PACIFIC SOUTHWEST ASSOCIATION O F CHEMISTRY TEACHERS
THE USE OF "PARALLEL SAMPLESff I N QUALITATIVE 'ANALYSIS COURSES' GEORGE B. KAUFFMAN Fresno State College, Fresno, California
ATTHE
130th American Chemical Society meeting in Atlantic City, the Division of Chemical Education held a symposium on "Qualitative Analysis-What, Why, HOW?"^ The symposium recognized that t,he trend in college curricula today is to eliminate qualitative analysis as a separate course and combine it with the course in general chemistry. I t is not the purpose of this note to debate the merits of this current approach, but rather to recognize the lessened time available as a fact and t o suggest one procedure to ameliorate the situation. As an alternative to analyzing separately the known and then the unknown, as is done in some schools, the author suggests that the student analyze the known and unknown simultaneously, "in parallel." This procedure is particularly convenient in semimicro courses where centrifugal separation is used instead of filtration. Instead of counterbalancing the tube containing his known solution with a tube of water, the student uses a test tube containing his unknown. The most obvious advantage of this proposed method is the saving in time, a precious commodity in today's "qual" course. This saving in time may help prevent undue pressure and restore the fun that should he part of a good course. Secondly, the new procedure vividly introduces the student to the important concept of the control. The author has observed that some students fail t o see the link between the known and the unknown, especially when a period of time has elapsed between the two, as is often the case under the alternative system. The student wisually compares his unknown with his known rather than mentally comparing it with a written description in his notebook. Often, in order to discourage "dry lahbing," we tell students that many color reactions, precipitates, etc., cannot he adequately described in words, but must actually be seen. What better way is there to drive this point home than to have the student actually make the comparison? A third advantage of the new method is its effectiveness in reinforcing the value of the pnknown as the student's first and best opportunity to utilize the scientific method and to build confidence in his own Presented before the Division of Chemical Education s t the 133rd Meeting of the American Chemical Society, San Francisco, April, 1958. 130th Meeting, American Chemical Society, Atlantic City, 34, 387-402 (1957). September, 1956; J. CHEM.EDUC.,
VOLUME 35, NO. 7, JULY, 1958
practical scientific ability. Often instructors are plagued by students who rush up to them waving a test tube and ask, "Do I have sodium in my unknown?" If the student were holding a test tube containing a known in his other hand, his question would he answered in many cases. Most students will eagerly meet the challenge of unknowns as a test of their ability, aud they are often happier if they can be on their oxvn and not depend on the instructor for decisions. Thus, the anti-authoritarian nature of science is practiced as well as preached. As a logical extension of the "parallel sample" idea that requires only a slightly greater expenditure of time, some students may wish to analyze a third sample, a blank. Comparing.his unknown with his known and blank will usually help the student make up his mind and also demonstrate to him that what he is seeking is not merely a result which occurs when the ion in question is present, but that this result must be d
