Teaching Students to Think as Analytical Chemists教学生为分化学家认为

1、teaching students to think as analytical chemistsdavid harveydepartment of chemistrydepauw universitypapers/symposia on education in analytical chemistry from journal of chemical educationa plea for rationally coordinated courses in analytical chemistry (brinton, 1924)the training of analysts (clark

2、e, 1937)developments in the teaching of analytical chemistry (picketts, 1943)analytical chemistry - how it should be taught? (bremmer, 1951)education trends in analytical chemistry (symposium, 1960)present status of the teaching of analytical chemistry (symposium, 1979)we analytical chemistry teache

3、rs dont get no respect (hirsch, 1987)keeping a balance in the first analytical course (kratochvil, 1991)teaching analytical chemistry in the new century (symposium, 2001)what is the role of undergraduate analytical chemistry?to develop fundamental understanding of equilibrium chemistry and laborator

4、y skills in solution chemistry?what is the role of undergraduate analytical chemistry?to develop fundamental understanding of equilibrium chemistry and laboratory skills in solution chemistry?to study modern, instrumental analytical techniques and applications?what is the role of undergraduate analy

5、tical chemistry?to develop fundamental understanding of equilibrium chemistry and laboratory skills in solution chemistry?to study modern, instrumental analytical techniques and applications?to learn to solve real problems and to work as part of small research team?on the importance of equilibrium a

6、nd solution chemistry“titrations are still the best way of obtaining rapid, parts-per-thousand precisionand are still of importance in industry and commerce.”b. kratochvil j. chem. educ., 1991, 68, 838-839on the importance of modern analytical chemistry“the greatest single pedagogical change is the

7、impact of instrumental methodsundergraduate instruction in modern methods of analysis is becoming an educational responsibility.”p. w. west j. chem. educ., 1952, 29, 222-223on the importance of providing real analytical problems“in summary, chemical analysis is an applied science. the teaching of th

8、e field must imbue the applied aspects in the student, and this can best be done by using real situations.s. siggia j. chem. educ., 1967, 44, 545-546other factors at play in designing courses in analytical chemistrydepartmental resourcesninstrumentationncomputational technologynbudgetother factors a

9、t play in designing courses in analytical chemistrydepartmental resourcesninstrumentationncomputational technologynbudgetdepartmental curricular needs nwhere/how is equilibrium chemistry covered?ninstrumental analysis lab vs. advanced multidisciplinary labother factors at play in designing courses i

10、n analytical chemistrydepartmental resourcesninstrumentationncomputational technologynbudgetdepartmental curricular needs nwhere/how is equilibrium chemistry covered?ninstrumental analysis lab vs. advanced multidisciplinary labprofile of studentsnacademic strengthnmotivationncareer goalsone thing up

11、on which we all agree there isnt enough time“how can the professor reap the benefits of teaching fundamentals while bringing in elements of problem-based learning without compromising the former? available time is a very serious constraint. the entire formal lecture time in undergraduate analytical

12、chemistryis about two and one-half solid 40 hour weeks; laboratory time is equivalent to three to four weeks. wow! thats not much!” r. w. murray anal. chem. 1998, 70, 425aone thing upon which we all agree there isnt enough time“how can the professor reap the benefits of teaching fundamentals while b

13、ringing in elements of problem-based learning without compromising the former? available time is a very serious constraint. the entire formal lecture time in undergraduate analytical chemistryis about two and one-half solid 40 hour weeks; laboratory time is equivalent to three to four weeks. wow! th

14、ats not much!” r. w. murray anal. chem. 1998, 70, 425a“the demands upon a students time in the study of science are growing more severe each year as the field broadens and the number of subjects necessary to master in that field increases.” h. m. p. brinton j. chem. educ. 1924, 1, 226-230 ifnumber o

15、f topics available time an educational proposition!ifnumber of topics available time thenour goal must be to prepare a student to learn on his or her ownan educational proposition!ifnumber of topics available time thenour goal must be to prepare a student to learn on his or her ownbyteaching our stu

16、dents to think as analytical chemistsan educational proposition!can we teach students to think as analytical chemists?“can we teach analytical thinking? the answer is that we cannot. it is a thought process and each individual has a varying thought process. however, we can exercise the students thou

17、ght processes by continually exposing him or her to real analytical problems during the course of his or her education.”s. siggia j. chem. educ., 1967, 44, 545-546creating an environment that encourages students to “think as analytical chemists”what do we mean by “real analytical problems”?nrealisti

18、c samples (“all the world is a sample”)nrealistic issues in experimental designcreating an environment that encourages students to “think as analytical chemists”what do we mean by “real analytical problems”?nrealistic samples (“all the worlds a sample”)nrealistic issues in experimental designdevelop

19、 and implement curricular strategies for increasing intuitive, critical thinking:nhave students critique analytical methods nprovide opportunities for “back of the envelope” approximationsnprovide unexpected outcomesanalytical chemistry curriculum at depauw universityas part of common introductory c

20、orenchem 260: thermodynamics, equilibrium, and kinetics (lab emphasis)courses in analytical chemistrynchem 351: chemometricsnchem 352: analytical equilibria and separationsnchem 353: instrumental methodsnchem 450: method development (lab course)critiquing analytical methodsdetermination of total iro

21、n in water and wastewaterfor samples containing less than 2 ppm fe, directly transfer a 50-ml portion to a 125-ml erlenmeyer flask. samples containing more than 2 ppm fe must be suitably treated before acquiring the 50-ml portion. add 2 ml of concentrated hcl and 1 ml of hydroxylamine to the sample

22、in the erlenmeyer flask. heat the solution to boiling and continue boiling until the solutions volume is reduced to between 15 and 20 ml. after cooling to room temperature, transfer the solution to a 50-ml volumetric flask, add 10 ml of an acetate buffer, 2 ml of a 1000 ppm solution of o-phenanthrol

23、ine, and dilute to volume. allow 10-15 min for color development before measuring the absorbance at 510 nm, using a blank prepared by carrying 50 ml of distilled water through the same procedure.critiquing the analytical methodwhy are there different directions for treating the sample depending on t

24、he amount of fe present? what is meant by the statement that samples “containing more than 2 ppm fe must be suitably treated”?what is the role of hydroxylamine in this procedure and why is such a large excess added?why is it necessary to adjust the ph using an acetate buffer?why is it necessary to w

25、ait 10-15 min before measuring the absorbance?the acetate buffer is prepared using ammonium acetate and glacial acetic acid. given that even high-quality ammonium acetate is contaminated with iron, why isnt this a source of interference for this analysis?making use of “back of the envelope” approxim

26、ationschoosing an analytical methodproblem: using an acid/base titration, can you find the concentration of a weak acid with a pka of 3 and a nominal concentration of 75 mm in the presence of a weak acid with a pka of 7 and a nominal concentration of 25 mm. assume a sample of 5 ml and a titrant that

27、 is 0.01 m naoh. choosing an analytical method: a “back of the envelope” exercisechoosing an analytical method: a “back of the envelope” exercisechoosing an analytical method: a “back of the envelope” exercisechoosing an analytical method: a “back of the envelope” exerciseoptimizing a separationprob

28、lem: find conditions for separating the following mixture by capillary zone electrophoresis:n2-aminobenzoic acid (pka1 = 2.08, pka2 = 4.96)nbenzylamine (pka = 9.35)n4-methylphenol (pka = 10.26)optimizing a procedure:a “back of the envelope” exerciseproviding an unexpected resultselecting an appropri

29、ate sample“the weakest link exercise”, settle, f. a.; pleva, m. anal. chem. 1999, 71, 538a-540a.students analyze corn chips for na and evaluate contributions of sampling, sample preparation, and measurement technique to overall variance using a nested experimental design.students predict sampling to

30、 be the weakest link.result sampling identified as the weakest link (accounting for approximately 80% of overall variance).selecting an appropriate sample:providing an unexpected outcomesample: erythrosine b coated on nacl.students predict that sample preparation is the weakest link; they do not con

31、sider sampling to be important because sample appears homogeneous.selecting an appropriate sample:providing an unexpected outcomeresult sampling is weakest link (accounting for approximately 98% of overall variance).benefits unexpected outcome encourages greater appreciation for and awareness of imp

32、ortance of sampling; students discover that their ability to prepare samples is better than they expected.developing an analytical methodproblem: develop a spectrophotometric method for determining the concentration of p-nitrophenol in aqueous environmental samples.developing an analytical methodpro

33、blem: develop a spectrophotometric method for determining the concentration of p-nitrophenol in aqueous environmental samples.approach of a typical beginning student might be:nprepare an external standards calibration curvenevaluate the calibration curves linearitynrun a standard sample and evaluate accuracy nanalyze unknowns and report resultsdeveloping an analytical method: providing an unexpected outcomedeveloping an analytical method: providi