Calculation of Freezing Point

Question

Ethylene glycol (C2H6O2) is used as an antifreeze in cars. 400 g of ethylene glycol is added to 4.00 kg of water. Calculate how much the freezing point of water will be lowered. The freezing-point depression constant for water is Kf = –1.86°C/m.

Answer 1

For calculating the freezing point depression we use ∆T = imk

∆T = change in temperature = ?

i = vant Hoff factor = 1 for ethylene glycol (a non electrolyte)

m = molality = moles solute/kg solvent = 400 g/62 g/mol /4.00 kg = 1.61 m

K = -1.86º/m

∆T = (1)(1.61)(-1.86) = -3.00 deg (this is how much the freezing point will be lowered)