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# Concentration Units

By Tommy Reed,2014-12-03 16:53
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Concentration Units

Chem 125 Spring 2011 Dr. Neff

Colligative Properties

1. Ethylene glycol (HOCHCHOH) is a common additive to the water in a car’s radiator. 22

a) What is the freezing point of radiator fluid prepared by mixing 1.00 L of ethylene glycol

with 1.00 L of water? The density of ethylene glycol is 1.114 g/mL; the density of water

is 1.000 g/mL; and the freezing point depression constant of water, K, is 1.86?c/m. f

b) What is the boiling point of the radiator fluid described above? The boiling point

elevation constant, K of water is 0.52?C/m. b

?2. When crude oil is pumped out of the ground it may be accompanied by formation water that

contains high concentrations of NaCl. If the boiling point of a sample of formation water is

2.3?C above the boiling point of pure water, what is the molality of particles in the sample?

Assume an ideal van’t Hoff factor for NaCl.

?Formation water is water that naturally occurs within the pores of rock.

3. Which of the following aqueous solutions should have the highest boiling point: 0.50 m

glucose, 0.50 m chloride or 0.50 m calcium chloride?

4. The following data were collected for three compounds in aqueous solutions. Determine the

value of the van’t Hoff factor for each salt (K for water is 1.86?C/m): f

Compound Concentration Observed ;Tf (?C)

Lithium chloride 5.0 g/kg 0.410

Hydrogen chloride 5.0 g/kg 0.486

(hydrochloric acid)

Sodium chloride 5.0 g/kg 0.299

5. The following pairs of aqueous solutions are separated by a semipermeable membrane. In

which direction will the solvent flow?

a) A = 1.25 M sodium chloride; B = 1.50 M potassium chloride

b) A = 3.45 M calcium chloride; B = 3.45 M sodium bromide

c) A = 4.68 M glucose; B = 3.00 M sodium chloride

6. Calculate the osmotic pressure across a semipermeable membrane separating pure water

from seawater at 25?C. The sum of the concentrations of all the ions in seawater is 1.14 M,

assume that this concentration already takes into account the van’t Hoff factor.

7. 100.0 mL of a solution of physiological saline (0.92% sodium chloride by mass) is diluted by

the addition of 250.0 mL of water. What is the osmotic pressure of the final solution at 37?C?

Assume that sodium chloride dissociates completely in this solution. Also assume a density

for the solution of 1.0 g/mL

Chem 125 Spring 2011 Dr. Neff

8. The freezing point of a solution prepared by dissolved 150 mg of caffeine in 10.0 g of camphor

is lower by 3.07?C than that of pure camphor (K = 39.7?C/m for camphor). What is the molar f

mass of caffeine?

9. A 188 mg sample of a nonelectrolyte isolated from throat lozenges was dissolved in enough

water to make 10.0 mL of solution at 25?C. The osmotic pressure of the resulting solution was

4.89 atm. Calculate the molar mass of this compound.

10. Calcium chloride is often used to melt ice on sidewalks. Could calcium chloride melt ice at -

20.0?C? Assume that the solubility of calcium chloride at this temperature is 70.1 g calcium

chloride per 100.0 g water and that the van’t Hoff factor for a saturated solution of calcium

chloride is 2.5. (I’ve used this problem on past exams)

11. A mixture of table salt and ice is sued to chill the contents of hand-operated ice cream makers.

What is the melting point of a mixture of 2.00 lb of sodium chloride and 12.00 lb of ice if exactly

half the ice melts? Assume that all the sodium chloride dissolves in the melted ice and that

the van’t Hoff factor for the resulting solution is 1.44

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