An example of a solution that exhibits a positive deviation from Raoult’s Law (total pressure is greater than expected) is a solution of acetone (CH3COCH3) and carbon disulfide (CS2).

Question

a) Draw Lewis structures for these molecules. Explain the deviation from ideal behavior in terms of intermolecular forces.

b) A solution composed of 0.60 mole of acetone and 0.40 mole of carbon disulfide has a vapor pressure of 615 mmHg at 35.2 degrees Celsius. What would the vapor pressure be if the solution behaved ideally? The vapor pressures of the pure solvents at 35.2 degrees Celsius are:
acetone = 349 mmHg and carbon disulfide = 501 mmHg.

c) Again assuming ideal behavior, what would be the composition of the vapor in the vapor phase?

d) For the non-ideal solution, would you expect the heat of solution to be positive or negative?

Answer 1

a) We can't draw structures on this board.
b) XCS2 = n CS2/total mols.
Xacaetone = n acetone/total mols.
Pacetone = Xacetone*Po acetone.
PCS2 = XCS2*Po CS2
Ptotal = PCS2 + Pacetone.

c) Xacetone in vapor = Pacetone/Ptotal
XCS2 in vapor = PCS2/Ptotal

Answer 2

It's probably really obvious, but what does the X signify in part B? I know P is pressure. And thanks again for helping.

Answer 3

Ah mole ratio lol nevermind

Answer 4

X = mole fraction.
In a solution of mols a and mols b, then
Xa = moles a/(mols a + mols b).