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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: abcdepik on November 16, 2011, 03:47:29 PM

Title: Partial Pressure and Proof
Post by: abcdepik on November 16, 2011, 03:47:29 PM

Hi, I have a question on one of my chemistry problem sets, and I have no clue how to approach this. I tried different things but they don't seem right...

The question is:
Assuming that 30 proof alcohol contains only water and ethanol, what is the partial pressure of ethanol in the headspace of the bottle? (The density of ethanol is 0.78g/mL)

I know raoults law is often used to find partial pressure: P(solvent)= X(solvent) P*(solvent)

But I'm not sure how this could be used for this question.

I was also given that the mixing ratio of ethanol is 5ppbv= 5.0 x 10^-9 atm


Any help will be greatly appreciated! Thanks in advance!

Title: Re: Partial Pressure and Proof
Post by: fledarmus on November 16, 2011, 03:55:17 PM

Do you know what "proof" means in the context of alcohols?

Title: Re: Partial Pressure and Proof
Post by: abcdepik on November 16, 2011, 04:50:07 PM

It is DOUBLE the  volume% of the alcohol content in a sample...

so it would be Proof= (v ethanol/ v water)% x 2

and if you wanted v ethanol= (Proof/2)%   
at least this is what i have gathered from various sources...our prof didn't give us any additional information on this example.