If a volatile solute is added to a volatile solvent, both substances contribute

Question

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 (CGHsCHa) and 2.0 mol of benzene (CsHø) 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? 2.

Explanation / Answer

from daltons law

Ptotal = Ptoluene + pbenzene

         = Xtoluene*P0toluene + Xbenzene *P0benzene

Xtoluene = ntoluene/ntotal

         = 1/(2+1)
      
         = 0.333

P0toluene = 22 mmhg

Xbenzene = 2/3 = 0.667

P0benzene = 75 mmhg

Ptotal = 0.333*22 + 0.667*75

         = 57.35 mmhg

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