How many grams of Urea would you have to dissolve in 500ml of H2O in order for the mass percent of H2O to be 88.8%? What is the mole fraction of Urea? What are the new boiling and freezing points?

Answer 1

88.8% urea means 88.8g urea/100 g soln.
I would set up
[xgrams urea/(500g H2O + x g urea)] = 0.888
Solve for x to obtain grams urea needed.
moles fraction = moles urea/total moles.

Plug this information into
delta T = Kf*m and
delta T = Kb*m. You will need to convert mass percent to molality.