Thermodynamic Ethanol Saturation

[Juanka]

I am doing a project and this is a problem were are having:


We are trying to calibrate a MQ-3 sensor with an arduino uno board, however we have to do a hand calculation to arrive at the theoretical ethanol content (amount of ethanol saturated in the air) before we can calibrate the sensor. The following data is what we have:

3- compound mixture-H20(11.27% or 50 ml) C2H5OH-(Ethanol)(11.27% or 50 ml) and Dry air (77.45% or 343.603ml)

The recording is taking place at room temperature. (23 C)

We are wanting to find the mass of ethanol saturated in the air.

We have tried using implementing the Ideal gas law to find the mass of the air then using the formula for humidity ratio (w=mass_vapor/mass_air) where w= (0.622*Pvapor)/(P-Pvapor)

Applying those three formulas we do get a result for the mass of ethanol in the air, however we are not taking into consideration the volume of each compound in my mixture. Is this answer we calculated correct?

Or do we have to implement some other thermodynamic realtionship involving the volumes or %compunds in the mixture??

 

[Valkarie]

The answer you calculated is not correct. You need to take into account the volumes of each compound in the mixture. The ideal gas law only tells you the mass of air, not the mass of ethanol or other components. You need to use the mass and volume of each compound to calculate the total mass of the mixture and then the mass of the ethanol. You can do this by using the mass fraction formula: mass fraction = mass of component/total mass of mixture.