Ch 13 - Freezing-point Depression & Boiling-point Elevation

more solute lowers or depresses the freezing point of a solvent (bc it disrupts the orderly crystalline structure that forms when a solvent solidifies)

• Remember: more solute lowers or depresses the freezing point of a solvent (bc it disrupts the orderly crystalline structure that forms when a solvent solidifies)

Change in freezing-point / freezing-point depression (∆Tf)

• Def: amt by which the normal freezing-point will be lowered (NOT the new freezing-point)

• Eqn: ∆Tf = Kf m

constant that is unique for each solvent

• Kf or Kb

Freezing-point of the pure substance

• Tf° or Tsolvent

• memorize the table

5.5 °C

Tf° of Benzene:

5.12°C/m

Kf of Benzene:

80.22 °C

Tf° of Naphthalene:

6.85°C/m

Kf of Naphthalene:

43°C

Tf° of Phenol:

7.40°C/m

Kf of Phenol:

0.00°C

Tf° of water:

1.86°C/m

Kf of water:

more solute raises or elevates the boiling point of a solvent bc it makes it harder for solvent particles to escape from the surface of the liquid

Remember: more solute raises or elevates the boiling point of a solvent bc it makes it harder for solvent particles to escape from the surface of the liquid

Change in Boiling-point / Boiling-point elevation (∆Tb)

• Def: amt by which the normal boiling-point will be increased (NOT the new boiling-point)

• Eqn: ∆Tb = Kb m

Boiling-point of the pure substance

• Tb° or Tsolvent

• memorize the table

80.1°C

Tb° of Benzene:

2.53°C/m

Kb of Benzene:

61.2°C

Tb° of Chloroform:

3.63°C/m

Kb of Chloroform:

100.0°C

Tb° of Water:

0.512°C/m

Kb of Water: