A solution of toluene in 401 g of cyclohexane has a boiling point of 90.3 °C. How many moles of toluene are in the solution? (For cyclohexane Kb = 2.92 °C/m, Tb = 80.9 °C)

There are 1.29 moles of toluene in the solution.

Explanation:

m = ∆Tb/Kb

m is molality of the solution

∆Tb is the change in boiling point of cyclohexane = 90.3 ° C - 80.9 °C = 9.4 °C

Kb is the boiling point elevation constant of cyclohexane = 2.92 °C/m

m = 9.4/2.92 = 3.22 mol/kg

Number of moles of toluene = molality × mass of cyclohexane in kilogram = 3.22 × 401/1000 = 1.29 moles