11.3 Colligative Properties

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van’t Hoff factor (i) – number of ions a compound dissociates into per formula unit

-assume strong electrolytes dissociate completely
-a nonelectrolyte has a van’t Hoff factor of 1

Determine the van’t Hoff factor of each of the following:

NaCl

CH3OH

Ba(OH)2

Al(NO3)3

Colligative Properties
Freezing Pt. Depression ΔTF = −iKFm
Boiling Pt. Elevation ΔTB = iKBm
Vapor Pressure Depression (Raoult’s Law)
Osmotic Pressure π= iMRT
Constants for H2O
TF = 0°C KF = 1.86°C/m
TB = 100°C KB = 0.51°C/m
PH2O, 25°C = 24torr

Which of the following aqueous solutions would have the highest boiling point and highest freezing point?

1m NaCl
1m CH3OH
1m Ba(OH)2
1m Al(NO3)3

Which of the following aqueous solutions would have the highest boiling point and highest freezing point?

2m NaCl
1.5m CH3OH
1.2m Ba(OH)2
0.9m Al(NO3)3

What is the freezing point of 1m NaCl in H2O?

What is the boiling point of 1m NaCl in H2O?

What is the vapor pressure of water at 25°C above a solution containing 162g H2O and 32g CH3OH?

What is the osmotic pressure at 25°C in the following diagram?

osmotic pressure