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:


Psolution = P°1X1+P°2X2


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


Psolution = P°CH3Cl3XCH3Cl3+P°CH3COCH3XCH3COCH3


Mole fraction is given by:


χsolute = moles solutei·moles solute+moles solvent


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.

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