Question

acetone and methanol form ideal solution. at 25 degree C the vapor pressure of pure acetone and pure methanol is 0.342 atm and 0.188atm respectively. calculate the mole fraction of methanol in a solution that boils at 25 degree c.

Answer 1

The solution boils at 25 degree c. It means that the vapor pressure of solution is equal to 1 atmoshpehre (the atmospheric pressure)

Let X be the mole fraction of acetone. The mole fraction of methanol will be

The mole fraction of methanol

Here negative value for mole fraction is obtained. This suggests that the solution is non ideal.

If we start with idea solution of acetone and methanol, then the vapor pressure of solution should be in between the vapor pressure of pure acetone and pure methanol that is 0.342 atm and 0.188atm respectively. It cannot be 1 atm which is outside the range 0.188-0.342. Hence, this suggests non ideal behavior