Today I started off by quickly reviewing the example problem given at the end of lecture on Friday and then looked at the Ksp of Cadmium Hydroxide and discussed why we might see different reported Ksp for this substance.
We then skipped ahead to Section 17.6 in the text, which allows us to calculate if a precipitate will form when two (or more) solutions of known concentrations are added together. I performed two examples based on this concept and chemists can use these principles to separate or remove a desired ion from a solution containing many other ions.
We can selectively separate ions in solution by manipulating the concentrations of precipitating agents that are mixed together. The reaction quotient, Q, is obtained when concentrations of reactants are inserted into an equilibrium expression. If we are at equilibrium we have a special case of Q that we refer to as K. I performed an example of Q vs. K by analyzing solutions of silver nitrate and potassium chloride.
If you are asked to predict if a precipitate will form you need to calculate Q and compare it to K. In general, if:
Q < K no precipitate forms
Q = K the solution is at equilibrium
Q > K a precipitate will form
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 spend three lab periods analyzing the known solution and you will have one lab period to identify unknown cations present in your sample. The sole part of your grade will depend on if you properly identify the ions in your unknown solution.
I will do my best to explain the fundamental concepts in this lab and relate them to solubility.
If you are keeping up with the material so far you should be able to complete problems 1-18 and 58-63 on the homework set posted on Carmen. I would encourage you to work out the problems first without looking at the worked out solutions, then checking the key to be sure your work is complete.
Today's inspirational quote was submitted by Dina Yacoub
"Take the first step in faith. You don't have to see the whole staircase, just take the first step."
Martin Luther King, Jr.
Song Played Before Class:
Kanye West ft. Dwele - Power
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