A solution contains naphthalene (C10H8) dissolved in hexane (C6H14) at a concentration of 13.06% naphthalene by mass. Calculate the vapor pressure at 25 ∘C of hexane above the solution. The vapor pressure of pure hexane at 25 ∘C is 151 torr.

The vapor pressure of the solution at is 137 torr

Explanation:

As the relative lowering of vapor pressure is directly proportional to the amount of dissolved solute.

The formula for relative lowering of vapor pressure will be,

where,

= relative lowering in vapor pressure

i = Van'T Hoff factor = 1 (for non electrolytes)

= mole fraction of solute  =

Given : 13.06 g of napthalene is present in 100 g of solution, thus (100-13.06) g = 86.94 g of hexane

moles of solute (napthalene) =

moles of solvent (hexane) =

Total moles = moles of solute (napthalene)  + moles of solvent (hexane) = 0.102 + 1.01 = 1.112

= mole fraction of solute (napthalene) =

Thus the vapor pressure of the solution at is 137 torr

28528289 29823282 8298232 39858