What is the vapor pressure (in torr) of an aspririn solution at 85 °C, if the solution contains 872.3 g of aspirin (C9H8O4, 180.16 g/mol) in 719.3 mL of water.

Question

The vapor pressure of pure water at 85°C is 433 torr and the density is 0.969 g/mL.

 

Enter your value with 3 significant figures

Answer 1

Find moles of aspirin and moles of water.

Find the mole fraction of water.

Find the vapor pressure.

moles aspirin = 872.3 g x 1 mol/180.16 g = 4.842 moles

moles water = 719.3 ml x 0.969 g / ml x 1 mol / 18 g = 38.72 moles

Total moles = 4.842 + 38.72 = 43.56 moles

mole fraction of water = 38.72 moles / 43.56 moles = 0.8889

Vapor pressure of water = 0.8889 x 433 torr = 385 torr