Lecture #4, Monday, January 11th

Today's class started with the calculations coming from pages 50 - 52 of the lab manual and it shows us how the Group II and Group III ions are separated.

Be sure to look over these pages of the lab manual and to read the class notes on this material and I want you to know how to:

1. Given a cation, tell whether it will be included in Group II or Group III based on the experimental conditions in Lab #25.

2. If a cation is in Group III, be able to calculate the pH at which its sulfide will precipitate out of solution.

For #1 you will need to know how to calculate Q and then compare it to the K_sp table and for #2 use the method outlined in class today for Fe²⁺ for all the other cations. Homework problems 72 - 79 should be a great help in understanding these concepts.

For pretty much the rest of the week we will investigate the following factors that influence solubility:

1. Common Ion Effect
2. pH
3. Complex Ion Formation
4. Amphoterism

I did a calculation in the notes showing the influence of a common ion and we will extend this to discuss pH effects. You MUST know the strong acids and bases and they can be found here. We will use them to identify if the conjugate of a strong acid/base is acidic, basic, or neutral and equipped with that information we can answer questions as to whether certain reagents will increase, decrease, or have no effect on the solubility of certain slightly soluble salts.

I finished the last 5 min of class by discussing which steps you can skip for the Group III analysis with Ni²⁺, Co²⁺, and Zn²⁺. Remember that your unknown will not contain Zn²⁺ so we can skip quite a few steps. Be sure to look at the conformation tests for Ni²⁺ and Co²⁺ and determine a method for how to identify them.

Lastly, Quiz I given at the beginning of lab this week will include all material up to last Friday's lecture (Lecture #3). This material also includes comparing Q vs. K, which is homework problems 58 - 61 and 63 - 65.

Songs played before class:
Red Hot Chili Peppers - Otherside
Billy Currington - That's How Country Boys Roll