Question

The vapor pressure of benzene is 73.03 mm Hg at 25 °C. A nonvolatile, nonelectrolyte that dissolves in benzene is TNT.  

Calculate the vapor pressure of the solution at 25 °C when 14.83 grams of TNT, C₇H₅N₃O₆ (227.1 g/mol), are dissolved in 254.5 grams of benzene.

benzene = C₆H₆ = 78.12 g/mol.

VP(solution) =-________mm Hg?

Answer 1

no of moles of TNT nTNT = 14.83/227.1   = 0.0653 moles

no of moles of benzene nB = 254.5/78.12   = 3.26 moles

from roult's relative lowering of vapor pressure is equalt of mole fraction of solute

P0 -Ps/P0    = ns/ns + no

P0 -Ps/P0    = ns/ no               no of moles of solute isvery less compared to solvent no>>ns

73.03-Ps/73.03   =      0.0653/3.26

(73.03-Ps) 3.26 = 0.0653                

Ps = 73 mmHg             

vapor pressure of solution is 73mmHg