Liquid A has a vapor pressure of 99.5 torr at 40.0∘C, and liquid B

Question

Liquid A has a vapor pressure of 99.5 torr at 40.0∘C, and liquid B has a vapor pressure of 281 torr at the same temperature. If 7.50 moles of liquid A and 3.00 moles of liquid B are combined to form an ideal solution, what is the vapor pressure above the solution at 40.0∘C?

Answer 1

Dalton's law and Raoult's law.

Total moles = 7.50 moles A + 3.00 moles B = 10.50 moles total

Mole fraction of A = 7.50 moles A / 10.50 moles = 0.714

Mole fraction of B = 3.00 moles B / 10.50 moles = 0-.286

Vapor pressure of A = mole fraction A x vapor pressure of pure A = 0.714 x 99.5 torr = 71.0 torr

Vapor pressure of B = mole fraction B x vapor pressure of pure B = 0.286 x 281 torr = 80.4 torr

Vapor pressure above the solution = 71.0 torr + 80.4 torr = 151 torr