Transcript Rethinking Quant The Importance of Analytical Thinking

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
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A Plea for Rationally Coordinated Courses in Analytical Chemistry (Brinton, 1924)
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The Training of Analysts (Clarke, 1937)
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Developments in the Teaching of Analytical Chemistry (Picketts, 1943)
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Analytical Chemistry – How It Should be Taught (Bremner, 1951)
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Education Trends in Analytical Chemistry (Symposium, 1960)
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Present Status of the Teaching of Analytical Chemistry (Symposium, 1979)
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We Analytical Chemistry Teachers Don’t Get No Respect (Hirsch, 1987)
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Keeping a Balance in the First Analytical Course (Kratochvil, 1991)
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Teaching Analytical Chemistry in the New Century (Symposium, 2001)
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What is the Role of the Quant Course?
Is it to…
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…develop a fundamental understanding of
equilibrium chemistry and laboratory skills
in solution chemistry?
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…study modern, instrumental analytical
techniques and applications?
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…learn to solve real problems and to work
as part of a small research team?
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Other Factors Affecting the
Design of the Quant Course
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Institutional Resources
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Student Profile
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available instrumentation
computational technology
operating budget
academic strengths and weaknesses
balance between majors and non-majors
career goals
Departmental Curricular Needs
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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?
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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
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Advanced Inorganic Chemistry Instrumental Analysis
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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
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Institutional, Departmental,
and Student Context
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Institution
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Department
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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
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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
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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
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Chem 260: Class
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Structural Detail
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Main Topics
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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
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ladder diagrams for visualizing equilibrium chemistry
data analysis exercises
 uncertainty in measurements
 statistical comparison of data sets
 modeling data
 outliers
pre-lab planning time
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Chem 260: Lab
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Structural Detail
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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
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Case Studies in Ethics (1 week)
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Four Preliminary Labs (4 weeks)
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introduce instrumentation, software, and important analytical concepts
detailed procedures provided
focus on communicating results
Four 2-3 Week Project Labs (9 weeks)
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no (or minimal) procedure provided
statement of goals and issues to consider
students design experiment
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Preliminary Labs (and Analytical Content)
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Preparing Solutions
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Newton’s Law of Cooling
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fitting theoretical models to data
significance testing
Determination of Acetic Acid in Vinegar
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uncertainty in measurements
summary statistics
pH calibration and measurement
acid-base titrations
primary vs. secondary standards
Characterizing an Oscillating Reaction
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Beer’s law
calibration using external standards
boxcar filters and ensemble averaging
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Project Labs (with goals)
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Decomposition of H2O2
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Thermodynamics of Ca(OH)2 Solubility
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determine DG, DH, and DS for the solubility reaction
determine the effect of temperature on solubility
Acid Dissociation Constants of Organic Dyes
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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
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determine rate law for the reaction
explore the effect of pH on the reaction’s rate
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Newton’s Law of Cooling
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Prior to lab
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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
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T(t) = T0 + (T0 – Ts)e-kt
two temperature probes
five trials with each
variable initial temperatures
Data Analysis
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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
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Confusion with Error Analysis
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an average Ts of 23.19oC with a standard
deviation of ±0.58oC is not in agreement
with an expected value of 22.7oC
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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
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data analysis exercise on comparing data
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Data Analysis Exercise on Regression
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Geometer’s Sketchpad
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Anscombe data sets
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warming of cold probe
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cooling of warm probe
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Project lab on bleaching
of dyes
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Characterizing an Oscillating Reaction
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ostensible goal for students is to
follow the BZ oscillating reaction
spectrophotometrically
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practical goal is to provide an
introduction to visible spectroscopy
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signal-to-noise ratio
ensemble averaging
boxcar smoothing
Beer’s law
external standards calibration curves
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Project Lab 1
Thermodynamics of the Decomposition of H2O2
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Project Goals
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What is the value of DH for the reaction?
Demonstrate experimentally that the role of Fe3+ is catalytic.
Issues to Consider
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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?
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Verifying that Fe3+ is not Consumed
During the Decomposition of H2O2
each spectrum is average of 16 scans
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Project Lab 3
Acid Dissociation Constants for Organic Dyes
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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.
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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
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Anthocyanin Dye in Cranberry Juice
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Student Response
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“I liked that way we tied the labs in with the
class…it helped me understand the material.”
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“[The course] bridged the gap between chemistry
in the lab and chemistry in the classroom.”
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“Labs really pushed my critical thinking and
writing abilities…I liked the way [the course]
flows…everything is connected.”
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“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.
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Acknowledgments
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Camille and Henry Dreyfus Foundation
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DePauw University
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Nicole Sweet (DPU ’04)
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Sharon Crary
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Chem 260 students
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