Answer:
The molar mass of the unknown non-electrolyte is 64.3 g/mol
Explanation:
Step 1: Data given
Mass of an unknown non-electrolyte = 2.17 grams
Mass of chloroform = 225.0 grams
The freezing point of the resulting solution is –64.2 °C
The freezing point of pure chloroform is – 63.5°C
kf = 4.68°C/m
Step 2: Calculate molality
ΔT = i*kf*m
⇒ ΔT = The freezing point depression = T (pure solvent) − T(solution) = -63.5°C + 64.2 °C = 0.7 °C
⇒i = the van't Hoff factor = non-electrolyte = 1
⇒ kf = the freezing point depression constant = 4.68 °C/m
⇒ m = molality = moles unknown non-electrolyte / mass chloroform
0.7 °C = 1 * 4.68 °C/m * m
m = 0.150 molal
Step 3: Calculate moles unknown non-electrolyte
molality = moles unknown non-electrolyte / mass chloroform
Moles unknown non-electrolyte = 0.150 molal * 0.225 kg
Moles unknown non-electrolyte = 0.03375 moles
Step 4: Calculate molecular mass unknown non-electrolyte
Molar mass = mass / moles
Molar mass = 2.17 grams / 0.03375 moles
Molar mass = 64.3 g/mol
The molar mass of the unknown non-electrolyte is 64.3 g/mol
