Programmed Independent Study, Laboratory Technique Course for General Chemistry
Olaf Runquist Hamiine University
St.
Paul, MN
In an effort to increase student learning efficiency and decrease faculty teaching load we designed a programmed independent study General Chemistry Laboratory course. We have now completed the second year of experience with the course and have found that i t has been very effective in achieving the two principal objectives(1)
to reduce faculty laboratory teaching load by at least 50%(from 16 to 8 hrlwk).
The lahoratory course has been used with students enrolled in hoth regular and accelerated General Chemistry courses (total of about 100per year). The emphasis was strictly to develop good technical skills with no attempt made to relate the laboratory experiments and classroom topics. I n order to finish the laboratorv with an "A" mark, students had to complete with acceptable precision and accuracy (1%or better) eight quantitative lahoratory "projects" and hoth a written and practical examination. Students were allowed to work in the lahoratory any time the stockroom was open and a t least one faculty member was readilv available. All experiments were low risk and during the two year period we had no accidents. Faculty were available for consultation in the lahoratory 1.5 hours each of four afternoons (very little productive use was made of faculty during these periods and our future plan is to have a faculty member "on call" in his or her office during these times). When students wished to work in the lahoratory, they would check out an experiment kit from the stockroom. Each kit contained a tape recorder, an instruction tape, visuals (for some experiments taped-slide lectures were used) chemicals, and glassware. The tape and visual materials gave detailed instructions on the techniaue and practice exercise routines. After the student had completed the tape and practiced the technique, a project would he completed which required a
precise execution of the technique. For example, the project relatine to the use of oioets . . and volumetric flasks.. reauired . studenrz to pipet a 10.67 1111" sample [use of two typrs of piprrsi ~f R .krocV iolution infoa 50 r m ' volumetric flask, dilute t o the mark, mix and suhntit a '2.5 ml aliquot tor gmding rtr~rdic:~te samples re~uired,.'l'hesesamplt.s w i w graded by student assistants, and if the results were within the acceptable precision and accuracy range, credit was given. Unacceptable projects could he redone for full credit; students were strongly encouraged to have a faculty member observe their technique if they were repeating for a third time. A public "scoreboard" was used to keep students abreast of their pnBgrris. Most grildioa i r a s completed within 21 hr and unalwcrssful reports vere returnecl with some indication d t h e o r error and nossihle causes. Table I lists the exauienitude " periments, a brief description of the project, and the grading method. At the end of term, a final examination was scheduled. One week urior to the exam. students were ~ r o v i d e dwith the information shown in theAppendix. All four written examinations were different (hut equivalent) and molarities given in stock solutions were changed each test day. ~ a b b r a t o r y proctors were provided (hut not really needed). The practical exam was graded on the basis of 60 points (0-1% error, 60 points; 1-2% error, 50 points; 2-3s error, 40 points; etc.) while the written exam contained 40 points. Table 2 summarizes our experience during the past year. Students were asked formally to respond to the lahoratory, both by an anonvmous auestionnaire and hv a class meeting with the ~ e ~ a i t m echairman. nt The respbnses were overwhelmingly favorable. Criticisms tended to relate to quality of sound production on tapes and tardiness in grading. We were surprised a t the lack of criticism of the rigor or "irrelevancy" of the tasks. There were many sad songiduring the course relating to "repeats" on experiments, hut the final report by students was an overwhelming approval of the teaching method, the content, and the rigor. It is interesting to note,
Table 1. The Experiments Used Title
Prerequisite
1. Balance
NO
Use of Mettler Balance, weighing by difference. liquids, solids, use of weighing bottle. Project: 6 mai dm-3 H2S04sample weighed into E. Flask. Sample of NsHCO. weighed by difference into the HzSD4. Final mass of solution determined.
From reported mass of HtSO1. NaHCDs final solution mass calculafed.
2. Volumetric Glassware
NO
Use of transfer, seriological pipet and volumetric flasks. Ripsing techniques, transfer of solids to Vol. flasks, use of pipetting bulbs. Project: A vqlume of H2SO4solytion was diluted to 50 cm3. Aliquots of this were submitted. Techniques of calculating how to make required dilutions. Project: Two different serial dilutions required. Aliquots submitted. Simple programming. We used "Wang" system but will use both this and PDP-6 next year. Debugging technique. Project: A program was written.
Entire Aliquot wgs titrated.'
3. Serial Dilution
2
4. Computer Piogramming
NO
5 Graphong
No
6. Titration
1.2
7. Spectranic 20
3, 5
8. Buffer
1, 2. 3. 6
Brief Description
Proqrammeo mate, a1 on now lo preparc graphs roth approDrnale axos troal and error anempt t o p ot f w c t onr y olamg lonear relawmzh ps. evu mtmn 01 mercapts an0 slopes Pro ecl Analyze a table of data. Use of buret, theory of end point, back titration, rinsing. Project: Standardization of NaOH: determine molecular weight of an acid. Use of spectral instruments, mechanics of and terminology. Project: Spect!~of e compound was determined and the absorptivity evaluated. Students were given a very brief direction on how to prepare buffer of specific pH. Project: Buffer was oreoared and submitted.
,here experiments have now been modified. A dye stod solution is diiuted and grading is done spectrophotometricaiiy
616 I
Jovrnal of Chemical Education
Grading Technique
Titrations Value of X keyed and the value of Y calculated by Student program found. Era "at on a1 slopes and
nterccpts Accuracy of molecular weight. hmax. tmax evaluation pH meter
that t h e faculty is a h i t uneasy a b o u t the laboratory course because t h e y h a d so little to do!!! Appendix: Laboratory Examination 1) This examination will be givenduring the week of Dec. -t o . You are t o schedule your exam on one of four afternoons. You will need to have the time from 130-5:00 p.m. available. Schedule sheets will be available in your class; only 20 persons per day will be scheduled. 2) On the day your examination is scheduled, you should be in S-301 by 1 3 0 p.m. At that time you will be given Part 1of the exam; attached is a copy of the four types of questions you will be asked to complete. (Closed Book.) 3) When you have completed Part 1, you will then go to S-305 and select a number by random. That number will indicate which one of the four possible laboratory exams you will take; the attached sheet gives the directions for these four experiments. Experiments will be graded for accuracy. (Laboratory Notebooks may be used.)
Part 1. Chemistry Laboratory Examination: Questions similar to the following will be asked. 1) From titration data, calculate the molecular weight of a monopratie acid. 2) Given the following table of data, write an equation which best correlates the information. Evaluate the slope and intercept. 3) Write a computer program to solve the following equation 4 ) Using only 5, 10.25 cm"ipets
and 50 and 100 cm3 vvol flasks, tell how to prepare a solution which is 1.10-'mol dm-"from a stock solution which is 1.0 mol dm-a.
Part 2. You will select, by lot, one of the following practical laboratory experiments. 1) Titrations A standard NaOH solution (molarity given on the bottle) and a solid unknown acid will be provided. Determine the molecular weight of the unknown aeid;HX, HX
+ NaOH
-
NaX
+ H20
Stations to be equipped with: 50em3 burets, five 125 cmWflasks, wash bottle filled, indicator, towel, spatula, weighing bottle with unknown acid, funnel, 250 cm3 beakers, standard NaOH solution. Report Sheet. Report Sheet: Mass HX Name ml NaOH Station No. MW,.I, Molarity NaOH-
Table 2. Student Data for 1978 Total students oriainallv ,enrolled Total students completing course % students successfully completing 8 projects Average projects completed successfully % students with perfect practical exam score Average % practical exam score 1% of 6 0 ) % students with 95% or better written exam Averase % written exam score ( % of 401
94
2) Buffer A standard NaOH solution (molarity given an bottle) and a solid salt will be provided. From directions provided, prepare 1W cm3 of a buffer with the pH requested. Stations will be equipped with: two 1M1c m v o l flasks, two 100 cm%eakers, capillary pipets, wash bottle filled with H 2 0 distilled, weighing battle with solid salt (labeled), NaOH solution, 1, 5, 10, and 25 em" pipets, 10 cm3 serological pipets, buret, funnel, spatula, towel, labels, pipet bulb. Report Sheet: Turn in Name labeled buffer solution. Station No-. Molarity NaOHAssigned pH , ------A solution of adye will be provided (concentration in g l c d a n d MW of dye will be given on label). You are to sketcha spectrum of the compound and determine the extinction coefficient a t the wavelength of minimum 90transmission. Stations will be equipped with: two 100 and 250 c d v o l flasks, 1, 5, 10, and 25 cm" pipets, beaker, funnel, capillary pipet, 2 sheets of graph paper, 4 Speetronic 20 test tubes, 1 Speetronic 20, a pipet bulb, towel, wash battle, stoppers. Name Report Sheet: Absorptivity = (give units) Station No.Conc. of dyeX max (wavelength of minimum % T ) 4) Serial Dilution Two standard solutions, A and B. will be provided. A 1:1000 dilution of solution A and a 1:250 dilution of B is to be made. Then a 10 cm%ample of A and 5 cm:' sample of B are to be mixed and diluted to 50 cm? with distilled water. Stations will be equipped with: a pipet bulb, three 50 em:' and three 100 cm3 vol flasks, 1,5,10,25 cdpippets, a svlution of A and a solution of B, funnel, wash bottle with distilled water, stoppers for vol flasks, labels. Report Sheet: Turn in with labeled Name final (A + B) solution. Station No.-
Volume 56. Number 9, September 1979 ! 617
