STIMULATING QUESTIONS IN QUALITATIVE ANALYSIS EARL J. SERFASS, RALPH F. MURACA, and RALPH G. STEINHARDT, JR. Lehigh University, Bethlehem, Pennsylvania
Tm
Question 9
Question I
An itinerant opium peddler is suspected of murdering an apprentice in a machine shop. The filings which adhered to the peddler's shoes are submitted to you for analysis. Your results are as follows: The filings are oompletely soluble in apua regia. The solution is neutralized and NH40Hand NHGI are added. Upon saturation with HzS the mixture is separated into Solid I and Liquid I. Liquid I is treated with (NH&S04 and (NH4)2Cp04. No precipitate is obtained. Upon treatment of a portion of Liquid I with KOH, the odor of NHz is noticed. The addition of NaNHr HPO, to Liquid I gives a faint white precipitate. Solid I is treated with 1.2 N HCI for one minute and dissolves completely. The solution is boiled, neutralized with NazCOs and treated with NarOa. A reddish-brown precipitate is formed which dissolves in HCI and gives red color with KCNS. The reddish-brown precipitate is designated as Solid 11. Liquid I1 which was separated from Solid I1 is yellow. It is boiled, treated with HCI and NH.CI, and, upon addition of NH'OH, an almost transparent, jelly-like precipitate is noted. The supernatant from this precipitation is treated with acetic acid, NH4Ac, and BsCI2. A yellow precipitate is formed. The remaining supernatant liquid gives a precipitate witb K4Fe(CN)~. The machine shop in which the murder occurred has, during the past week, been working on the alloys the compositions of which are designated in the. following table:
necessity for subjective examination questions has recently been admirably emphasized by J. H. Hildebrand.' For several years, qualitative analysis quizzes and examinations a t Lehigh University have been characterized by "paper unknowns" in which the student is presented with the data obtained in the analysis of an unknown and is asked to give correctly the ionic composition of the sample. The data usually is presented without regard to laboratory procedure and the student who merely memorizes the qualitative analysis scheme almost invariably receives a lower grade than the student who studies the inorganic chemistry of the elements with which the scheme is concerned. Recently, the "paper unknowns" took on a new and more interesting appearance. The questions which appeared on the quizzes of three sections are given below. It is recognized that further reading in archaeology and metallurgy might improve the validity of the data given. The quizzes covered only Groups 111, IV, and V. In order to ascertain the make of the vehicle which was involved in a. hit-run accident. the anlv bit of evidence. a. small plcce of radiator grille, W : L ~s h ~ " t t r dto ywr for annlyai+. You ohtainrd tlrr followiuy experimeutrl il;rt.,: The snmple w s hssolrcd rn 6 .V 1iCI by prolonged heuing. Only a few minor specks of material remained; these were ignored. The solution of the sample was made ammoniacal and wturated with HB, whereupon Solid I was deposited. Solid I was separated fram the mother liquor (Liquid I). Solid I gave B green borax head and a black sodium carbonate bead. Solid I was dissolved in 6 N HNOs; neutralized with 6 N KOH and treated with Na>O,; the resulting Solid I1 was separated fram yellow Liquid 11. Solid I1 was dissolved in 6 N HNOs giving rise to Liquid 111. Liquid 111gave a red color with KCNS. Liquid 111, when made stmngly ammoniacal precipitated a small quantity of a brown, gelatinous precipitste. The supernatant solution was blue and turned dimethylglyoxime naner red. Liauid I1 was carefullv neutralized with 6 N HCI and then made atrongly ammmisrxl; no preerpltatc formed. On the b3sk of the folloa,mg daru of the composition of rlre radiator grillrz of sevrrnl suwk wrs, which car waa rnvolvcd in rlte accident and give the reasons for your choice.
..
Cr
Ni Cu Mn A1
Zn
X
X
Chevrolet Ford Pontiac
x x
x x
PacLasd Plymouth
x x
x
x
x
x
X
X
.
x x
Co
Mg
.
x
. . . . . . . . . . .. x . . . . x
x
.
X
. . . .
..
x
Fe X
x
x
.
x
x
HIWEBF~ND, J. H., J. CHEM.EDUC., 26,450 (1949).
. . . .
x
x
..
Fe Cu Co Ni Zn A1 Cr
Low-cmbon steel x Spec. Steel No.
5
X
Mg C Si
..............
x
V
....
. . . . . . . . . . . . . . . . X X X . . . . . . . . . . . . . . .... x . . x ...... .. x.. . . . . . . . . . . . . . . x .. x . . . .
Spec. Steel No. X . . X 9 Dural ...... Soft brass . . x . . Chromesteel x . . . .
Is there any definite evidence that the peddler murdered the apprentice? Give a complete report on your findings.
Question 3 The ante-chamber of the Queen's suite in the tomb of TutAnkh-Amen is decorated witb predominantly red figures. A small sample of the red matter was scraped off the wall and submitted to you for analysis. Preliminary experiments showed that no organic substances were present and that the material would dissolve on prolonged heating with HCI leaving an inert, white mass of silica. The HCl solution was rendered rtmmoniacal, saturated with HS, and the sulfides (Solid I ) were separated from the supernatant solution (Liquid I). Sohd I gave a light green borax bead and a green sodium carbonate bead. &lid I dissolved completely in 3 N HNOt giving Liquid 11. A drop of Liquid I1 gave a blood red color with KCNS. When Llquid I1 was made ammoniscd a gelatinous brown solid precipitated (Solid 11) and the supernatant liquid colored dimethylglyoxime paper red.
AUGUST. 1950
463
Liquid I gave a voluminous, white solid on treatment with (NH4)&Ob and a clear, colorless supernatant, Liquid 111. Spectroscooic examination of Liauid 111 showed a red and a blue line a i the ends of the visible spectrum, together with a yellow line. Liquid 111 gave a brilliant, yellow %me test. A mnrey some ,f the ,,,inerala in the rvea of the pramids is given below: On the basis of your analysis m d assuming that only the above
Mineral Limestone Goethite Orthoclase Chromite Glaucophane Psilomelane Willemite
Fe
Al
Mn
Ni
x x
..
x
..
..
x
x
.. x
.. .. ..
x
.. .. ..
.
x x
x
.. .. .
.
Co ..
.. ..
.
.. x
x
..
..
.
The results indicated that the students were able to answer the problems with unusual intelligence; and the composition of such problems is more enjoyable to the instmct~rsneed not be emphasized.
CI .. .. ..
..
.
minerals were used in making the paint, list the minerals present or absent. Give the reason for listing a mineral as absent.
x x
.. .. .
.
Ca
Zn
.. .. .. .. ..
x
.. .. .. .. ..
..
x
.
.
Ba
Sr
..
.. .. .. .. .. .. ..
..
..
.. .. x
..
Ma
Na
K
x
.. ..
.. ..
.. .. .. .. ..
..
.. x
.. .. ..
x
..
.. x
..
Si '
x
x x x x x x
