4. Ethylene glycol (C2H6O2) is used as an antifreeze in cars. If 400 g of ethylene glycol is added to 4.00 kg of water, what is the molality? Calculate how much the freezing point of water will be lowered. The freezing-point depression constant for water is Kf = –1.86°C/m. Show your work.
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ok, so first calculate the molality which is just moles solute/kg solvent... to get the moles solute, you just divide the grams of ethylene glycol by its molecular weight. to obtain the freezing point depression, use the eqn deltaTf = (molality)(Kf).... basically, just multiply the molality you computed to the given Kf...
molar mass of ethylene glycol = 62g
mass of ethylene glycol = 400g
mass of solvent (in kg) = 4kg
molality = \[400/(62*4)\]
delta Tf = Kf * m
= -1.81 * 1.61
= -2.99 C