Question

The boiling point of a solution containing 0.5 g of solute B (molar mass 0.128 kg mol^-1) per 50 g of solvent is raised by 0.4 K while 0.6g of another solute C raises the boiling point of 50 g of same solvent by 0.6 K. Calculate molar mass of solute C.

Answer 1

ΔT_f =K_fm

K_f = ?

ΔT=K_f [(W_B)/(M_Bx W_A)]

K_f = (ΔT x M_B x W_A )/ (W_B )
K_f = (0.4 K x 0.128 x 50 g kg mol-1 ) / (0.5 g)
K_{f = 5.12 K kg / mol .}

ΔT_f =K_fm ( for solution c and same solvent )

_{Mc = ?}
ΔT=K_f [(Wc)/( Mc x W_A)]
0.6 K =5.12 [(0.6 g)/( Mc x 50g)]
Mc = (5.12 x 0.6 )/ (0.6 x 50 )
Mc = 0.1024 Kg
_{Mc = 102.4 g}