JOURNAL OF CHEMICAL EDUCATION
THE RARE ELEMENTS IN FRESHMAN CHEMISTRY SIGFRED PETERSON University of Louisville, Louisville, Kentucky
.. T m s i s n o a t t e m p t by the author to advocate burdening freshman chemistry students with the chemistry of the rare elements. The average student is sufficiently burdened in learning the chemistry of a few common elements along with developi6g an understanding of the elementary principles of chemistry+ It is the purpose of this paper to suggest means of taking advantage of the student's ignorance of the chemistry of the rare elements in testing his understanding of chemical principles. Let us suppose that the student is given the problem: "0.327 g. of zinc is dissolved in an excess of dilute sulfuric acid to give 112 ml. of dry hydrogen a t STP. What is the charge on the zinc ion?" Obviously the student who has duly memorized his "valences" will find some combiatiou of numbers which will give the answer "2." But if the problem involves gadolinium, hafnium, or thallium the student will be forced into solving the problem, and the instructor is spared the need for inventing hypothetical elements. Some uninformed freshmen believe that balancing of oxidation-reduction equations is such a difficult labor that i t is desirable before quizzes to memorize every equation in the textbook. But if the examination ques-
tion calls for an equation for the oxidation of Np+' to NpOz++ by Br0,- the student must learn the easy method. Sufficient chemistry of the transuranium elements has been published1. I that the instructor can devise plausible examples. Vanadium, rhenium, tellurium, and other uncommon elements also have interesting sets of oxidation states which can furnish a wide variety of equations to balanre, electrochemical equivalent problems, and other exercises based upon changes in oxidation number. To illustrate the principle that properties of dilute salt solutions are actually properties of the ions, the following examination questions have been successfully used. Both unfamiliar properties and unfamiliar elements are illustrated. No great modifications are needed to adapt these questions to the machine-graded multiple-choice type. "In the following list of salts, the colors of dilute solutions are indicated by c for colorless, y for yellow, p for pink, g for green. Fill in the color of those not given. ~HARVEY B., G., H. G . HEAL,A. G . MADDOCR, AND E. L. Chem, Sot,, lolo (1947), r~,,,,,,, M ~ ~ AND~ L ~~c B ~~ ~ ~~J .L dm. L~ ~ ckm. ,N , SOC., 71,687 (1949). ROWLET J ,
JULY, 1949 AgNOa Ca(V0h TmCh Eu(NOJr
379 c Y p
AgCl01 LU(NO~)~ Lu(VO& Tm(ClO&
g
::$1"0&
Dy(VO& LuClr
Y c
c
"By measurements with a Gouy balance it is found that solutions of CuSOn, Nd(NO&, and KeMnOr are magnetic while solutions of K2S04, Ba(NO&, and LaCI, are not magnetic. In the following list of salts, underline those whose solutions are magnetic, cross out
those which are not magnetic, leave unmarked those you can't tell." KNOJ
CuCb
Lan(MnO&
NddSOda
Laz(SOi)s
It can be added that the use.of examination questions of the type suggested here will give the student, perhaps not painlessly, a consciousness of large regions of the periodic table otherwise unexplored in the freshman course.
