Pure solvent has a freezing point 16 5 deg c On dissolving 0 4 gm of B in 200 - Chemistry - Solutions

Question

Pure solvent has a freezing point 16 5 deg c On dissolving 0 4 gm
of B in 200 g of A, the solution freezes at 16 4 deg c and on
dissolving 2 24 g of C in 100 g of A, the soln has a freezing pt of
16 0 deg c If the molecular wt of B is 74, what is the molecular wt
of C?

Geetha · Accepted Answer

Depression in freezing point is,∆Tf = Kf × mTf - Tf(s) = Kf × W2M2 × W1 × 1000Tf - freezing point of pure solventTf(s) - freezing point of solutionW2 - weight of the solute in gW1 - weight of the solvent in gM2 - molecular weight of the soluteFor B in ATf - Tf(s) = Kf × W2M2 × W1 × 100016
5 - 16 4 = Kf × 0
474 × 200 × 1000Kf = 0
1 × 74 × 2000
4 × 1000 = 3 7 K  kg/mol
For C in ATf - Tf(s) = Kf × W2M2 × W1 × 100016
5 - 16 = 3 7 × 2
24M2 × 100 × 1000M2 = 3
7 × 2 240
5 × 100 × 1000 = 165
76 gThus the molecular mass of the solute C is 165
76 g

Pure solvent has a freezing point 16.5 deg c. On dissolving 0.4 gm of B in 200 g of A, the solution freezes at 16. 4 deg c and on dissolving 2.24 g of C in 100 g of A, the soln has a freezing pt of 16.0 deg c . If the molecular wt of B is 74, what is the molecular wt of C?