Laboratory Work in QuantitativeAnalysis for Nonmajors George F. Atkinson and 1.Rudemky University of Waterloo, Waterloo. Ontario, Canada N2L 3G1
For a number of years we have operated a quantitative analysis course with lab for nonmajor students. These range from very bright persons aiming for medical school or business school who desire a short, broad view of science to persons required to withdraw from major programs. We decided the interconnectedness of analyses, the need
Key:
for crosschecking results for self-consistency, and the need for chemists to work cooperatively, assessing and trusting each others' results, should he main thrusts of the lab work. Accordingly, students were paired arbitrarily and presented with the menu of experiments shown in the table and interrelated in the figure. In this scheme, each student per-
Numbers on lines are e x p e r i m numben in me ounine. Boxes haw We meanings shown below
a given as
0 given as unstd. sol".
Interrelationship of experiments.
Us1of Experiments and Working Scheme NO.
Titie/description
1 2
Skills tests (done pn check-in day) Detn. Agt by precipitation with either CI- or B T (Each pannenhip submits one final reported value.) Stdn. HCI against sadium carbonate pri.std. Stdn. NaOH against potassium hydragen phthalate pristd. Crosscheck standardized HCI and NaOH Crosscheck standardized HCI and Ag+ Stdn. oxalic acid against NaOH Stdn. KMn04(soh, supplied) against oxalic acid Detn. Fe in a salt using KMn04 Detn. Ca2+ with std. EDTA supplied Detn. Cazt by oxalate-permanganate method
3 4 5 6 7 8
9 10 11
Repon required
Refwen~e' handout
x
To be done by panner A B X
X
use Ci-
use Br-
X
X X
x x
X X
X
x x x
X
X
X
X X
X
a paw numbers refer to skwg & west, "~undamentalsof ~nalytical c h e m i r ~ . " 3rd ed.. How.~inshart & winston. N differences in form of sample (solutionversus mild. acl.
~ W YO*.
1970. ~ ~ c e d u r described aa are in eome cases modifled by
Volume 63
Number 1
January 1986
83
formed seven experiments in triplicate during the 11threehour working periods in a term. This allowed time to repeat any experiment in which submission of an unknown report had led to a failing mark. In view of the varied backgrounds and performance levels of the class, the lecture course began with explicit treatment of each experiment and its related calculations before moving to more general topics and treatments. T o address the same problem, we begin the lahcourse with a skills test which is a simple subset of Harris and Kratochvil's tests.' The student reports the masses of a set of numbered tares, and the volume readings of a set of sealed-off portions of broken burets partially filled with water. Then, a portion of standardized hydrochloric acid is pipetted and made up in a volumetric flask, from which an aliquot is
84
Journal of Chemical Education
pipetted and titrated with standardized sodium hydroxide. These exercises enable lack of basic skills to he identified quickly so appropriate help can he given. This course has been successful in instilling technique and concern for precision relevant t o other courses the students mav take. Reasonable success resultine from honest effort produces a positive attitude in the c G s s . ~ ~ suggest e the ~ r a c t i c ehere exem~lifiedof chaining a numher of exoeriLents together is useful because of tce sustained chalienge to keep errors under control which it presents. ~
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Harris. W. E.. and Kratochvil, B., "Chemical Analysis," Barnes 8 Noble, New York, 1969, Ch. 1.
