# Problem: A solution contains 4.08 g of chloroform (CHCl3 ) and 9.29 g of acetone (CH3 COCH3 ). The vapor pressures at 35 oC of pure chloroform and pure acetone are 295 torr and 332 torr, respectively.Assuming ideal behavior, calculate the vapor pressure of chloroform.

###### FREE Expert Solution

We’re being asked to determine the vapor pressure of a solution that contains 4.08 g of chloroform (CHCl3) and 9.29 g of acetone (CH3COCH3) assuming ideal behavior.

Recall that the vapor pressure of an ideal solution can be given by Raoult’s Law

The given solutions are composed of chloroform and acetone, which are both volatile. For a solution with volatile solute and solvent, Raoult’s Law is given as:

where P˚ = vapor pressure and χ = mole fraction. This means that for this solution:

Mole fraction is given by:

where i = van’t Hoff factor. We first need to determine the mole fraction of the solute and solvent for each solution.

To do so, we need to find the number of moles from their molar mass:

mass (molar mass) → moles

Molar Mass:

CHCl3            1 C x 12.01 g/mol = 12.01 g/mol
1 H  x 1.01 g/mol = 1.01 g/mol

3 Cl x 35.45 g/mol = 106.35 g/mol
_____________________________
Sum =
119.37 g/mol

CH3COCH3    3 C x 12.01 g/mol = 36.03 g/mol
6 H  x 1.01 g/mol = 6.06 g/mol

1 O x 16.00 g/mol = 16.00 g/mol

_____________________________
Sum =
58.09 g/mol

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###### Problem Details

A solution contains 4.08 g of chloroform (CHCl3 ) and 9.29 g of acetone (CH3 COCH3 ). The vapor pressures at 35 oC of pure chloroform and pure acetone are 295 torr and 332 torr, respectively.

Assuming ideal behavior, calculate the vapor pressure of chloroform.

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the The Colligative Properties concept. You can view video lessons to learn The Colligative Properties. Or if you need more The Colligative Properties practice, you can also practice The Colligative Properties practice problems.