Today's class started with me performing a calculation to determine if a particular precipitate will form when you are given the concentrations and volumes of various reagents. Remember that Q can be any concentration you want it to be, and the K, or Ksp, is the concentrations at equilibrium.
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 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. Be sure to read pages 35-37 of the lab manual as it describes how the ions are separated into groups. These grouping are based on solubility, and as I showed in class, to a first approximation we can use the Ksp table to see which ions will precipitate when we add a particular reagent.
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 Ksp to the molar solubility then calculated the amount of AgCl and PbCl2 that will dissolve in 4 mL of water.
We will discuss more on the experimental conditions of Exp. #25 Group I and introduce the concept of complex ion to start on Monday.
Over the weekend you should be sure to have the Ksp report question quiz finished by 10:00 pm tonight and you should work on the pre-lab for Exp #25.
If you have been keeping up with the material, you should have read sections 17.4, 17.6, 17.7 and you should be able to handle homework questions 1-18, 19-23, and 58-71.
I hope everyone has a Happy Easter!
Songs played before class:
Kenny Chesney - Summertime
Jay Sean - Down (ft. Lil Wayne)
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