At a given temperature, the vapor pressure of pure acetone (CH3COCH3, 58.00 g/mol) is 342 torr. At the same temperature, the vapor pressure of pure chloroform (CHCl3, 119.35 g/mol) is 230 torr. Consider a solution containing 23.2 g of acetone and 73.8 g of chloroform. Calculate the total vapor pressure above the solution (in torr to 0 decimal places)

Total vapor pressure = 274 torr

Explanation:

According to Raoult's law, the partial pressure of a volatile compound in a mixture of two volatile components is

PA = Xa PºA where PA = partial pressure of component A

XA = mole fraction of A = mol A / (molA + Mol B)

PºA = vapor pressure of pure A

and the total pressure will be given by the sum of the partial pressures.

mol CH3COCH3 = 23.2 g / 58 g/mol = 0.40 mol

mol CHCl3 = 73.8 g / 119.35 g/mol = 0.62 mol

total mol = 0.40 mol + 0.62 mol = 1.02 mol

XCH3COCH3 = 0.40 mol / 1.02 mol = 0.39

XCHCl3 = 0.62 mol / 1.02 mol = 0.61

PCH3COCH3 = 0.39 x 342 torr = 133.4 torr

PCHCl3 = 0.61 x 230 torr = 140.3 torr

Ptotal = 133.4 torr + 140.3 torr = 274 torr