Question

The boiling point of an aqueous solution is elevated by 0.15 degrees celcius. the change in freezing point of the solution, delta T, is?
a.) -6.32
b.) 0.15
c.) -0.15
d.) 0.54
e.) -0.54
I know the answer is d, i just don't understand how to get it! thanks!

Answer 1

Note the correct spelling of celsius.
delta T = Kb*molality
solve for molality
0.15 = 0.512*m and
m = 0.15/0.512

Then substitute molality into the freezing point depression equation.
delta T = Kf*m
delta T = 1.86*(0.15/0.512)
delta T = 0.5449 which rounds to 0.54 to two significant figures.