Question

The freezing point of water H2O is 0.00°C at 1 atmosphere. A nonvolatile, nonelectrolyte that dissolves in water is antifreeze (ethylene glycol).

How many grams of antifreeze, CH2OHCH2OH (62.10 g/mol), must be dissolved in 297.0 grams of water to reduce the freezing point by 0.400°C ?

_____ g antifreeze.

Answer 1

delta T = Kf * molality

where, delta T = depression in freezing point

0.400 = 1.86*molality

molality = 0.400 / 1.86 = 0.215 m

molality = number of moles of solute / mass of solution in kg

0.215 m = number of moles of solute / 0.297 kg

number of moles of solute = 0.215 * 0.297 = 0.0639 mole

number of moles of solute = mass of solute /molar mass of solute

0.0639 = mass of solute / 62.10 g.mol^-1

mass of solute = 0.0639 * 62.10 = 3.97 g

Therefore, the mass of antifreeze added must be 3.97 g