Question

10. A solution contains 6.50 mol water, 0.300 mol sucrose, and 0.200 mol glucose. The solutes are nonvolatile. What is the vapor pressure of the solution at 35°C given that the vapor pressure of water is 42.2 torr?

35.0 torr d. 39.2 torr

36.0 torr e. 39.0 torr

37.0 torr

11. Indicate which aqueous solution has the fastest evaporation rate.

0.1 M KCl d. 0.1 M MgCl2

0.2 M Na2CO3 e. 0.2 M MgCl2

0.2 M NaCl

12. Identify the following statement as true or false and choose the correct explanation: “For solutions with the same molarity at the same temperature, the pressure needed for reverse osmosis of a sodium chloride solution will always be less than the pressure needed for a calcium chloride solution.”

True, because the molar mass of sodium chloride is smaller.

True, because the van ’t Hoff factor is smaller for sodium chloride.

False, because the van ’t Hoff factor is smaller for sodium chloride.

False, because the van ’t Hoff factor is larger for sodium chloride.

True, because the van ’t Hoff factor is larger for sodium chloride.

Answer 1

10 )

mole fraction of solute = (0.3 + 0.2 ) / (0.2 + 0.3 + 6.5 = 0.07142

Po = 42.2 torr

from raoult's law :

Po - Ps / Po = mole fraction of solute

42.2 - Ps / 42.2 = 0.07142

Ps = 39.2 torr

answer : d ) 39.2 torr

11 )

colligative property = i x m

0.1 m KCl = i x 0.1 m = 2 x 0.1 m KCl = 0.2 m KCl

0.1 m MgCl2 = i x 0.1 m = 3 x 0.1 m MgCl2 = 0.3 m MgCl2

0.2 m Na2CO3 = 3 x 0.2 m = 3 x 0.2 m Na2CO3 = 0.6 m Na2CO3

0.2 m MgCl2 = i x 0.2 m = 3 x 0. 2 m MgCl2 = 0.6 m MgCl2

0.2 m NaCl = i x 0.2 m = 2 x 0.2 m NaCl = 0.4 m NaCl

among all lowest colligative proeprty for 0.1 M KCl so it has highest vapour pressure and evaporation rate

so answer : a ) 0.1 M KCl

12)

answer : True, because the van ’t Hoff factor is smaller for sodium chloride.

explanation :

for NaCl van'thoff factor = 2

for CaCl2 van'thoff factor = 3