Question

 A solution that contains 4.20 g of X in 200 g of chloroform boils at 62.29⁰C. What is the molecular weight of X?

Answer 1

ΔT = K_bm

m – molal concentration

4.20 / M – moles of X

200 g = 0.2 kg – mass of solvent

So, m = 4.20 / 0.2M

Chloroform boiling point – 61.2⁰С

ΔT = 62.29 – 61.2 = 1.09⁰C

K_b (chloroform) = 3.88

So, 1.09 = 3.88 x 4.20 / 0.2M

M = 74.75 (the molecular weight of X)