Answer
11kg
Work Step by Step
(change in) T = - K(f) x m
Convert -12 degrees F to degrees C:
(-12 - 32) x (5 / 9) = -24.4 degrees C
(change in) T = -24.4 - 0 = -24.4 degrees C [remember 0 is the normal freezing point of water]
K(f) = 1.86 degrees C / molality [can be found on freezing point depression chart]
Since you have T and K(f) solve for m:
m = (-24.4 degrees C) / ( -1.86 degrees C / m)
m =13.118 mol C2H6O2 / 1 kg water
This number is per 1 kg of water, since we have 14.5kg we multiply by 14.5
13.118 mol C2H6O2/ 1 kg x 14.5 kg = 190.211 mol C2H6O2 needed
convert mol to grams
190.211 mol x (62.08 g / mol) = 11808.298 g or 11.808 kg
