Answer:
Molar mass X = 18.2 g/mol
Explanation:
Step 1: Data given
Mass of compound X = 231 mg = 0.231 grams
Mass of benzene = 65.0 grams
The freezing point of the solution is measured to be 4.5 °C.
Freezing point of pure benzene = 5.5 °C
The freezing point constant for benzene is 5.12 °C/m
Step 2: Calculate molality
ΔT = i*Kf*m
⇒ΔT = the freezing point depression = 5.5 °C - 4.5 °C = 1.0 °C
⇒i = the Van't hoff factor = 1
⇒Kf = the freezing point depression constant for benzene = 5.12 °C/m
⇒m = the molality = moles X / mass benzene
m = 1.0 / 5.12 °C/m
m = 0.1953 molal
Step 3: Calculate moles X
Moles X = molality * mass benzene
Moles X = 0.1953 molal * 0.065 kg
Moles X = 0.0127 moles
Step 4: Calculate molar mass X
Molar mass X = mass / moles
Molar mass X = 0.231 grams / 0.0127 moles
Molar mass X = 18.2 g/mol
