Calculations Involving Colligative Properties Prentice-Hall Chapter 16.4 Dr. Yager

Objectives  Solve problems related to molality and mole fraction of a solution  Describe how freezing-point depression and boiling point elevation are related to molality  Calculate magnitudes of freezing-point depression and boiling point elevation

The Difference molality (m)- new term Molarity (M) - term from 16.2

Key Point Molality and mole fractions are two additional ways in which chemists express the concentration of a solution.

The molality (m) is the number of moles of solute dissolved in 1 kilogram (1000 g) of solvent. Molality is also known as molal concentration.

To make a 0.500m solution of NaCl, use a balance to measure kg of water and add mol (29.3 g) of NaCl.

How many grams of sodium fluoride are needed to prepare a 0.400m NaF solution that contains 750 g of water?

In a solution containing n A mol of solute A and n B mol of solvent B, the mole fraction of solute A (X A ) and the mole fraction of solvent B (X B ) can be expressed as follows:

Mole Fraction can be of Solute or Solvent

Adding Ethlylene Glycol (EG) to water as antifreeze.

A solution contains 50.0g of carbon tetrachloride (CCl 4 ) and 50.0g 0f chloroform (CHCl 3 ). Calculate the mole fraction of each component in the solution.

The magnitudes of the freezing-point depression and the boiling-point elevation of a solution are directly proportional to the molal concentration (m), when the solute is molecular, not ionic. Freezing-Point Depression and Boiling-Point Elevation

The constant, K f, is the molal freezing-point depression constant, which is equal to the change in freezing point for a 1-molal solution of a nonvolatile molecular solute.

The constant, K b, is the molal boiling-point elevation constant, which is equal to the change in boiling point for a 1-molal solution of a nonvolatile molecular solute.

What is the freezing point depression of an aqueous solution of 10.0 g of glucose (C 6 H 12 O 6 ) in 50.0 g H 2 O?

What mass of NaCl would have to be dissolved in kg of water to raise the boiling point by 2.00 o C?

1. What is the mole fraction of He in a gaseous solution containing 4.0 g of He, 6.5 g of Ar, and 10.0 g of Ne? a.0.60 b.1.5 c.0.20 d.0.11

1. What is the mole fraction of He in a gaseous solution containing 4.0 g of He, 6.5 g of Ar, and 10.0 g of Ne? a.0.60 b.1.5 c.0.20 d.0.11

2. The freezing point depression caused by a given concentration of a nonvolatile molecular solute a.depends on the solute. b.depends on the solvent. c.is always the same. d.cannot be determined.

2. The freezing point depression caused by a given concentration of a nonvolatile molecular solute a.depends on the solute. b.depends on the solvent. c.is always the same. d.cannot be determined.

3. What are the freezing and boiling points of a 0.1m solution of CaCl 2 in water? a.-0.2°C, 100.1°C b.-0.6°C, 100.1°C c.-0.6°C, 100.2°C d.-0.6°C, 99.8°C

3. What are the freezing and boiling points of a 0.1m solution of CaCl 2 in water? a.-0.2°C, 100.1°C b.-0.6°C, 100.1°C c.-0.6°C, 100.2°C d.-0.6°C, 99.8°C

4. Compared to the freezing point depression by ethylene glycol (C 2 H 6 O 2,) for a given solvent, the freezing point depression caused by the same molal concentration of CaCl 2 would be a.exactly the same. b.twice as large. c.three times as large. d.four times as large

4. Compared to the freezing point depression by ethylene glycol (C 2 H 6 O 2,) for a given solvent, the freezing point depression caused by the same molal concentration of CaCl 2 would be a.exactly the same. b.twice as large. c.three times as large. d.four times as large