for average molecular mass, is that (mass 1 + mass 2) / 2 ?

Title: Re: Gases -- Finding volume percentage
Post by: Kryolith on January 27, 2008, 06:30:03 PM

No. You need to solve two equations:

x*M(C₂HF₅)+y*M(C₂H₃F₃)=94.266 g/mol
x+y=1

x=percentage of C₂HF₅
y=percentage of C₂H₃F₃
M=molar mass
94.266 g/mol = average molar mass of the mixture

Title: Re: Gases -- Finding volume percentage
Post by: hwgw on January 28, 2008, 01:55:03 AM

Thanks, that was really helpful. 8)

Title: Re: [SOLVED] Gases -- Finding volume percentage
Post by: Kryolith on January 28, 2008, 03:47:28 AM

You're welcome  :)