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
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
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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