Colligative Properties 

Grading and Lab Submission

• Ensure labs are submitted ASAP to avoid losing credit.

• Grading of routines is coming soon.

Colligative Properties Overview

• Focus on freezing point and boiling point.

• Exam will include:

  • Freezing Point

  • Boiling Point

  • Osmotic Pressure

  • Vapor Pressure

  • Note: Conductivity is not a colligative property.

• Colligative properties are defined as properties that change as solute is added to a solvent.

  • As solute amount increases, changes in boiling and freezing points increase proportionately.

  • Change in properties is gradual with solute addition.

Freezing and Boiling Point Calculation

• Sample values discussed:

  • Freezing Point:

    • Q1: -14°C

    • Q2: -18.6°C

    • Q3: -32°C

    • Q4: -15°C

  • Boiling Points:

    • Q1: 103.9°C

    • Q2: 105.2°C

    • Q3: 108.8°C

    • Q4: 104.2°C

• Notable Points:

  • Ions affect calculations for freezing and boiling points (i-value).

  • Example values and points emphasized for clarity.

Understanding Osmotic Pressure

• Osmotic Pressure (π) relates to concentration and is influenced by the number of particles (ions) from solute.

• Important concepts:

  • Osmosis involves water moving from areas of high concentration to areas of low concentration.

  • Osmotic pressure is the pressure exerted by the water molecules when they pass through a semi-permeable membrane.

• Key Equation:

  • π = i x M x R x T

    • where:

      • π = osmotic pressure

      • i = ionization factor

      • M = molarity

      • R = gas law constant

      • T = temperature in Kelvin

Molarity and Ionization Factors

• Molarity includes units of moles and liters, clarifying the relationship with pressure volume equations.

• Relation to PV = nRT discussed, showing how to rearrange for concentration.

• Ionization factors (i-values) discussed using common examples:

  • Sucrose (not ionizing, i=1)

  • Sodium Chloride (NaCl, dissociates i=2)

  • Calcium Chloride (CaCl2, dissociates i=3)

• Example problems were worked through to reinforce learning.

Exploring Solutions with Dialysis Tubing

• Experiment with dialysis tubing highlighted:

  • Used to demonstrate osmotic pressure and the movement of water through semi-permeable membranes.

  • Defined terms:

    • Hypertonic: higher solute concentration, draws water out.

    • Hypotonic: lower solute concentration, draws water in.

    • Isotonic: equal concentrations of solute.

• Observations of mass changes based on water movement proved key in evaluating osmotic pressure.

Common Ion Effect

• Explanation of how solutes affect solubility and osmotic pressure when present together (common ions).

• Example using sodium chloride and potassium chloride, demonstrating how to calculate concentrations of common ions:

  • Use of mole ratios to figure out the concentration of individual ions in solutions.

  • Practical calculations demonstrated including total ion concentrations using examples from previous lessons.

Conclusion and Homework

• Assigned homework on osmosis, reinforcing the diffusion of water and osmotic pressure calculations.

• Encouraged students to visualize their steps and present data appropriately in lab settings.