AUGUST. 1950
0
A COURSE IN DESCRIPTIVE INORGANIC CHEMISTRY
. IN1945, at the suggestion of Professor E. C. Markham, the Department of Chemistry of the University of North Carolina at Chapel Hill made a careful study of its undergraduate curriculum and concluded that its students were receiving the B.S. degree in Chemistry without an introduction to inorganic chemistry. To remedy this situation, qualitative analysis is offered in the third quarter of the freshman year (the third quarter of general chemistry being omitted), leaving time and laboratory space for the introduction of a new course into the B.S. Chemistry curriculum. The new course is called inorganic chemistry and carries the same prerequisites as does elementary organic chemistry. It is required of all B.S. chemists. Many students take inorganic chemistry simultaneously with a quarter of organic chemistry. Inorganic chemistry is a one-quarter course, meeting three class hours per week and six laboratory hours per week. The subject matter is designed to introduce the student to the chemistry of all of the elements and, as such, does not take the place of the wellkstablished advanced courses in inorganic chemistry. Rather, experience has shown that it permits the advanced courses to be advanced courses in fact, which had not always been the case.
S. YOUNG TYREE, JR. University of North Carolina, Chapel Hill, North Carolina
The laboratory work in inorganic chemistry is largely preparative, with each experiment designed to illustrate a specific technique. As examples: 1. Crystallization. This very fundamental process is emphasised in several experiments, and no single experiment is devised to cover it. 2. High Tempe~atureReactions. ( a ) The reaction between magnesium turnings and elementary nitrogen illustrates high temperature reactions between gases and solids in a protected atmosphere, Ordinary 1-inch iron pipe is used to construct spparatus that services several students a t once from one tank of nitrogen. The student reoeives an expanded picture of the reactivities of these two elements. ( b ) The thermite preparation of iron (or other suitable metal) is an excellent "time-eoanomy" experiment of this type. (c) The reaction between potassium carbonate and titanium dioxide in a platinum crucible is used to illustrate acid-base reactions at elevated temperatures. Two platinum crucibles service a. clam of 30 students. The complexing action of fluoride ion is easily demonstrated on the resulting melt by forming potassium hexafluotitauate. (d) By oxidizing chromite ore to chromate in an alkaline fusion (air as oxidieing agent) the influence of temperature on a chemical reaction is vividly demonstrated. Much chemistry is available in the treatment of the melt to obtain both chromate and dichromate. 3. Reaction i n Nonaoueous Solvents. Easilv demonstrated by the direct synthesis ofdntimony (111) iodide ih benzene. Reflux conditions are demonstrated by this preparation also.
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4. Distillation Phenomena. ( a ) Anhydrous distillations are easily demonstrated in the preparation of tin (IV) chloride or tin (IV) bromide by direct synthesis and purification by distillation. Tin (IV) bromide is somewhat preferable since an air condenser must be substituted for the usual water-cooled condenser. (b) The preparation of antimony (111) chloride by distilling a solution of antimony (111) chloride in concentrated hydrochloric aoid. is used to show much about a three-component system. (c) A modified flash distillation is demonstrated by dropping water on to the magnesium nitride prepared in another experiment, and absorbing the ammonia in water. 5 . Elect~.olyticOzidation. Illustrated in the preparation of potassium peroxydisulfate by the electrolysis of a saturated solution of potassium hydrogen sulfate at 0°C. 6. Tmnsitions in the Solid State. Demonstrated by the preparation of copper ( I ) tetraiodomercurate, which has a fairly sharp transition point at 71DC. 7 . Aeid-Base Phaomena. ( a ) The BrSnsted-Lowry concept is demonstrated in several experiments of an elementary type. (b) The Lewis concept is brought in with the preparation of several coordination compounds. 8. Coordination Compouds. Several of the more easily prepared complexes are offered, e. g., potassium bexachlorostmnate from tin (IV) chloride, potassium trioxalat,xhromate (111) from potassium dichromate, etc. 9. Ion-Ezehange. The separation of two simple ionic species with columns will be an added experiment in the immediate future.
with each chapter of descriptive chemistry. As examples: 1. A comparison of the properties of the chlorides of Mg, Be Al, and B, also the oxides of Mg, Be, Al, and B, is followed by the generalization of the "cross-hatch" similarity observed between the elements in the first two periods. Li Na
Be
B
y~ Mg y~ AI y~
C si
2. The very straight-forward chemistry of the alkalies osn be the basis for the presentation of a modified BornlHaber cycle theory. 3. Under the chemistry of hydrogen, the Bmnsted-Lowry theory of acid-bme reactions as applied to many protonic solvents is presented. 4. The chemistry of tin (with germanium and lead) is an excellent s t a t from which to propound the Lewis acid-base theory. 5. An elementary theory of coordination compounds is presented a t two intervals, namely with the chemistry of group I I B and with the group VIII elements.
The descriptive material presented is not the classical variety. For example: 1. Under the chemistry of silicon, the silanes and the silicones receive more consideration than does silicon dioxide (and ceramics). 2. Hydrogen is likened to the halogens at least as much as it is to the alkalies. Saltlike hydrides are discussed as well as the typical volatile aoid hydrides of the halogens. 3. Hydraeoic acid, hydraeine, and hydraxylemine are presented as being at least as useful and important as t h e several oxides of nitrogen.
The student is required to complete 20 preparations during the quarter, many of which are used in subsequent preparations. The chronological order is not fixed as the apparatus for several experiments is sufficient for a limited number of students at any one time. I n general, the elements used in the laboratory are those disThroughout the course an attempt is made to give cussed in the class, such that the two divisions of the the student some understanding of the nature and course supplement each other. strength of inorganic chemical bonds. The lecture material in inorganic chemistry emphaThe subject of inorganic chemical nomenclature is sizes the periodicity of chemicaland physical properties treated rigorously, as is the use of chemical equations. of the elements. Descriptive chemistry of most. of the Inorganic chemistry is now being taught for the third elements is taught by subgroups. For example, under year. The following generalizations result from experithe chemistry of the IVA elements, the basic chemistry ence with the course thus far: of titanium, zirconium, and hafnium is presented, which 1. Little correlation is observed between the background of includes: 1. Natural occurrence, abundance, and methods of prepara2.
tion. Pronerties of the free elements.
A large portion of class time is spent in the correlation between the observed physical and chemical properties of the elements (and their compounds) and more fundamental properties, such as atomic radii, ionization potentials, ionic radii, electron affinities, charge on the ions. Useful generalizations and theories are included
the student and his succeas in eras~inethe material in the course. Students having had only quakakveanalysis seem to do abour as well a s those having completed two and three years of undergraduate chemistry. 2. Undergradurttes taking the courae are made aware of the scope and importance of inorganic chemistry ttt a propitious time in their chemical training. The knowledge gained is very useful to the students in their subsequent courses.
The Department of Chemistry of the University of North Carolina a t Chapel Hill, feels that this new course is markedly improving the situation with respect to the serious deficiencies in inorganic training of its undergraduate students.
