AN INTERMEDIATE COURSE IN INORGANIC CHEMISTRY' The Case for Reactions, Syntheses, and Exercises EDWIN S. GOULD Polytechnic Institute of Brooklyn, Brooklyn, New York T o MANY of US coming into recent contact with graduating college chemistry students and with beginning graduate students, it has become apparent that training in inorganic chemistry is often "fractionated" in a somewhat disturbing manner. There is a first short brush with inorganic chemistry as part of beginning general chemistry, but this contact has become progressively shorter as such courses become "modernized" into miniature physical and structural chemistry courses. Then, much later, if the student carries out graduate study, he is sometimes exposed to an advanced course in which the structures of a number of inorganic compounds are discussed in detail from the modern point of view, together with detailed and rigorous descriptions of the newer methods of structural investigation, but with little emphasis on reactions. I n short, students are learning more and more about what inorganic substances are but less and less about what they do. Well-trained students are justifiably expected to have some proficiency in elementary organic chemistry; they should be able t o devise reasonable synthetic methods, to predict reactions of simple organic compounds, to name compounds properly, and to interpret organic analytical data; and they should know something of stereochemistry. All too often, however, the corresponding "know-haws" in the field of inorganic chemistry are absent. A student who knows how chromyl chloride will react with a-methylnaphthalene mill be unable to guess how chromyl chloride reacts with the much more common reagent, water. He can perhaps suggest a synthesis of benzyl alcohol using lithium aluminum hydride, but he will often be unable to make lithium aluminum hydride. The better students know how selenium dioxide reacts with cyclohexanone and how titanium(II1) chloride reacts with azobeuzene, but generally they are at a loss to predict how selenium dioxide reacts with hydriodic acid or how titanium(II1) chloride reacts with nitric acid. Even after an advanced inorganic course, there are apt to be disturbing gaps in students' knowledge. Nany can write the resonance forms for hydrazoic acid
and discard the form with "unfavorable distribution of formal charge," but few know how to synthesize this compound or how the compound reacts with hydrogen sulfide. Many can predict the dipole moment of boron(II1) fluoride, but few can guess correctly how it will react with hydrazine. Some can calculate the molar paramagnetic susceptibility of K$e(CN)6, but few can devise a synthesis of this compound from Fea04. In an attempt to close this type of "inorganic gap," a number of schools now offer "intermediate" or "advanced" inorganic courses to juniors or seniors. Idcall?.,swh :I ~~ourwshonld prtwnt .som~~of the m(xltm theorrtic~lidem at a Ic\,elItt\v enongh to ennl,le students having only a moderately good background in college mathematics and physics to appreciate the applicability and limitations of the more recent concepts. Obviously, a student gradua.ting in chemistry today should know something about atomic energy levels, newer acid-base interpretations, bond energies, electronegativities, bond lengths and interbond angles, dipole moments, magnetochemistry, molecular spectra, X-ray crystallography, and nuclear reactions. However, each of these topics is likely to receive more detailed treatment in other courses, and it might well be argued that the chief function of the intermediate inorganic course is to extend and strengthen the student's knowledge of reaction chemistry, using recent interpretations where feasible. In the experience of this author, one of the best teaching tools for such a course is a set of challenging (but reasonable) exercises, for one often learns more by "puzzling out" a problem for himself than he learns by reading a textbook or listening to a most lucid lecturer. One of the simplest types of exercise is "the arrangement of items in order" with respect to some property: (1) Arrange the following oxides in order of increasing acidity:
As20., B20s. BaO, BeO, FeO, N,Oa, PnOl, PIOs, CISO,. (2) Arrange these bydrides in order of increasing thermal
stability: HBr, HF, NaH, H20, H2Se, CrtH,, CdH,, SrH,. BZL. (3) ~ r r a n &the following in order of decreasing polariaability: A, Be++, Br-, CI; Li+, Se-2.
1 Presented a t the Meeting-in-Miniature of the Metropolitan Long Island Subsection of the American Chemical Society, February 25, 1955.
The important ability to predict the course of reactions is also developed by suitable exercises: 23
JOURNAL OF CHEMICAL EDUCATION (4) Predict the products in each of the following cases: (a) FeS is treated with aqua regia. (b) Solutions containing the ions Ag(CN)2- and CO(CN)~-J are mixed. (c) Calcium carbonate and mercuric fluoride are added to water. (d) Cadmium chromate is treated with aqueous hydriodic acid. (e) Boric oxide as added to aqueous KxMn04. (f) Aqueous Hg(Mn04). is treated with excess phosphorous &id. (g) The compound NOIFSOzis added to water
Familiarity with reaction chemistry also may arise from exercises in inorganic synthesis: (5) Devise methods for the following syntheses: (a) CuI from CuS ( b ) NaBH4 from borax ( c ) (NH&Cr207from Cr,O, (dl Na.S208 from FeSz (e) A1& from AI(NOa)3.9H90 (f) Anhydrous ZnI. from ZnS (g) Pb(NO& from PbSO,
Students should also have some appreciation of factors contributing to color in inorganic substances: (6) Predict which of the following would be visibly colored:
~m++ TiCI++
KO1
Si4
TTO++
Ph.0.
Some attention should be given to nomenclature: (7) Give unambiguous systematic names for the following: (a) Mn(CN)s (b) AgSO, ( e ) NH.CIOI (d) H.P*Os (e) (VOI)&OI (f) K&ln(CNh
Stereochemistry easily lends itself to exercises: (8) Sketch the possible stereoisomers of the following: (a) (NH,)(NOs)PtBrCI(b) Co(NH&CI, ( c ) Cr(en)dC*Od+ (4 Co(CNX(NHddNO4-
Students enjog working "compound A" problems, a type already extensively used in organic courses: (9) Identify the lettered species in the following seriea of reactions: Compound A is a. black solid; it is insoluble in water, dilute acetic acid, and sodium hydroxide solution, but dissolves readily in hot HCI, yielding a green solution, B. If solution B is boiled with copper wire, it becomes black, (solution C ) ; hut on continued heating the blaok oolor diseppems, yielding an almost colorles~solution, D. If D is diluted with a large volume of water, a white precipitate, E, forms. I3 dissolves in ammonia solution to give a colorless solution, F. F rapidly turns blue when exposed to air, (solution G). Addition of KCN to solution G discharges . the blue color. giving solution H. Treatment of H with zinc powder gives a. red-brown precipitate, I. insoluble in dilute acids and bases. hut soluble in warm nitric
A, is formed. (10) Identify the lettered compounds: Compound A is a white solid, dissolving in water to yield an acid solution. The neutralization equivalent of compound A is 75.4. A leaves a white residue on ignition. If A is treated with excess NaOH solution. solution B results. When a portion of solution B is treated with FeSO. and &SO,, it turns decidedly brown. A eecond portion of solution B is heated with NKC1 solution, yielding a white precipitate, D, nitrogen gas, and ammonia. Precipitate D is soluble in HCI but does not react with Has. A third portion of solution B is treated with acid permanganate solution. Upon boiling, there is liberated a red-brown vapor, soluble in CCL. This vapor, E, dissolves in dilut,e NaOH to give a colorless solution.
Of the two problems above, (9), for which compound
A is CuO, is quite simple, whereas (lo), for which compound A is NO+AIBr&-,is more difficult. Clearly, the variety of such exercises is limited only by the ingenuity of the instructor (and the time a t his disposal). Certainly an excellent course can be given without the use of any such exercises, but a course is generally enriched when the students are prodded into applying what they think they understand and when more is required of them than the assimilation of lecture and text material.
NORRIS AWARD TO BE MADE ANNUALLY THECommittee on the Norris Award, Northeastern Section, American Chemical Society, wishes to announce that by 1956 the Norris Award will be on an annual basis. The James Flack Norris Award shall be made for outstandine: achievement in the teachine of chemistry, particularly when demonstrated a t the college or secondary-school level rather than in the direction of research. Nominations for this Award should be sent to Professor Avery A. Ashdown, Massachusetts Inatitute of Technology, Cambridge 39, Massachusetts. There is no deadline. The Award is usually made in the late spring.
