Question

PART A If 0.480 mol of a nonvolatile nonelectrolyte are dissolved in 3.60 mol of water, what is the vapor pressure PH2O of the resulting solution? The vapor pressure of pure water is 23.8 torr at 25 ∘C . Express your answer with the appropriate units.

PART B A solution is composed of 1.90 mol cyclohexane (P∘cy=97.6 torr) and 2.30 mol acetone (P∘ac=229.5 torr). What is the total vapor pressure Ptotal above this solution?

Answer 1

PART A If 0.480 mol of a nonvolatile nonelectrolyte are dissolved in 3.60 mol of water, what is the vapor pressure PH2O of the resulting solution? The vapor pressure of pure water is 23.8 torr at 25 ∘C . Express your answer with the appropriate units.

Addition of nonvolatile component decreases the vapor pressure.

Moles of component = 0.48 mol, moles of water= 4.6

mole fraction of water= moles of water/total moles =4.6/(4.6+0.48)= 0.91

Vapor pressure of solution = pure component vapor pressure* mole fraction of water in solution= 23.8*0.91

=21.65 Torr

2. moles of cyclohexane (n1)= 1.90 moles. moles of acetone= 2.3, mole fractions = moles of component/total moles

mole fractions :Cyclohexane, x1= 1.9/(1.9+2.3)= 0.45, acetone,x2= 1-0.45=0.55

pressure of solution, P =x1P1sat+x2P2sat, P1sat and P2 sat are saturation pressures of cyclohexane and acetone respectively. P =total pressure, P=0.45*97.6+0.55*229.5 = 170.145 Torr