Question

How many grams of ethanol must be added to 500.0 g of water to make a solution that freezes at 0.00 degrees fahrenheit? The molal freezing point depression constant for water is 1.86 degree celsius over moles.

Answer 1

Convert 0 F to C.
C = (F-32)*5/9 = ?
That's approx -17.78
delta T = Kf*m
17.78 = 1.86*m
Solve for molality.
Then m = mol/kg solvent
You have m and kg H2O, solve for mols ethanol.
Finally, mols ethanol = grams/molar mass. You have molar mass and mols, solve for grams.
Post your work if you get stuck.

Answer 2

220 g