Ethanol % in vapor determination

Feb 2017
1
0
TX
I have a temperature probe in a stream of vapor coming off a boiling ethanol solution, and a barometer monitoring ambient pressure. I need to convert the vapor temperature (boiling point) into the % ethanol in the vapor with correction for ambient pressure.

My objective is to have a single equation I can plug these 2 variables into to get the current % ethanol.

Help is greatly appreciated!

Known values:
Ethanol mixture boiling point[vapor temp] (Ex: 81C)
Current barometric pressure (Ex: 766.8 mmHg)

Ethanol boiling point 78.37 C (at 1 ATM/760mmHg)
water boiling point 100C (at 1 ATM/760mmHg)
proportionality constant (Kb) of ethanol 1.19
proportionality constant (Kb) of water 0.512

formula for the boiling point elevation
ΔTb=Kbm (where m is moality of the solution)

From: http://www.dummies.com/education/science/chemistry/how-to-elevate-and-calculate-boiling-points-of-solvents/

(other info that may not be necessary)
Current room temperature (Ex: 28C)
Current Altitude (Ex: 120m above sea level)
 
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