Calculate the molality of a solution containing 8.95 g of ethylene glycol (C2H602) in 560 mg of water.

Question

Ethylene glycol freezes at about -12°C, but when mixed with water, the mixture freezes at a lower temperature. Calculate the molality of a solution containing 8.95 g of ethylene glycol (C2H602) in 560 mg of water.

Answer 1

molality = moles solute / kg solvent

In the example given, C2H6O2 is the solvent and H2O is the solute.

moles of solute = mols H2O = 560 mg x 1 g / 1000 mg x 1 mol / 18 g = 0.03111 mols H2O

kg of C2H6O2 = 8.95 g x 1 kg / 1000 g = 0.00895 kg C2H6O2

Molality = 0.03111 mols / 0.00895 kg

Molality = 3.48 m