Colligative Properties Colligative Properties of Solutionsof Solutions

Prentice-Hall Chapter 16.3Prentice-Hall Chapter 16.3Dr. YagerDr. Yager

ObjectivesObjectives

IdentifyIdentify three colligative properties of solutions three colligative properties of solutions

ExplainExplain why the vapor pressure, freezing point, why the vapor pressure, freezing point, and boiling point of a solution differ from those and boiling point of a solution differ from those properties of the pure solvent.properties of the pure solvent.

Colligative PropertyColligative Property

A A colligative propertycolligative property is a property that depends is a property that depends only upon the number of solute particles, and not only upon the number of solute particles, and not upon their identity.upon their identity.

Three important colligative properties of solutions:Three important colligative properties of solutions:

vapor-pressure loweringvapor-pressure lowering

boiling-point elevationboiling-point elevation

freezing-point depressionfreezing-point depression

In a pure solvent, equilibrium is established between the liquid and the vapor, called vapor pressure.

In a solution, nonvolatile solute particles reduce the number of free solvent particles able to escape the liquid. Equilibrium is established at a lower vapor pressure.

3 moles of glucose dissolved in water produce 3 mol of particles. Glucose

does not dissociate. v.p. lowering =

x

3 moles of NaCl dissolved in

water produce 6 mol of particles. NaCl dissociates

into 2 ions. v.p. lowering = 2x

3 moles of CaCl2

dissolved in water produce 9 mol of particles.

CaCl2 dissociates into 3 ions.

v.p. lowering = 3x

Freezing-point depressionFreezing-point depression is the difference in temperature between the freezing point of a solution and the freezing point of the pure solvent.

Key PointKey Point

The magnitude of the freezing-point depression is proportional to the number of solute particles dissolved in the solvent and does not depend upon their identity.

Freezing-Point DepressionFreezing-Point Depression

The freezing-point depression of aqueous solutions makes walks and driveways safer when people sprinkle salt on icy surfaces to make ice melt. The melted ice forms a solution with a lower freezing point than that of pure water.

The wood frog is a remarkable creature because it can survive being frozen. Antarctic fish can also survive freezing water. Scientists believe that a substance in the cells acts as a natural antifreeze, which prevents the cells from freezing.

Boiling-point elevation is the difference in temperature between the boiling point of a solution and the boiling point of the pure solvent.

Key Point

The magnitude of the boiling-point elevation is proportional to the number of solute particles dissolved in the solvent.

Boiling-Point ElevationBoiling-Point Elevation

The boiling point of water increases by 0.512°C for every mole of particles that the solute forms when dissolved in 1000 g of water.

The same antifreeze added to automobile engines to prevent freeze-ups in winter, protects the engine from boiling over in summer.

1.1. Which of the following is NOT a Which of the following is NOT a colligative property of solutions?colligative property of solutions?

a.a. vapor-pressure loweringvapor-pressure lowering

b.b. freezing-point depressionfreezing-point depression

c.c. boiling-point elevationboiling-point elevation

d.d. solubility elevationsolubility elevation

1.1. Which of the following is NOT a Which of the following is NOT a colligative property of solutions?colligative property of solutions?

a.a. vapor-pressure loweringvapor-pressure lowering

b.b. freezing-point depressionfreezing-point depression

c.c. boiling-point elevationboiling-point elevation

d.d. solubility elevationsolubility elevation

2. Choose the correct word for the 2. Choose the correct word for the space: The magnitude of each space: The magnitude of each colligative property of solutions is colligative property of solutions is proportional to the __________ solute proportional to the __________ solute dissolved in the solution.dissolved in the solution.

a.a. type oftype of

b.b. number of particles ofnumber of particles of

c.c. molar volume ofmolar volume of

d.d. particle size of theparticle size of the

2. Choose the correct word for the 2. Choose the correct word for the space: The magnitude of each space: The magnitude of each colligative property of solutions is colligative property of solutions is proportional to the __________ solute proportional to the __________ solute dissolved in the solution.dissolved in the solution.

a.a. type oftype of

b.b. number of particles ofnumber of particles of

c.c. molar volume ofmolar volume of

d.d. particle size of theparticle size of the

3. The decrease in vapor pressure when a 3. The decrease in vapor pressure when a solute is added to a liquid is due tosolute is added to a liquid is due to

a.a. attractive forces between solvent attractive forces between solvent particles.particles.

b.b. repulsion of the solute particles by the repulsion of the solute particles by the solvent particles.solvent particles.

c.c. dissociation of the solvent particles.dissociation of the solvent particles.

d.d. attractive forces between solvent and attractive forces between solvent and solute particles.solute particles.

3. The decrease in vapor pressure when a 3. The decrease in vapor pressure when a solute is added to a liquid is due tosolute is added to a liquid is due to

a.a. attractive forces between solvent attractive forces between solvent particles.particles.

b.b. repulsion of the solute particles by the repulsion of the solute particles by the solvent particles.solvent particles.

c.c. dissociation of the solvent particles.dissociation of the solvent particles.

d.d. attractive forces between solvent and attractive forces between solvent and solute particles.solute particles.

4. You have 500 mL of 14. You have 500 mL of 1MM solutions of solutions of NaCl, NaNaCl, Na22SOSO44, Na, Na33POPO44 and and

AlAl22(SO(SO44))33. Which solution will have . Which solution will have

the highest boiling point?the highest boiling point?

• NaClNaCl((aqaq))

• NaNa22SOSO4(4(aqaq))

• NaNa33POPO4(4(aqaq))

• AlAl22(SO(SO44))3(3(aqaq))

4. You have 500 mL of 14. You have 500 mL of 1MM solutions of solutions of NaCl, NaNaCl, Na22SOSO44, Na, Na33POPO44 and and

AlAl22(SO(SO44))33. Which solution will have . Which solution will have

the highest boiling point?the highest boiling point?

• NaClNaCl((aqaq))

• NaNa22SOSO4(4(aqaq))

• NaNa33POPO4(4(aqaq))

• AlAl22(SO(SO44))3(3(aqaq))