A solution is made by adding 50.0 mL of ethanol (C₂H₅OH, d = 0.789 g/mL) to 50.0 mL of water (d = 0.998 g/mL). What is the total vapor pressure over the solution at 20°C? (See Study Question 75.) The vapor pressure of ethanol at 20°C is 43.6 mm Hg.

Data given in Question 75

If a volatile solute is added to a volatile solvent, both substances contribute to the vapor pressure over the solution. Assuming an ideal solution, the vapor pressure of each is given by Raoult’s law, and the total vapor pressure is the sum of the vapor pressures for each component. A solution, assumed to be ideal, is made from 1.0 mol of toluene (C₆H₅CH₃) and 2.0 mol of benzene (C₆H₆). The vapor pressures of the pure solvents are 22 mm Hg and 75 mm Hg, respectively, at 20°C. What is the total vapor pressure of the mixture? What is the mole fraction of each component in the liquid and in the vapor?