Ethylene glycol is the main ingredient in the antifreeze that is used in car rad

Question

Ethylene glycol is the main ingredient in the antifreeze that is used in car radiators because it has a low freezing point. What is the molality of a solution that will cause a 9.79 degree C change in the freezing point of water? (Kf of water = 1.86 Kg/mol degree C, i = 1). REPORT YOUR ANSWER TO 2 DECIMAL PLACES. Adding 12.459-g of unknown compound A (i-1) into 0.087-Kg of benzene changes the freezing point of benzene 3.31 degree C below that of the pure solvent. The kf of benzene is 5.12 degree C/moll. What is the molecular weight of the unknown compound? REPORT YOUR ANSWER TO 3 DECIMAL PLACES

Explanation / Answer

3)

delta Tf = Kf x m

9.79 = 1.86 x m

m = 5.26

molality = 5.26 m

4)

delta Tf = Kf x m

3.31 = 5.12 x m

m = 0.646

molality = moles of solute / mass of solvent in kg

0.646 = moles / 0.087

moles = 0.0562

moles = mass / molar mass

0.0562 = 12.459 / molar mass

molar mass = 221.5 g/mol

molecular weight of unknown = 221.5 g/mol

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