Lecture #2, Wednesday, January 6th

Today I discussed Molar Solubility and started class giving you a list of five compounds and asked which one had the largest molar solubility. This is a very common question you will encounter on my quizzes/exams and it will definitely show up on standardized exams such as the MCAT.

Remember that the solubility of a substance is the quantity that dissolves to form a saturated solution, while the the K_sp is the equilibrium constant established and its magnitude can be used to make predictions about solubility. We can directly relate the solubility of compounds with the same ratio of cation:anion, but if two compounds have a different ratio of cation:anion you must perform a calculation using an ICE table in order to predict which compound is more (or less) soluble.

I then introduced Qualitative Analysis. A qual. scheme is designed to answer the question "What is present?" The "Clueless" episode from the second season of the hit TV show House, which premiered on the FOX network on March 28, 2006, has a "real world" application of the qualitative analysis scheme. House was certain that his patient was being poisoned by a heavy metal toxin. His intuition tells him that this toxin is gold and he sets out to prove that he is right.

He heads back to his house and grabs a vial of stannous chloride and after he applies the solution to the suspects hands it turns purple, confirming gold is present.

In Experiment #25 and #26 you get to act as a "detective" in the same manner House did and will need to identify which cations are present in an unknown sample. You will have four lab periods to identify unknowns from Group I, II, and III.

I will do my best to explain the fundamental concepts in this lab and relate them to solubility. For instance, Ag⁺ and Pb²⁺ are both contained in group I, but Pb²⁺ is also present in trace amounts in Group II, but Ag⁺ never is. The reagent used to isolate the Ag⁺ and Pb²⁺ ions from the other cations is cold, dilute HCl. I did a calculation relating the K_sp to the molar solubility then calculated the amount of AgCl and PbCl₂ that will dissolve in 4 mL of water.

I will start class on Friday discussing the criteria or the concentrations of each ion needed to form a precipitate in solution. We will then continue with the Group II concepts and factors that influence solubility.

Songs played before class:
Journey: Don't Stop Believing
DJ Earworm: United State of Pop 2009 - Mashup of Top 25 Billboard Hits