Determine the vapor pressure of a solution at 25°C that contains 100 g of naphthalene (C10H8) in 600 g of benzene (C6H6). The vapor pressure of benzene at 25°C is 74.6 torr

Question

Determine the vapor pressure of a solution at 25°C that contains 100 g of naphthalene (C₁₀H₈) in 600 g of benzene (C₆H₆). The vapor pressure of benzene at 25°C is 74.6 torr

Answer 1

Dalton's Law and Raoult's Law

moles C₁₀H₈ = 100 g x 1 mol/128 g = 0.781 moles C₁₀H₈

moles C₆H₆ = 600 g x 1 mol/78 g = 7.69 moles C₆H₆

total moles = 0.781 + 7.69 = 8.47 moles total

mole fraction C₆H₆ = 7.69 mol / 8.47 mol = 0.908 mol fraction C₆H₆

Vapor pressure of solution = mol fraction C₆H₆ x vapor pressure of pure C₆H₆ = 0.908 x 74.6 torr = 67.7 torr