"Published in Newark, California, USA"
If ethanol and methanol are mixed 50/50 by weight at 60°C, and the solution assumed ideal, what is the composition of the vapor above the solution?
Solution:
From the given word problem, it is about Dalton's Law of Partial Pressure because it involves the mixture of gas vapors. Ethanol and methanol are mixed in equal proportion or amount.
Basis: 100 grams of the mixture
Let's consider first the liquid phase. The number of moles of ethanol and methanol in the solution are
Next, consider the gas or vapor phase. From Saturated Vapor Pressure Data, the vapor pressure of pure ethanol at 60°C is 0.461395 atm and for the pure methanol is 0.832997 atm. Hence, the partial pressure of ethanol is
and the partial pressure of methanol is
Therefore, the % ethanol in the vapor is
and the % methanol in the vapor is
