Chapter 18 - Electrolyte Solutions

By Elliott, 3 May, 2018

18.02 Colligative Properties

Colligative Properties

Freezing point depression, boiling point elevation, and osmotic pressure comprise colligative properties. These sample calculations (uakron, 12 min) illustrate how the primary effect of electrolytes is simply to dilute the solvent by a factor proportional to the moles of ions instead of the moles of undissociated molecules.

Comprehension Questions:

1. Estimate the freezing point depression of 10g of KCl in 0.1 L of water.
2. Estimate the osmotic pressure of 60g of CaCl2 in 1L of water.
3. Estimate the boiling point elevation of 150g of NaOH in 1L of water.

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18.09 - Sillen Diagram Solution Method

Sillen Diagram for Electrolyte Calculations (10:14) (msu.edu)

Construction of a Sillien diagram involves several steps that are hard to follow from a textbook. This screencast goes through the steps of solving Example 18.5 from the Elliott and Lira textbook using the Sillen diagram. The problem asks for the pH of a solution that is 0.01 M NaOAc.

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Sillen Diagram for CO2 at fixed partial pressure (9:22)

Sillen Diagram for CO2 at fixed partial pressure (9:22) (msu.edu)

The Sillen diagram lines are quite different compared to a dissolved acid when another phase is present as a 'reservoir'. This can occur in a liquid solution in equilibrium with a gas phase at a fixed partial pressure, or also for a liquid solution saturated with solid.

A template for notes is also provided with many of the equations. Click here.

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Fluconazole Equilibria (7:04) (msu.edu)

Example 18.4 is solved numerically using equations. However, visualization of the equilibria will be helpful in understanding how pH affects the speciation. In this screencast, the Sillen diagram is created. This example demonstrates several useful hints for creating Sillen diagrams.

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