Question

calculate the mole fraction of a fractional distillation? How do I find the mole fractions of different distillations given only the refractive index, the temperature and which the distillation was acquired, and the makeup on the original solution before distillation?

the lab manual says to use P= (px * mol frac x)+(py * mol frac y)

but i don't know how I can find their partial pressure given that I don't know their mole fractions of the distillation since partial P=mole frac * vapor pressure.

Answer 1

As you try to separate a mixture of liquid compounds into two different fractions, you will obtain
the boiling point range of both components of your mixture .The better your separation,
more accurate your boiling points will be. Both boiling point and refractive index are physical
properties that are used to give some indication of their purity.This is really important
because the differences between their boiling points is very small & hence they are
temperature sensitive. Measure purity of the fractions and residue using index of refraction.

Mole % values can be determined from a standard Regression Curve relating Refractive Index
of known mixtures of solutions to the measured Refractive Index values of the distillate fractions.
Understand composition of sample based on index of refraction to get mole%.
Then convert mole% to mole fraction.

Then take down the literature values of Antoine equation parameters: A,B,C
and find the vapor pressure using Antoine equation ,
log₁₀ p = A - B/C+T
Now that you have vapor pressures and mole fractions you can calculate Partial pressures
with your equations.