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Rethinking Quant: The Importance of Analytical Thinking David Harvey Percy L. Julian Professor Chemistry & Biochemistry DePauw University Greencastle, IN [email protected] Papers/Symposia on Education in Analytical Chemistry in the Journal of Chemical Education A Plea for Rationally Coordinated Courses in Analytical Chemistry (Brinton, 1924) The Training of Analysts (Clarke, 1937) Developments in the Teaching of Analytical Chemistry (Picketts, 1943) Analytical Chemistry – How It Should be Taught (Bremner, 1951) Education Trends in Analytical Chemistry (Symposium, 1960) Present Status of the Teaching of Analytical Chemistry (Symposium, 1979) We Analytical Chemistry Teachers Don’t Get No Respect (Hirsch, 1987) Keeping a Balance in the First Analytical Course (Kratochvil, 1991) Teaching Analytical Chemistry in the New Century (Symposium, 2001) 2 What is the Role of the Quant Course? Is it to… …develop a fundamental understanding of equilibrium chemistry and laboratory skills in solution chemistry? …study modern, instrumental analytical techniques and applications? …learn to solve real problems and to work as part of a small research team? 3 Other Factors Affecting the Design of the Quant Course Institutional Resources Student Profile available instrumentation computational technology operating budget academic strengths and weaknesses balance between majors and non-majors career goals Departmental Curricular Needs Where is equilibrium chemistry covered? Is there a dedicated advanced analytical lab? Is the analytical class a service course? Institutional commitment to vocational training? How does the department meet the CPT guidelines? 4 Analytical Chemistry at DePauw University Before Fall 2001 Recommended Curriculum for a Chemistry Major Year Fall Spring 1 Principles of Chemistry I Principles of Chemistry II 2 Organic Chemistry I Quantitative Analysis Organic Chemistry II Inorganic Chemistry 3 Physical Chemistry I Physical Chemistry II 4 Advanced Inorganic Chemistry Instrumental Analysis 5 Analytical Chemistry at DePauw University Beginning Fall 2001 Chem 120: Structure & Function of Organic Molecules Chem 130: Structure & Properties of Inorganic Compounds Chem 170: Stoichiometric Calculations Chem 240: Structure & Function of Biomolecules Chemical Reactivity Chem 260: Thermodynamics, Equilibria, and Kinetics Chemical Analysis Chem 351: Chemometrics Theoretical and Computational Chemistry Chem 352: Analytical Equilibria Chem 353: Instrumental Methods Chem 450: Method Development Lab 6 Institutional, Departmental, and Student Context Institution Department private, undergraduate, residential university 2400 students very selective 8.33 full-time faculty (1.33 in analytical) 80 declared majors (8 chemistry, 72 biochemistry) excellent operating budget and institutional support strong instrumentation in all major areas Student Audience 24 students/section; 3 sections/year ~50% of students are chemistry or biochemistry majors ~70% fulfilling requirements for health science programs ~10% are first-year students and ~20% are juniors or seniors 7 Course Philosophy …to create an environment that develops a student’s capacity to look at problems through the lens of analytical chemistry; that is, to think as an analytical chemist? “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 student’s thought processes by continually exposing him to real analytical problems during the course of his education.” S. Siggia J. Chem. Educ. 1967, 44, 545-546 8 Chem 260: Class Structural Detail Main Topics class: 14 weeks at 3 x 60 minutes “Big 3” topics are foundational to analytical chemistry additional topics common to “Principles of Chemistry II” are left to other courses 8-10 days available to focus on additional analytical content Additional Analytical Content ladder diagrams for visualizing equilibrium chemistry data analysis exercises uncertainty in measurements statistical comparison of data sets modeling data outliers pre-lab planning time 9 Chem 260: Lab Structural Detail lab: 14 weeks at 1 x 180 minutes team of three students instrument suite: Vernier LabPro data interface with pH, ORP, temperature probes and drop counter; Ocean Optics USB-2000 visible spectrometer data stored on network drive Case Studies in Ethics (1 week) Four Preliminary Labs (4 weeks) introduce instrumentation, software, and important analytical concepts detailed procedures provided focus on communicating results Four 2-3 Week Project Labs (9 weeks) no (or minimal) procedure provided statement of goals and issues to consider students design experiment 10 Preliminary Labs (and Analytical Content) Preparing Solutions Newton’s Law of Cooling fitting theoretical models to data significance testing Determination of Acetic Acid in Vinegar uncertainty in measurements summary statistics pH calibration and measurement acid-base titrations primary vs. secondary standards Characterizing an Oscillating Reaction Beer’s law calibration using external standards boxcar filters and ensemble averaging 11 Project Labs (with goals) Decomposition of H2O2 Thermodynamics of Ca(OH)2 Solubility determine DG, DH, and DS for the solubility reaction determine the effect of temperature on solubility Acid Dissociation Constants of Organic Dyes determine DH for reaction verify that Fe3+ is acting as a catalyst determine pKa for synthetic and/or natural organic dyes Kinetics of the Bleaching of Dyes determine rate law for the reaction explore the effect of pH on the reaction’s rate 12 Newton’s Law of Cooling Prior to lab in-class data analysis exercise on measurement uncertainty lab experiment evaluating accuracy and precision for dispensing 10 mL of reagent using various types of glassware Experimental Details T(t) = T0 + (T0 – Ts)e-kt two temperature probes five trials with each variable initial temperatures Data Analysis model data using y = Ae-Ct + B determine values for for T0, Ts, and k compare expected values to determined values compare two probes evaluate appropriateness of Newton’s law 13 Confusion with Error Analysis an average Ts of 23.19oC with a standard deviation of ±0.58oC is not in agreement with an expected value of 22.7oC an average Ts of 23.19oC (±0.58oC) with one probe is not the same as an average Ts of 22.38oC (±0.55oC) for a second probe data analysis exercise on comparing data 14 Data Analysis Exercise on Regression Geometer’s Sketchpad Anscombe data sets warming of cold probe cooling of warm probe Project lab on bleaching of dyes 15 Characterizing an Oscillating Reaction ostensible goal for students is to follow the BZ oscillating reaction spectrophotometrically practical goal is to provide an introduction to visible spectroscopy signal-to-noise ratio ensemble averaging boxcar smoothing Beer’s law external standards calibration curves 16 Project Lab 1 Thermodynamics of the Decomposition of H2O2 Project Goals What is the value of DH for the reaction? Demonstrate experimentally that the role of Fe3+ is catalytic. Issues to Consider To determine whether there is a relationship between two variables you must ensure that all other variables remain fixed. A calorimeter will absorb some of the heat released during the reaction. You will need to establish if the amount of heat absorbed by your calorimeter is significant and, if so, determine how to make an appropriate correction. What are the properties of a catalyst? In determining a value for DH you inevitably will make some assumptions. What assumptions might you make? How can you minimize their impact on your analysis? 17 Verifying that Fe3+ is not Consumed During the Decomposition of H2O2 each spectrum is average of 16 scans 18 Project Lab 3 Acid Dissociation Constants for Organic Dyes Project Goal Determine the pKa of two organic dyes by adapting the procedure from G. G. Patterson, “A Simplified Method for Finding the pKa of an Acid-Base Indicator by Spectrophotometry,” J. Chem. Educ., 1999, 76, 395-398. 19 Using Ladder Diagrams to Foster Intuitive Thinking • class: simplify equilibrium problems, such as pH dependent solubility of CaF2 • lab: control the speciation of weak acids by controlling pH F– pH 4.17 pH = pKa = 3.17 Buffer Region 2.17 HF HPLC retention of p-aminobenzoic acid 20 Anthocyanin Dye in Cranberry Juice 21 Student Response “I liked that way we tied the labs in with the class…it helped me understand the material.” “[The course] bridged the gap between chemistry in the lab and chemistry in the classroom.” “Labs really pushed my critical thinking and writing abilities…I liked the way [the course] flows…everything is connected.” “I have learned a lot in this class…on the whole, I have gained a sense of clarity, and dare I say confidence. Confidence to know that if I don’t get something, I can figure it out. 22 Acknowledgments Camille and Henry Dreyfus Foundation DePauw University Nicole Sweet (DPU ’04) Sharon Crary Chem 260 students 23