JOURNAL OF CHEMICAL EDUCATION
STUDENT RESULTS IN QUANTITATIVE ANALYSIS R. D. COOL University of Oklahoma, Norman, Oklahoma
D m ~ cRECENT years insistence on perfection of technique and high precision and accuracy in beginning courses in quantitative analysis for mixed groups of students has been decreasing. In order to collect information about the laboratory results which can be readily obtained by average first semester sophomores, records2 were collected over several years from classes incIudimg chemistry, chemical engineering, pharmacy, premedical, and applied biology students who were furnished with fairly good equipment hut wcro inado 1
Present address: M ~ d i s o nCalleee. Hnrri,wnburu Vireinia.
J. R., "Manpower f o r ~ e s e a r c h , "U. %. ~ & r n ment Pr~ntingOffice, Washington, 1947, Vol. I V of "Science and 2 STEELMAN,
Public Policy," p. 154.
quately housed-which seems to be the usual condition. Each student was issued just enough sample to run a determination in doplicate. If repetition of the work was required enough of a diierent sample was issued for a new determination in duplicate. This prevented the procedure, sometimes resorted to, of running a number of determinations until two out of the total number check within some prescribed difference. It also promoted careful and neat working habits and kept the sludent from developing the opinion that an analysis must bc accurate just because results obtained by the same procedure check closely. In order to have the figures in the table represent
FEBRUARY, 1949
101 Table 1 Student Results in Quantitative ~x&sis
Sample Potassium acid phthalate Sods. ash Dried blood
Soluble chloride
Method
Alkalimetric Acidimetric Kjeldahl lMohr
(%Ed Ferrous ammonium KMnO. (reduction with & n i n u m ) sulfate KMnO. (reduction Iron ore with aluminum) KnCnOl (reduction Iron ore with SnCW Iron are Ce(S0,)s (reduction with SnCL) Park Copper ore Dimethylglyoxime Nickel ore BsSO, Soluble sulfate Cupric sulfate solu- Electrolytic
Average Average Average deviation difference rleviatim of a single of arithmetic between mean from duplicate resnlt from manufacturers determinatias, Number Number arithmetic mean, in parts valtz, in parts in parts per of of per thousand thousand students samples per t h s a n d
Average value of samples
20 18 20
.. ..
21
10 21 23 21 20 12 31 18
tion
30 9 Mg2PsOl 26 9 Iodometric 38 8 Iodometric A1208 39 9 KMnO, (after excess 30 8 Na,C,O,) Precipitated nxalate, 27 9 Calcium carbonate weighed carbonate Sodium hydroxide Standardization with hydrochloric acid solution Potassium thiocva- Standardization with silver nitrate grtnate Potmsium perman- Standardization with arsenious oxide ganate Standardization with iron wire Ceric sulfate Standardization with electrolytic copper Sodium thihsulfrtte Iodine solution Strtndardization with arsenious oxide
Magnesium sulfate Tartar emetic Stibnite Alum P,vrolusite
.. ..
*21 +22 + 7 +24 113
f34 *9 *8 +26 + 12
5
18.97% MgO 19.15% Sb 23.25% Sb 5.95% Ah08 70.34% JInOr
*
+
9
4
28.97% CaO
9
4
7
i 2 4
6 4
4
averages for all students, both satisfactory and unsatis- Records for magnesium sulfate and tartar emetic infactory reports have been included in the computations. cluded only the final average reportedby each student However, in order to exclude "huge" errors which and data were not available for determining the differmight lead to unwarranted conclusions, results with ences between duplicates. Procedures followed in most cases were those of deviations from their respective arithmetic means greater than four times the average deviation of a single Willard and Furman? Procedures by Rieman, Neuss, result8 were not included. This seems to be the most and Naiman6 were used for the nickel ore, stibnite, and frequently used criterion for rejection of widely diver- alum. Copper was deposited electrolytically on a copper gent values and the number of determinations on each gauze cathode by a procedure developed locally by sample was small enough that use of the less familiar Prof. A. C. Shead. Most of the samples came from firms which prepare Pierce-Chauvenet criterion4did not seem justified. Except for the average difference between duplicate and distribute this type of material. A few were predeterminations, results for the Mohr, Fajans, and pared locally. Reagent grade chemicals used by the Volhard methods for chloride have been combined be- students for volumetric primary standards were checked cause aliquot portions of the same sample were used for against standard samples issued by the National each. Different samules of iron ore were used in the Bureau of Standards. pmnangsnate, dichromate, and ccric sulfate merhods. CODDWIS. 11. M.. '.Prerision of hIeasurerncn~sand Grunhirnl Methods," ~ c ~ r a v . - ~ iBook l l Company, New York, -1920, p. 21; CRW~~PLER, T. B., AND J. H. YOE. "Chemical Compuhtions and Errors," John Wiley And Sons, Nbw York, 1940, p. 185. ' CRUMPLER, T. B., AND J. H. YOE,ibid., pp. 180-190. 3
WILLARD, I(. If., AN!) S . H. FIIRIIAS.'.Elementary Quanritnti\.c Analvsii." Kcw Yo&, . . 3nI ed.. D. Van Knstrsnd Company, ~~
1940. 0 RIEMAN, W., J. D. Nsuss, am B. NAIMAN, "Quantitative Analysis," 2nd ed., McGraw-Hill Book Company, New York,
1942.
