1-A 0.511 g sample of a nonvolatile, yellow crystalline solid dissolves in 13.0

Question

1-A 0.511 g sample of a nonvolatile, yellow crystalline solid dissolves in 13.0 g of benzene, producing a solution that freezes at 5.39 oC. Find the molar mass of the yellow solid. The following may be useful: The freezing point of benzene is 5.51 oC and the freezing point depression constant, kf, is 4.90 oC/m.

2-A 8.70% solution by mass of an enzyme in water has an osmotic pressure of 14.2 torr at 294 K. Calculate the molar mass of this enzyme. (Assume that the density of the solution is 1.00 g/mL.)

3-A saline solution contains 6.3 g of NaCl in 1.00 kg of water. Assuming an ideal value for the Van't Hoff factor, i, calculate the freezing point of this solution in oC.

Explanation / Answer

t = i Kf m

Pure benzene freezes at 5.51 °C

t = 5.51 -5.39 = 0.12

0.12 °C = (1) (4.9°C kg mol-1) (x / 0.013 kg)

X = 3.183 x 10-4 Mol

Molar mass of the compound = 0.511 g/ 3.183 x 10-4 mol = 1605 gm/mol

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