A Reading Guide and Homework List for Chapters 16

October 26 - November 2

Chapter 16

• 16.1 — The important concept here is that of the titration reaction and the cell reaction. Carefully review the boldface information, blue box and sidebar notes on page 417. The fact that the cell voltage can be described in either of two ways is a key factor in evaluating the shape of a redox titration curve, since one way works best before the equivalence point and the other works best after the equivalence point. The choice of which reaction to use will be determined by the information that is available about the titrant or reactant species. Before the equivalence point it will be best to use the half-reaction for the analyte species to determine cell potential, since concentrations of both the oxidized and reduced forms can be easily calculated from the stoichiometry of the balanced equation. After the equivalence point the half-reactions for the titrant species are used to calculate the cell potential, since it is now easy to calculate the concentrations of these oxidized and reduced species from the stoichiometry of the balanced equation. These concepts are reinforced by the sidebar comments for the example that is given on pages 418 and 419. I'll work a different example in class so you can start to see this process applied to other reactions.
  
  The potential at the equivalence point receives special consideration. Again, this is given by the example in the book and will be described by a different example in class. Once you understand the process of this calculation it can be applied to any titration situation.

• 16.2 — This is the same general concept of indicators that occurs for acid-base or complex formation. Namely, that the relative ratio of two different species changes quickly and significantly when a certain property of the solution undergoes a change at the equivalence point. To be a successful indicator the value of the solution property that changes must be associated with a property of the indicator. In acid-base titrations the solution pH is associated with the K_a of the indicator, in complex titrations the p(metal ion) is associated with the K_f of the ligand that is used as a titrant and in redox titrations the E_cell at the equivalence point is associated with the E° for the indicator. The main skill here is calculating the cell potential at the equivalence point, since once this is determined the process of selecting an appropriate indicator is simply a matter of looking at a table. A few of the homework problems deal with this issue.

• 16.3 — These are specific applications of selected redox reactions. Anything here would be based on the appropriate half-reaction from the standard reduction table. If you are given any specific equation you should be able to determine a balanced reaction for any given application. So, if you can handle the general process of dealing with balanced redox reactions you can handle any of these specific applications. You might note that you have already used the persulfate digestion in the phosphorous lab (remember why) and observed the spontaneous disproportionation of hydrogen peroxide as the genie in the bottle.

• 16.4 — 16. 7 — Again, these are all specific applications of redox reactions. If you can combine any two standard reduction half-reactions to yield a balanced spontaneous reaction, you have the skills to deal with any of these reagents as titrants. Because of the differences in their reduction potentials and the conditions under which they may be successfully applied (such as acidic or basic), they each have applications for which they are preferred. You don't need to be able to list the various applications, but if you are given one you should be able to describe the analytical reaction of interest , the shape of the redox curve or recommend an appropriate indicator. Also, a few of the homework problems look at the stoichiometry of several redox titrations and their application in back titrations. Don't try to memorize all the different reactions, rather focus on the concept that all of these applications simply involve a reduction and an oxidation and that the reaction (or cell) potential can always be described by the consistent application of the Nernst equation to the individual half-cells..
  
  Since the use of the starch-iodine complex is so common, you should be aware of what is happening in this situation (page 424 and 431). You should recognize the names of the reagents in each of the headings in these sections, but you will be provided with appropriate information or tables regarding the specific half-reactions for any particular problem that might be given.

Suggested Homework problems - these will not be collected for grading. The answers will be posted in the library by Wednesday, October 28. Concepts demonstrated in these problems are eligible for exam 2 to be given on November 2.

• Chapter 16: 1, 4, 5, 6, 7, 17, 18, 28

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