Calculate the freezing point..?

Question

Calculate the freezing point of 12.40 g of urea (NH2)2CO are dissolved in 99.53 g of benzene. The Kf for benzene is 5.12 C/m. Pure benzene freezes at 5.48 C.

Answer 1

Moles urea = 12.40 g/ 60.0558 g/mol =0.2065

m = 0.2065 / 0.09953 Kg =2.075

delta T = 5.12 x 2.075 =10.62

f.p. = 5.48 - 10.62 = - 5.14 °C