A Comparison of the Semimicro A d Macro Methods the Teaching of Elementary ~ualitativeAnalysis KFANETH L. WATERS1 University of Georgia, Athens, Georgia INCE Engelder and Schiller (1) described their success using the small-scale technique in the teaching of elementary qualitative analysis, there has been rather wide acceptance of the semimicro method of laboratory instruction. Some excellent endorsements of the newer technique have appeared in THIS JOURNAL. Degering (3) gives a sevenfold count of advantages of the semimicro procedure over the macro procedure. He stresses the point that the semimkro technique will give the student an invaluable training in armrarv be of inestimable value regardless ~-. -. . -.-. ,that will --of the vocation which the student mav choose. Dalton (Z), in a detailed study of results of selected students using both schemes, reached the conclusion that the semimicro technique Was as effective in instnlction as the macro technique. Smith (4) has shown that the results of student analyses compare favorably by both procedures. Some writers (5, 7). have stressed economy as well as other advantages of the semimicro procedure. Regardless of these recommendations, some teachers are still dubious of the semimicro procedure, fearing that accuracy has been sacrificed for speed and convenience. I t was thought that i t would be interesting to make a comparison of classes of students using the two techniques. Dalton (Z), in his comparison of the two techniques, used a few selected students and Smith (4)used different texts. It was the purpose of this comparison to find out in an unbiased manner just what analytical results would be obtained by "run-of-the-mill" students using two procedures which were as nearly identical as practicable. The essential difference was a reduction in volume of reagents employed and the substitution of a centrifuge for filtration. Classes used for the comparison were regularly enrolled students who had completed two quarters of general &em~stry. Students were not subdivided according to previous grades or aptitude tests. The macro pro@ure used was that of Scott (8) whlch had been used in the department for a number of years. The semimicro ~rocedurewas adapted from the macro procedure and made to conform as nearly as practicable to it. The procedure was given a preliminary trial by an experimental class before being used by the classes reported in the comparison. First reports of all students were counted. Second reports or repeats were not counted in the tabulation. Unknowns were counted as correct
S
-
~~
1
~~
-
if all ions present were reported and no additional ions were reported. In the summary of students' reports on the cations, the per cent correct report is based on the number of times detected when present. The number of times reported when not present is tabulated separately. Tables 1 and 2 give a summary of the reports of all students who started the classes. TABLE 1 SUMHAXY 0s STUDENT RRPORTSON
T o l d Number Unknorunr
???'micro l".acr"
3
,..
UNKNOWNS
Par Cent RePorlod CDIIICUY
,""
~t is not claimed that the results of the classes reported in these tables are typical of the results which would be obtained with any scheme of analysis. When compared with the class results reported by Smith (4), in his comparison of semimicro and macro procedures, and with the results of Gilbertson (6),who has made an extensive study of student results in macro qualitative analysis, it appears that schemes of analysis vary in the ease with which the dierent ions are detected. Although Smith (4) and Gilbertson (6)have indicated that i t is not uncommon for students to report positive tests for ions when absent, i t is thought that the number of excess ions reported by the students of these classes is unusually large. This zealousness of the students to report ions not actually present may be due in part to the policy of refusing to assist the students to make up their minds in doubtful cases. It was noted in most repeats that the students withdrew the questionable ions in their second report. In the macro procedure there was a greater tendency for the students to become confused on a test and make a positive report. Critical examination of the tabulation will lead one to assume that the schemes of analysis are at fault in the case of some of the ions reportedincorrectly. This is undoubtedly a correct assumption; however, it is not the purpose of this paper to point scheme, but to comout the merits of any pare the semimicro and the macro techniques. It might be mentioned a t this point that such a tabulation has brought out certain "bad spots" in the schemes which were in need of correction. Some of these have been modified to give better results. CONCLUSIONS
Present address: Mellon Institute. ~ i t t s b n r ~ ~h e, n n s ~ ~ v a n i a The results of the unknowns indicate that students 493
Na NH. M g K
41
4.5 41 50
Total 993
89 80 84 87 80
2 7 5 10 8
66 57 58 40 50
91 90 91 88 90
100 88 98 81 89
5 2 19 3 9
71
97 96 96 95
76 66 85 85 95 88 87 98 88
4 4
3 0 3 7 0 13 20
-
Av. 89.2
Total 136
obtain more accurate results using semimicro technique than when using the macro technique. It is believed that a tabulation of student results such as Table 2 is of value, not only in indicating the weak spots of a scheme of analysis, but in the actual evaluation of student unknowns.
53 55 56 64
91 68 94 92 95 97 96 98 97
-
0 I 0 5 4 3 1
13 17
Av.
98.4
Total 121
a t whose suggestion this comparison was made. LITERATURE CITED
(1) ENGELDER AND
SCHILLER; J. CHEM.EDUC..9,
~2~~;~$;df'i6f8&~1("f~~i)~
(4) SMITH. ibid.. 15. 324 11938).
(5) D ~ B B I N S AND ~b ACKNOWLEDGMENT
1
0 9 2 8
88
54 56 66 62 58 69 48 60 69
Total 1462
3 10 11 6 13
(6) GILBERTSON, ibid
1636 (1933)
