AUGUST, 1950
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INORGANIC CHEMISTRY AT THE UNIVERSITY OF CALIFORNIA WENDELL M. LATIMER University of California, Berkeley, California
1AM GLAD to take part in this symposium which deals changed to a class discussion at any time by the instrucwith instruct,ion in inorganic chemistry, largely because tor stepping to the blackboard. i t affords me an opportunity to give credit to the late The course aims to teach the general principles of inProfessor William C. Bray for his contributions in this organic chemistry as outlined in the Hildebrand text field. You may recall that Don Yost dedicated his and by the end of the year to get the student to the volume on "Systematic Inorganic Chemistry" to Pro- point where he can read the literature of inorganic fessor Bray and I, too, would like to dedicate my re- chemistry as presented in the Latimer and Hildehrand marks to him since it was largely his philosophy which "Reference Book." The laboratory work is a carefully had guided the development of inorganic chemistry at planned sequence of experiments which are designed to give an understanding of chemical equilibrium and the ~erkile~. Professor Bray believed that the freshman course principles of qualitative analysis. Professor Bray was should be built around the laboratorv work and that one of the leaders in the development of formal schemes this work should be carried out in highly supervised of qualitative analysis, as for example, the Noyes and study sections. With this in mind he designed our Bray "Analysis for the Rare Elements." In spite of freshman chemistry building with its many small this, Professor Bray was opposed to teaching formal rooms, each providing laboratory space for twenty-five qualitative analysis. He held that the students should students. Each room has one or, frequently, two in- be taught those principles which enabled him to destructors, and the laboratory work of the section may be velop methods of analysis. We hope that a t the end of
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the freshman year our students will be able to use not merely a scheme of analysis but any scheme of analysis. In the first term of our second year we give an introductory course in quantitative analysis which stresses the general basic techniques of quantitative determinations. This is followed by a term of advanced quantitative where the student receives more drill in "end-point determinations," but where the emphasis is on methods of quantitative separations. For this work we believe that the Swift "A System of Chemical Analysis" is in a class by itself. If you wish to know just how good your students are as analysts give them a tough alloy with many elements and see what they can do. My guess is that they will end up using the Swift "System." Fmally, in the inorganic analytical field, we offer a course in micro and ultramicro techniques given by Dr. Cunningham of Professor Seaborg's group. We regard this training as especially important for students who expect to work in radioactive or so-called "nuclear chemistry." Our most important upper division advanced inorganic course is the one developed by Professor Bray in the field of reaction kinetics and now given by Dr. Connick and Dr. Powell. This course is characterized by Bray's meticulous insistance on attention to details. For every reaction he asked the questions: (1) What is the main reaction? (2) Are there side reactions? (3) What is the nature of the equilibrium state? (4) What can be said of the rate of the reaction? (5) If the rate is measurable, what is the rate law for the reaction? (6) Finally, what mechanism will account for the rate law for the reaction? The student learns to answer these questions by planning and interpreting experiments in the laboratory. Examples of reactions studied are: the oxidation of iodide by iodate and hydrogen peroxide, the catalytic decomposition of hydrogen peroxide by the bromidebromine couple, the decomposition of nitrous acid, the reduction of nitrous acid by ferrous ion, and the reduction of hydroxylamine by zinc. I do not know of an equivalent course given anywhere in the country, and I regard it as the most essential factor in our training in inorganic chemistry. Our other advanced inorganic course is a lecture course which I give and for which I wrote the "Oxidation Potentials" as a text. It stresses the thermodynamical interpretation of inorganic data. I call it a parlor conversation course in chemistry since I strive to fix in the student's mind those facts which will enable them to discuss intelligently the chemistry of any element. As a minimum requirement a student should know the oxidation states of each element; and for each state, he should know the formulas of the simple and complex ions, something of the acidic and basic nature of the state, and a t least a qualitative idea of the potentials required to oxidize or reduce the state. For example, if one knows that the formula of pervanadyl is V(OH)4+ and that with alkali it forms hewanadate HzV,O,,-- and that in acid solution, the pervanadyl is an oxidizing agent about like bromine, then, I believe, he
JOURNAL OF CHEMICAL EDUCATION
can a t least talk intelligently . about the +5 state of vanadium. I use my system of potential diagrams, which I introduced in "Oxidation Potentials" to correlatea vast number of reactions. As an example of the use of such diagrams, I will discuss the case of neptunium for which we have the following formal potentials in 1M HC1
It will be noted that the potentials become progressively more negative from left to right. This means that the +3, +4, and +5 states are all stable with respect to disproportionation. The least stable is the +5 state, but even here the reaction has 0.4 volt against it, and will not occur appreciably unless there is present some agent which complexes preferentially with the +4 or +6 state. This is true of sulfate ion, and a disproportionation equilibrium is set up in sulfuric acid solutions. The N ~ - N P +potential ~ is highly positive, so the metal will dissolve in hydrochloric acid, but the reaction will stop a t N P + ~since the R T P + ~ - N ~couple +~ is negative. From the value of this last couple, -0.14, one can predict that oxygen of the air will oxidize Np+* rapidly, i. e., the HzOrOz couple is a rapid oxidizing agent up to -0.6 volt. By the same reasoning one can predict that oxygen of the air will not readily oxidize NP+~ to Np02+ or NpOz++. Since the intermediate states are stable, the over-all potentials such as Np+3NpOz+-0.44 are not significant. One can also state that hot concentrated nitric acid, which is about like Clz in potential, will oxidize the metal to NpOz++ going through each of the intermediate states. One would also be confident that NpOz++ in 6 N HCl would slowly evolve Clz. The potential is only slightly unfavorable and the volatility of Clz will allow the reaction to proceed. I could continue this type of correlation a t considerable length, but this is sufficient to illustrate my point. However, it is also of interest to note predictions which can be made with regard to reaction rates. The Np+sNp+&andthe NpOz+-NpOz++ couples should be readily reversible since they involveonly the transfer of single electrons. On the other hand it may be pred.icted that the N P + ~ N ~ O couple ~ + is not reversible, as considerable energy will be required to break the Np-0 bonds. I believe that this type of course has considerable value in that it gives the student a framework on which he can continue to hang additional facts for the rest of his life. However, it is no substitute for the laboratory approach developed by Professor Bray, and if a student must choose between the two courses I certainly recommend the laboratory work as the more valuable. This concludes my summation on the positive side for our department. On the negative side, we give no organized work ih inorganic preparation, although we do have a few students each term doing special problems
AUGUST, 1950
in this field. I regard this as unfortunate. In my early days I took a course in inorganic preparations from Professor Harkins a t Chicago, and I have always regarded this training as highly valuable. Also, I believe that Professor Schlesinger a t the University of Chicago has made one of the few major contributions to inorganic
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chemistry of the past fifty years in his work on the chemistry of boron. On the other hand, when it came to working out the chemistry of plutonium in a short time, I think that the performance of the boys with our Berkeley thermodynamic reaction-kinetic training was a real tribute to the philosophy of William C. Bray.
