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).

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?

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

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

Ah mole ratio lol nevermind

X = mole fraction.

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

a) To draw the Lewis structures for acetone (CH3COCH3) and carbon disulfide (CS2), we first need to count the total number of valence electrons for each molecule. Acetone has 10 valence electrons (4 from carbon, 4 from oxygen, and 2 from hydrogen), while carbon disulfide has 18 valence electrons (4 from carbon and 7 from each sulfur atom).

Acetone:
H
|
H - C - C - O - H
|
H

Carbon disulfide:
S
||
S - C - S

Now, let's explain the deviation from ideal behavior in terms of intermolecular forces. Raoult's Law applies to solutions where solute-solvent intermolecular forces are similar to solute-solute and solvent-solvent intermolecular forces. In this case, acetone and carbon disulfide have significantly different molecular structures and intermolecular forces.

Acetone has hydrogen bonding due to the presence of hydrogen atoms bonded to oxygen. Additionally, it also has dipole-dipole interactions between the oxygen atom and the carbon atoms. Carbon disulfide, on the other hand, is a nonpolar molecule with only London dispersion forces between the sulfur and carbon atoms.

The positive deviation from Raoult's Law in this solution occurs because the intermolecular forces between the solute and solvent (acetone and carbon disulfide) are weaker than the forces between solute-solute and solvent-solvent. As a result, the molecules in the solution have a higher vapor pressure than those predicted by Raoult's Law.

b) To calculate the vapor pressure of the solution if it behaved ideally, we can use Dalton's Law of partial pressures. According to Dalton's Law, the total vapor pressure of a solution is equal to the sum of the vapor pressures of each component, multiplied by their mole fractions.

Partial pressure of acetone (P1) = mole fraction of acetone (x1) * vapor pressure of acetone (P1°)
Partial pressure of carbon disulfide (P2) = mole fraction of carbon disulfide (x2) * vapor pressure of carbon disulfide (P2°)

Total vapor pressure of the solution (Ptotal) = P1 + P2

Given:
mole of acetone (CH3COCH3) = 0.60
mole of carbon disulfide (CS2) = 0.40
vapor pressure of acetone (P1°) = 349 mmHg
vapor pressure of carbon disulfide (P2°) = 501 mmHg

First, we need to calculate the mole fractions:
Mole fraction of acetone (x1) = 0.60 / (0.60 + 0.40) = 0.60
Mole fraction of carbon disulfide (x2) = 0.40 / (0.60 + 0.40) = 0.40

Now we can calculate the partial pressures:
Partial pressure of acetone (P1) = 0.60 * 349 mmHg = 209.4 mmHg
Partial pressure of carbon disulfide (P2) = 0.40 * 501 mmHg = 200.4 mmHg

Finally, we can calculate the total vapor pressure of the solution:
Total vapor pressure (Ptotal) = P1 + P2 = 209.4 mmHg + 200.4 mmHg = 409.8 mmHg

Thus, if the solution behaved ideally, the vapor pressure would be 409.8 mmHg.

c) To calculate the composition of the vapor in the vapor phase assuming ideal behavior, we can use the mole fraction equation again.

Mole fraction of acetone in the vapor phase = mole fraction of acetone (x1)
Mole fraction of carbon disulfide in the vapor phase = mole fraction of carbon disulfide (x2)

Given the mole fractions:
Mole fraction of acetone (x1) = 0.60
Mole fraction of carbon disulfide (x2) = 0.40

Therefore, in the vapor phase, the composition would be 60% acetone and 40% carbon disulfide.

d) For the non-ideal solution, we would expect the heat of solution to be positive. Non-ideal solutions often exhibit positive deviations from Raoult's Law, which means that the intermolecular forces between solute and solvent are weaker than those between solute-solute and solvent-solvent. In order to form a solution, energy is required to overcome the weaker intermolecular forces and mix the components together. This required energy is absorbed as heat, resulting in a positive heat of solution.