Lab 3 - Freezing Point Depression

The Four Colligative Properties (fill in the blanks)

• Osmotic _____

• Lowering of _____________

• Depression of _____________

• Elevation of _______________

• Osmotic pressure

• Lowering of vapor pressure

• Depression of freezing point

• Elevation of boiling point

Molarity (M) is moles of solute divided by the number of _______ of the solution

Liters

Molality (m) is moles of solute divided by the _____ of solvent in ___

Mass in kg

1kg = ________ g

1000

What advantage does Molarity have over Molality?

Molarity is great for measuring exact volumes

What advantage does Molality have over Molarity?

Molality is temperature independent (i.e. concentration does not change with temp.)

ΔTf is the difference between the initial freezing point of the solvent and the _____________

Final freezing point

Kf is the ______________ for the solvent (°C/m)

Freezing point depression constant

m is the concentration (mol solute/kg of solvent) of the solution in _________

Molality

Non-electrolytes do not _______ into “pieces” of the formula units.

Dissociate

Ex: Sugar will dissolve in water but won’t come apart into many pieces.

Sugar (a non-electrolyte) molecules will dissolve in water but will not come apart into many pieces in water. Therefore, one mole of sugar molecules in a solution will yield one mole of __________________.

dissolved sugar molecules

Van’t Hoff Factor (i) is the actual number of particles in solution after dissociation divided by the number of __________ initially dissolved in solution

Formula units

Using the van’t Hoff factor in the calculation accounts for the ____________ that go into solution when ionic compounds dissociate into their constituent cations and anions

multiple moles of ions

Adding a solute to a solvent will

• Decrease the solvent’s __________

• Increase the solvent’s ___________

• Freezing point

• Boiling point

The degree of freezing point depression is related to the identify of the __________, the molar mass of the _______, and the mass of the ________. This relationship is expressed as:

• Identify of the solvent

• Molar mass of the solute

• Mass of the solution

What effect does adding a non-volatile solute to a solvent have on the solvent's freezing point?

a. No change

b. The freezing point increases

c. The freezing point decreases

d. The freezing point remains the same, but the boiling point decreases

The freezing point decreases

Why does the calculated molar mass of an ionic compound tend to be lower than its actual molar mass when using the freezing point depression method?

a. Ionic compounds dissociate into multiple particles in solution.

b. Ionic compounds increase the viscosity of the solution.

c. Ionic compounds do not dissolve in water.

d. Ionic compounds elevate the boiling point too much.

Ionic compounds dissociate into multiple particles in solution.

If 1 mol of a non-electrolyte solute is dissolved in 1 kg of water, causing the freezing point to decrease by 1.86°C, what is the freezing point depression constant (Kf) for water?

a. 1.86°C/m

b. 3.72°C/m

c. 0.5°C/m

d. 2.00°C/m

1.86°C/m

In the experiment, why is it important to stir the ice-water mixture in the polystyrene reaction vessel?

a. To increase the temperature of the mixture

b. To ensure uniform distribution of temperature

c. To prevent the solute from dissolving

d. To decrease the freezing point of water

To ensure uniform distribution of temperature

Which of the following would most likely result in the greatest decrease in freezing point?

a. Dissolving 1 mole of NaCl in 1 kg of water

b. Dissolving 1 mole of sucrose (C12H22O11) in 1 kg of water

c. Dissolving 1 mole of glucose (C6H12O6) in 1 kg of water

d. Dissolving 1 mole of CaCl2 in 1 kg of water (because it dissociates into three ions, Ca2+ and 2 Cl-)

Dissolving 1 mole of CaCl2 in 1 kg of water (because it dissociates into three ions, Ca2+ and 2 Cl-)