SEMI-MICRO QUALITATIVE ANALYSIS for COLLEGE FRESHMEN J. LESTER DALTON Emmetsburg High School and Junior College, Ernrnetsb~r~. Iowa
0
NE of the most important advances in the field of analytical chemistry within recent yeassis the work in microchemistry. Most of this was necessarily research, and where i t was presented as in-
structional material, this presentation was to the advanced student of chemistry. It is interesting to note that microchemistry is growing fast and promises eventually to surpass macrochemistry in analytical deter-
minations. A. A. Benedetti-Pichler and J. R. Rachele (I) have a system for the analysis of the selenium group of Noyes and Bray. A. A. Benedetti-Pichler has published other microchemical methods of separation and identification of ions and has partially reviewed this in his article, "Qualitative Analysis of Microgram Samples" (2). Two papers which should increase the accuracy and speed of semi-micro or drop-reaction analysis are "Paper as a Medium for Analytical Reactions" by B. L. Clarke and H. W. Hermance (3) in which a more accurate delivery system is described for adding a given amount of reagent to a specific spot on the reaction paper, and "Applications of Confined Spot Tests in Analytical Chemistry" by Herman Yagoda (4). I n this latter article is described a method of controlling the amount of spread that a drop will make on a filter paper by waxing the surrounding area. Two other papers which have general interest in microchemistry and give an outline of the growing importance of this field are "Recent Advances in Applied Microchemistry" by Joseph B. Niederl ( 5 ) , and "General Microchemistry" by A. A. Benedetti-Pichler (6). All of these publications point to the growing interest and general analytical application of microchemistry. With the introduction and refinement of the semimicro or drop-reaction method of qualitative analysis, it appeared that it could be used in place of the more classical macro method for the last semester of freshman college chemistry laboratory. This change would be desirable from many standpoints. It would alleviate the clouded, smoke-iilled qualitative laboratory, and in this way make chemistry more useful as one of the general cultural sciences. This would achieve much toward placing chemistry on the popular basis which its present industrial and economic importance warrants. Another objection to qualitative laboratory work is the relatively large proportion of time which is spent on the purely mechanical processes of filtration, saturating with a gas, and washing of precipitates.? ,A benefit accorded the student and the administration IS the relatively lower breakage cost to the former, and the smaller quantities of reagents used in the semi-micro system. Perhaps the greatest benefit is the relatively more upto-date procedure which should make the student more valuable in the industrial or research laboratory (7). With these as goals, it seemed worth while to test the relative effectiveness, in the laboratory, of the semimicro and the macro method of qualitative analysis for the presentation of a course in chemistry to a class of college freshmen. With this study as the purpose, the class was divided so that there were about one-half of the students doing the laboratory work by the macro method and the other half were using the semi-micro procedure. I n this division of the class, care was taken to get an average group of students to cany out the work by the semi-micro method. To do this use was made of t h e student rating of their relative chemical aptitude as shown by the "Iowa Placement Examination" constructed by G. D. Stoddard, L. W. Miller, and Jacob Cornog ( 9 ) , and the ratings shown by the
relative class rank of the semester examination covering the first half of the course. This was an objective test of my own devising, but it was previously used and corrected to some extent for ambiguities. There were fourteen students who completed the full second semester's work. Only one dropped the subject during this period. He had no apparent interest in any of his subjects, and since he did no work in the chemistry laboratory after the first six weeks, no data are given in this study for him. The relative student rank which was used in selecting thestudents for the two sections is given in Table 1. TABLE 1 R A N K IN
APrrrona *No FIRST S B M s s r s a Ex~nnnrrroa A.rrogr
class rank 1 14
4 8 9
10 11
8 2 6 12 5
10
-
3
* scmi-micro method used by these students
Students numbers 43, 44, 45, 46, 47, 48, 49, and 50 were included in the group using the macro method of analysis. This included students a t both extremes of the class in relationship to their chemical aptitudes. The average of t k i r scores places this group in the fiftieth percentile. This would indicate that there is no undue weighting with exceptional or poor students. The average ranking of this group by the scores obtained in the semester examination was seven, which
was the median for the entire class. These data would indicate.that the students in the macro system of analysis were as near the normal in native ability and application as it was possible to obtain. (We shall refer to the students doing the qualitative analysis according to the macro method as section A.) Students numbers 51, 52, 53, 54, 55, and 56 were included in the group using the semi-micro method of analysis. (We shall refer to this group as section B.) These students were within the average in native ability as shown by their percentile rank. The rank in the first semester examination for this section was a little higher than the median for the entire class. The comparisons of these two groups are better shown by collecting the data into compact tabular form.
TABLE 3 TESTS USEDI N T B SBI~-MICRO ~ ANALYSIS
Gcrnol Ions
Conflmolory
9rcri9iran:
Remarks
:as1
Silver
HCI a d d
AgCl
Lead
HCI a d d H I add
PbCrO. PbCr01
Mcreurour mercury
HCl acid
Mercuric mereury
HzS acid
Aqua regia t o HgCh plus SnCh HgCIa
Bismuth
HIS acid
Metsllie muth
copper
Has a d d
cuxPe(CN)~
Cadmium
HIS a d d
CdS
Arsenic
HIS acid
Aotimony
HzS acid
Tin
Has a d d
Iron
NH.OH
Chromium
NH'OH
Separated from the eopper group by sodium polysulfide. Where there was an appreciable amount present t h e yellow sulfide was used ns t h e eonfirmator" test There war not complete satisfaction with this t e s t a. we used it. The separation from >he copper Soup i. described under amen," Reduction of t h e t i n wa4 carried out by reacting masncrivm dust with a dilute acid. Condderablc care needs to be exereired here Interfering anions are removed and the cation3 arc oxidired t o their higher valence. by boiling the s o l d o n with bromine The use of the perchromic a d d tert would be desirable here, but i t has not been ."ceessf"l Adsorption of the dye, aluminon,t o AI(0HJaprecipitate T p preeipitatea oxide and hydroxide aretreated with sodium bismuthate Nickel dimethyl- Thi. in probably one of t h e glyoxime most sensitive tests for nickel, and it. suaes. warrants the use 01 such a complex ion Cobalfie alpha- Ar for nickel nitroso-betanaphthol ZmFe(CNJa The confirmatory mmpovnd p'oduced i n the presence of oraoge IV gives a yellowirh green mioration BaCrO, and name tert srso, and name tert T h e oitrete is produced and CaCsO. and di.ro1ved in absolute acename test tone M~NH~POI K%NaColNO& Exes. ammonium ion must be removed Sodium zinc Phosphate*, and so forth, urany~ be removed, they i n t d e r e with the test Actionof vaprz Some of the water solution
Aluminum Manganese Nickel
Cobalt zinc
Barium Strontivm Caldum
Sodium
........ ........ ........
Ammonivm
........
Mngoesium Potassium
'
bir-
Dissolved by ammonium hydroxide and reprecipitated by adding nitric acid This covers the reactions for the lead which mmes down as the chloride and mlso ns the sulfide The mercurous mereury is oxidized t o the mercuric form by means of aqva red* and the resulting chloride reduced to t h s mercurous chloride and mercury by stannous chloride Bismuth hydroxide is reduced t o the black metallic bismuth by sodium rtanoite Te3ted io t h e presence of cadmium Copper is removed by treating with pota3sium wa-
: ................,t . .-
litmvr
+hp nri-n.~ .-.-.. samnlp is ..
made strowl? alkaline with sodium hydroxide and heated
All the scores given in Table 2 are averages of the group for which they are registered. This does not make them exactly authentic, and they are grouped in this way only for the purpose of comparison. These data show that the two sections are quite comparable in natural ability and application. The text chosen for section B was "Semi-micro Qualitative Analysis" by Engelder, Dunkelberger, and Schiller (8). This text was written with a view to use by more advanced students, and i t was necessary to limit the tests for the ions. For this reason one test for each ion was chosen from the list suggested and this test was used consistently by the students. For each ion that test was chosen whose reaction was within the range of the student's ability to represent by chemical equations. Occasionauy, however, it was n e c e s s q to use a more complex reagent such as the test for nickel, for which dimethylxlyoxime was used, and cobalt, for which alpha-nitrdso-beta-naphthol was used. A very brief consideration of the types of tests used are given in Tahle 3. This table will indicate that there have been no radical departures from the macrochemical reactions. The main changes are in the method of carrying out these reactions. No emphasis was placed on the anion analysis and the method described in the text for systematic identification was used The text used by section A was "Introduction to Qualitative Analysis" by Jacob Cornog and W. C. Vosburgh (11). There were no modifications used in the procedure, except that a test for the phosphate ion was added. The method of instruction used was to have the student run*preliminarytests in each of the five groups. All the ions for a given group were present, and the student was required to obtain good confirmatory tests before he was allowed to go on to the next group. In this way the student had first-hand experience and information on what to expect ii a routine experiment. After this preliminary work, each student was given two unknowns in solution. These solutions contained the ions in approximately 2 M concentration. Students of section B were given 1 ml. of sample for their analyses and those of section A were given 20 ml. This makes a range of from 0.05 gm. to Oil gm. for section B, and 1.0 gm. to 2.0 gm. for section A. The third unknown was analyzed for the anions only. The samples were of the same relative size as described above. Section A analyzed for the carbonate, nitrate, sulfate, silicate, chloride, and phosphate. Section B analyzed for cyanide, nitrite, sulfide, thiosulfate, sulfite, carbonate, arsenite, arsenate, phosphate, fluoride, sulfate, borate, oxalate, tartrates, chromates, ferrocyanides, ferricyanides, thiocyanates, iodides, bromides, chlorides, acetates, and nitrates. While section B was required to run the analysis for the list of anions given above, no emphasis Was placed upon any except the more common ones such as are listed under section A and those which mixht interfere with the cation analysis. ?he fourth unknown was a solid, which frequently required fusion before it could be brought into solution.
The size of the sample was about 0.25 gm. for the students of section B, and from 5 to 10 gm. for those of section A. This was analyzed for both the cations and the anions. The fifth experiment was the preparation of a commercial product. The formulas used were those in "Chemical Formulary," Volume 111, edited by H. Bennett (10). The sixth experiment was an analysis of a comparable commercial product, in which the details for the identification of such organic compounds as were present were given to the individual student as he required them. These directions were gathered from various sources of which "Standard Methods of Chemical Analysis" by W. W. Scott (12) and "A Systematic Identification of Organic Compounds" by R. L. Shriner and R. C. Fuson (13) were the most useful references a t hand. The results in the two groups which were obtained by this method of instruction are given in a compact form in Tables 4 and 5. TABLE 4
R ~ r r n r aOBTAINBDm QUALI~ATWE A~*&usrsex S B C ~ D EN Sludanl number 61 52 53 54 55 56 Avunge
Lobordory hovrs YO 95 100 105 100 94 97
Colionr rcporlcd 22 22 25 21 32 28 25
Anions rcporlrd
T o l d ions
19 7
17 4 17 13 13
Orcsenl
Pcrcrnloge of ionrfound
51 54 65 33 62 58 62
SO 54 76 76 70 71 73
.
TABLE 5
Rstrazs OBTA~NBD EN QUALTTATIVB ANALYSES BY SBETIOW A Sludrnl nwnibrr 43 449 45 46 47 48 49 50
Average
Lnboralory hours 106 100 103 100 118 100 108 108 105
Calions rr9orled 24 5 20 16 28 31 12 5 18
Anions rrporlrd
Tololions Pcrranlon prcrcnl ofiorsfo~nd 35 80
4
.5.
..
38 29 41 40 29 26 34
3 3 4 4 4 ,4
* Much undirected work due to lack of ability.
..
66 66 76 88 55 35 67
then became difficult to keep the students in section A from feeling somewhat abused. In fact, all the students in the laboratory were very much "sold" on the semimicro method. It is also an important consideration in the smaller colleges and high schools that the unpleasant odors of the chemistry laboratory be kept a t a minimum. In the macro method of analysis this was a major problem, as it was frequently necessary for the student to boil off hydrogen sulfide and sublime some ammonium chloride by baking. Four or five students carrying out these operations simultaneously overloads the normal ventilating system and clouds the laboratory and much of the school building within a very short time. In the semi-micro method the amount of these gases or fine particled solids were so slight that they could be readily removed. The economical administration of a chemistry course is also one of major importance to the small college and high school. Considering the breakage cost per student per semester, the average for section B students was approximately sixty cents; for section A one dollar and twenty-five cents. Administration costs for section A were approximately three dollars and fifty cents per student per semester, compared to two dollars for section B. There remains the consideration of the comparative general instructional value of the two methods used for the laboratory work. The best comparison which we have is the relative rank of the students in their aptitude tests and in their semester examinations. These comparisons are given in Tables.6 a i d 7. TABLE 6
on TBB RANKS IN TBB C L AO ~ XS ~ B ~ OR N STODBNTSIN T e s l l APTTTMB.AND FIRST A N D SBCOND SBYBaTBB EXAYINATIONS
:OYP-PON
Sludrnl
nu"&. E
From these data i t is worth noting that the students in section B did one and one-half times as much work in the laboratory within a shorter time and with more satisfactory results than the students in section A. Since these two sections differed only slightly in their native ability and application as shown in Tables 1 and 2, these results must be attributable to the greater effectiveness of the semi-micro method of analysis. An important consideration in a study of this type was the student reaction to the differentworking conditions. There were few, if any, of the section B students who entered the laboratory for the second semester's work with any marked degree of enthusiasm.' In fact they rather resented the part of "guinea pigs" which they considered they were playing. It required about three weeks of laboratory work to convince them that they really had the better end of the bargain. It Many of the errors and steps needing special attention are given by G . W. SMITH in his article, "Teaching of qualitative EDUC..15, 324 analysis by the semi-micro method," J. CHEM. (1938).
51 52 53 54 55 56
Average
APIiludc Dcrcmlilr
rank 70 50 50 60 20 70 53
P*9 Scrond srmerlrr remcrlrr c x ~ m i n o l i m ' ~rominolion rank rank
.
2 4 12 6 8 3 5
2 Y 12 7 3 6 6
Quoliloliac onnlyris rank 2 la 5 7 4 8 7
TABLE 7
C O ~ P A F S S OOF N ~TAB RANKSIN TUB CLASS 01 S B E T A ~ STUDBNTS N r~ T.sm A N D PIRJI A N D SBCOND SBMBSTBE EXIMINATIORB APTITUDB,
Sludrnl nvnhc*
Apliludc pnrcnlilc
rank
Fir91 rcmcnrr rromindion rani
S~cond scmcslrr rroniinolion
rank
Quolilnhvr onnlysis rank
These results show that the students in section B have retained the small advantage which they possessed over section A and have been able to add a little more to this advantage. These results are not so much
different that they would warrant the claim that the use of the semi-miao method used in the laboratory increases the instructional value of a course to freshman college chemistry students. They do warrant the statement that the use of the semi-micro method is as effective in the freshman chemistry course as was the macro method of analysis. For these reasons it is obvious that the introduction of the semi-micro method of qualitative analysis into the college freshman chemistry laboratory tends to (a) make the general chemistry laboratory a more congenial place for the student to work, (b) eliminate much of the time-consuming, purely mechanical processes, (6)
save the student in general breakage costs and the administration in general supply costs, and ( d ) introduce the student to the more modern and usable methods of industrial and research laboratories. These are the benefits to be derived from the adoption of the semimicro qualitative analysis for the second semester's work for the college freshman chemistry course which includes a semester of qualitative chemical reactions in the laboratory. There are no apparent drawbacks to the use of this method. The author wishes to acknowledge the splendid cooperation which he received from Dr. J. A. Greenlee, Dean of the College, and Superintendent R. W. Newell.
LITERATURE CITED
I RBNEDETTI-PIC~ER AND RACHELE. Ind. Ene. C h m . . Anal. Ed., 9, 589 (1937). ibid., 9, 483 (1937). (2) BENEDE~I-PICRLER, AND HERMANCE. ibid.. 9, 292 (1937). (3) CLARKE (4) YAGODA, ibid., 9, 79 (1937). (5) NIEDERL,ibid., 7, 214 (1935). (6) BENEDETTI-PICALER, ibid., 7, 207 (1935). J. CHEM.EDUC..14, 561 (1937). (7) CLARKE, (8) ENGELDER, D-ELBERGER, AND SCHILLER,"Semi-micro aualitative analvsis."' Tohn Wilev & Sons. Inc.. New . . e o r k City, 1935: (>-,I
(9) . . STODDARD.MILLER. AND CORNOG,‘Tows Placement Examination" (New Series C. A. Form Y). State University of Iowa Press Publication, Iowa City, Iowa. 1930. (10) BENNETT,"Chemical formulary," D. Van Nostrand Ca.. Inc., New York City, 1936, Val. 111. (11) CORNOG AND VOSBURGH, "Introductory qualitative analysis," The Macmillan Co., New York City, 1928. (12) Scorr. "Standard methods of chemical analysis," D. Van Nostrand Co., Inc.. New York City, 1925. (13) SHRINERAND FUSON,"The systematic identification of organic compounds (authors' manuscript)." Edwards Brothers, Inc., Ann Arbor. Mich.
