Question

what are the partial and total vapor pressures of a solution obtained by mixing 35.8 g of benzene C6H6 and 56.7 g of toluene C7H8 at 25C? at 25C the vapor pressure of c6h6 = 95.1 mmHg and the vapor pressure of C7H8= 28.4 mmHg

molar masses are c6h6= 78.11 g/mol and c7h8 = 92.13

Answer 1

Moles of benzene = mass of benzene / Molar mass of Benzene = ( 35.8 /78.11) = 0.458328

Moles of toulene = ( 56.7/92.13)= 0.615435

total moles ( both) = 0.458328+0.615435 =1.07376

mol fraction of benzene = ( benzene moles/ total moles) = ( 0.458328/1.07376) = 0.427

toulene mol fraction = 1-0.427 = 0.573

Partial Pressure of benzene = mol fraction of benzene x Pure vapor pressure of benzene

        = ( 0.427 x 95.1) = 40.6 mm Hg

partial pressure of toulene = ( 0.573 x 28.4) = 16.273 mm Hg

Toal vapor pressure = sum of partial pressures = ( 40.6+ 16.273) = 56.873 mm Hg