Question

A solution contains 3.95 g of carbon disulfide (CS2, molar mass = 76.13 g/mol) and 2.43 g of acetone ((CH3)2CO, molar mass = 58.08 g/mol). The vapor pressure of pure carbon disulfide and acetone at 35 o C are 515 torr and 332 torr, respectively. Assuming ideal solution behavior, calculate the vapor pressure of each of the components and the total vapor pressure above the solution. The total vapor pressure above the solution at 35 o C was experimentally determined to be 645 torr. Is the solution ideal? If not, indicate whether the solution deviates from Raoult’s law in a positive or negative manner

Answer 1

The solution is not ideal and shows a positive deviation from Raoult’s law since Psolution (experimental) > Psolution (actual).

Step-by-step explanation:

Number of moles of CS2 = 3.95g/76.13gmol-1 = 0.0519 moles

Number of moles of acetone = 2.43g/58.08gmol-1 = 0.0418 moles

Total number of moles = 0.0937 moles

Mole fraction of CS2 = 0.0519/0.0937 = 0.5538

Mole fraction of acetone = 0.0418/0.0937 = 0.4461

From Raoult’s law;

PCS2 = 0.5538 × 515 torr = 285.207 torr

Pacetone = 0.4461 × 332 torr = 148.1052 torr

Total pressure = 285.207 torr + 148.1052 torr = 433.3 torr