Assessment in Analytical, General, Organic & Physical Chemistry

 

Assessment of Lecture-Laboratory Connections in Introductory General Chemistry

Ted M. Pappenfus, Assistant Professor of Chemistry

November 30, 2006

 

General Chemistry I and II at the University of Minnesota, Morris (UMM) are introductory chemistry courses with corequisite labs.  Each course meets the general education requirement of a science course with lab (Sci-L).  The two courses together are designed to prepare a student for a major in science, including chemistry and biology.  This course introduces the basic skills and concepts needed for further study of chemistry.  Students learn to reason and describe the physical world as chemists do.  A major task is to attain proficiency in problem solving and laboratory skills for the application of chemical concepts.  The course also delves into the description of matter on the subatomic, atomic, and molecular levels paying attention to how this relates to trends in the properties of substances.

 

Chemistry faculty at UMM have made great efforts to better correlate lecture and laboratory material in general chemistry courses.  When lab and lecture components are taught independently without concurrent concepts, student learning becomes less efficient and frustrating for both the student and instructor.  To gauge the effectiveness of our efforts to make connections between lab and lecture in our general chemistry courses, we have utilized carefully designed lecture exam questions to assess student understanding of laboratory experiences.  This assessment was conducted in the fall of 2006.  Enrollment for the lecture course was approximately 80 students.  The number of these students that were included in the study for each exam varied.  Four lab-lecture examples are outlined in this summary.

 

Example one.  The first experiment of the semester includes an introduction of several common laboratory techniques.  Included in the lab are concepts of density and significant figures.  These concepts are also covered extensively in lecture.  In this experiment, students construct a micropycnometer (a device used to measure the density of a liquid) and use density calculations to determine its volume.  Assessment of this laboratory experience was conducted by including the following exam question in the first lecture exam:

 

                  Britney Spears decides to give up her music career and becomes a chemistry major at UMM.  After preparing her micropycnometer in her first general chemistry lab, she decides to determine its volume with ethyl alcohol (d = 0.7901 g/mL).  Britney collects the following data in her notebook:

 

                                   *Mass of empty micropycnometer = 5.493 g

                                   *Mass of micropycnometer and ethyl alcohol = 6.392 g

 

           What is the volume of BritneyŐs micropycnometer?

 

a.

0.899 mL

b.

1.14 mL

c.

1.138 mL

d.

0.710 mL

e.

0.7103 mL

 

The question mimics the lab experience with the exception that an alternative liquid with a unique density is used to calculate the volume of the micropycnometer.

 

The results of student responses to this question are given below:

The correct answer to the question is B.  As indicated above, only one-third of the class answered correctly.  If significant figures are ignored, both B and C become acceptable answers.  As a result, it appears that 91% of the students understood the concept of density, but only a third of the students fully understood the rules for significant figures. 

 

How can this data be used to improve student learning?  This data is not completely surprising as rules for significant figures are challenging for students.  To improve student understanding of these rules, laboratory reports throughout the remaining semester were graded on the proper application of these rules.  Although no concrete data has been compiled, student performance on significant figures has improved this semester.

 

Example two.  The fourth experiment of the semester includes the synthesis and analysis of aspirin.  The underlying concepts included in this experiment are limiting reagents and percent yield.  Both concepts were discussed at length in lecture.  Assessment of this laboratory experience was conducted by including the following exam question in the second lecture exam:

 

                  Aspirin is produced by the reaction of salicylic acid and acetic anhydride.

 

C7H6O3(s) + C4H6O3(l) ¨  C9H8O4(s) + C2H4O2(l)

 

If you mix 5.00 grams of each reactant, how many grams of aspirin can theoretically by obtained?

 

a.

2.83 g

b.

3.83 g

c.

6.52 g

d.

8.82 g

e.

10.0 g

 

 

 

The question accurately reflects the laboratory experience with the exception that different amounts of reagents were used in the actual lab experience.

The results of student responses to this question are given below:

The correct answer to the question is C.  It appears the vast majority of students understood the concepts of limiting reagents and percent yield.  These are recurring concepts throughout the course and student understanding likely improves.

 

Example three.  The sixth experiment in the course includes quantitative analysis of household vinegar with the use of analytical titrations.  Concepts included in this experiment are acid-base chemistry and solution stoichiometry.  These concepts are discussed at length in lecture.  Assessment of this laboratory experience was conducted by including the following exam question in the third lecture exam:

 

                  A 25.00 mL sample of NaOH is titrated with 17.13 mL of 0.3150 M HCl. What is the concentration of the NaOH solution?

 

a.

0.001360 M

b.

0.1233 M

c.

0.2158 M

d.

0.4597 M

e.

0.7356 M

 

 

 

The question is very similar to the lab experience except a different acid standard was used in the actual lab to determine the NaOH concentration.  The results of student responses to this question are given below:

The correct answer to the question is C.  This data suggests students understood the concepts of solution stoichiometry and acid-base chemistry.

 

Example four.  The ninth experiment of the semester introduces students to spectroscopy.  Included in this experiment is the determination of energies and intensities of the transistions present in hydrogen line emission spectra.  Students experimentally measure the energies and then calculate the values based on the Bohr model of the hydrogen atom.  This treatment of the atom is also discussed at length in lecture.  Assessment of this laboratory experience was conducted by including the following exam question in the fourth lecture exam:

 

                  For a hydrogen atom, calculate the wavelength of the line in the Lyman series that results from the transition n = 4 to n = 1.

a.

30.4 nm

b.

97.2 nm

c.

114 nm

d.

121 nm

e.

182 nm

 

This question is very similar to the lab experience with the exception that a different series (Balmer series) was analyzed in the actual lab.  The results of student responses to this question are given below:

The correct answer to the question is B.  Students had much difficulty with these calculations in the actual lab, so the exam data is encouraging and suggests that the lab experience facilitated student learning.

 

Summary:  The data presented in this report suggest that positive connections are being made between the lab and lecture components of our introductory chemistry course.  The efforts of our faculty to better correlate lab and lecture material have promoted student learning in this course.  Deficiencies in our methods have been measured and addressed to improve the efficiency of student learning.

 

Assessment -- Chem 3101 Analytical Chemistry -- Fall 2006

 

Learning Objectives:

 

1. Understanding multiple ways to represent concentrations of solutions.  Understanding how to convert between units.

 

2. Understanding dilution and density.

 

3. Understanding propagation of uncertainty.

 

4. Understanding pH and pOH and the mathematical relationship between the two.

 

5. Use of correct significant figures.

 

The following question was given as a problem on Exam One.  A problem similar to part A had been assigned as a suggested book problem (Quantitative Chemical Analysis, 7th ed by Daniel C. Harris, Chap 1 Number 33).  The answer to part C does not depend on answers to part A and B.  Parts B and C are similar to questions on graded problem sets.

 

2. (15 points) A. What is the density of a 23.46 ± 0.05 wt \% aqueous KOH solution? Diluting 22.72 ± 0.02 mL of the solution to 1.000 ± 0.003 L gives a concentration of 0.1345 ± 0.0003 M?

 

B. What is the uncertainty in the density?

 

C. What is the pH and pOH of the 1.000 L solution (assume 25ˇC)?

 

Average Score

7.5

 

Std Dev of Average

4.1

 

Score

No. of Students

Percentage of Class

0-5

9

36

6-10

9

36

11-15

7

28

 

From the table we can see that the average score on the question was a mere 50% (passing is 60%) and over one third of the class scored less than 33%.  These concepts are important ones in chemistry and are cumulative which means they continue to show up throughout the course.

 

Feedback: Student exams were returned to them with corrections and comments for this problem.  In class a brief summary of answers was given and students were encouraged to review their exam and set up appointments with questions. Approximately eight students met with me regarding this particular question.  They were again referred to the book problem for additional practice. Unit conversion, significant figures, pH, pOH, and dilution continued to be taught in other applications both in lecture and lab throughout the remainder of the semester.

 

Retesting:  The same question was asked on the cumulative final exam but instead of being worth 15 points it was worth nine.

 

Average Score

5.1

 

Std Dev of Average

2.9

 

Score

No. of Students

Percentage of Class

0-3

6

25

4-6

8

33

7-9

10

42

 

From the table we can see that the average did improve by 6% but is still not passing.  The number of students scoring less than 33% dropped from one third to one quarter.  The number of students scoring in the top 33% improved from 28 to 42%.  It is also the case that this problem was graded `tougher' on the final since it was a repeated question and at a lower point value there was less opportunity for partial credit.  Thus the improvement was perhaps even more than the numbers suggest.

 

 

                                     Physical Chemistry Assessment Project

                                                      Jim Togeas, Fall 2006

 

         Overview. The Second Law of thermodynamics is arguably the most sweeping law in physical theory. We devote the middle six weeks of fall semester to it, and much of what precedes it is simply a prelude to the Second Law. Since my emphasis is on applications, I will assess my physical chemistry studentsŐ ability to apply the Second Law to chemical problems and attempt to use the assessment results to improve their understanding.

 

         Two learning objectives.

         #1. The student should be able to apply the Second Law to phase changes.

         #2. The student should be able to apply the Second Law to chemical changes.

 

         Assessment tool. The assessment tool is comprised of examination questions in which the student must carry out a multi-step calculation using corollaries of the Second Law. Here is a sample problem:

         4) a) Find a numerical value for the equilibrium constant at 298 K for the following reaction:

                                                   .

Use the data in the thermochemical table.

         b) Solid AZ2 and gaseous A are introduced into a flask. At equilibrium some solid remains. Find the mole fractions of A and AZ at equilibrium if T =  298 K and p = 30.0 bar.

 

         A three-step assessment. Step 1) Initial assessment by means of an exam. I will go through the exams to see where students had difficulties. Step 2) Improving student learning. I will describe those difficulties to the class and, as always, invite them to my office to discuss learning issues one-on-one. I will put problems from the exam that proved difficult on a problem set and ask the students to work and submit them for evaluation. Step 3) Final assessment. The final exam will have problems of the same type and I will ascertain whether or not students avoided previous difficulties.

 

         Initial assessment. There were four problems, two on phase changes and two on chemical changes. Sixteen students took the exam. Having evaluated the exams and then reviewed them, I recognized two principal difficulties encountered by students.

         Difficulty #1. Students failed to recognize the scope, that is, the range of validity of a Second Law corollary. This had to do with the two questions on phase changes. Since there were two problems and sixteen people working them, there were thirty-two opportunities to make this error. I saw nine errors[1] of this type for a frequency rate of (9/32) x 100 = 28 %.

         Difficulty #2. Students failed to sufficiently correlate the mathematical analysis with the phase or chemical change. Since there were four problems and sixteen people working them, there were sixty-four opportunities to make this error. I saw fifteen errors[2] of this type for a frequency rate of (15/64) x 100 = 23 %.

         Are these weaknesses cause for alarm? No, the errors were predictable—beginnersŐ mistakes. I warned the students that these were pitfalls that they would encounter, and when they get their exams back theyŐll chide themselves for their Ňfolly.Ó They shouldnŐt. These kinds of Second Law analyses are complex. There are many parts to the analysis and itŐs not surprising that details escape the attention of some students, especially in an exam format.

 

         Improving student learning. I put the four exam questions to be reworked and submitted for evaluation on two different problem sets. On the day that I returned the exams, I pointed out these weaknesses.

 

         Final assessment. On the final, there was one problem on phase equilibrium, where students encountered difficulty number one, and a total of two problems where they encountered difficulty number two.

         Difficulty #1. The problem was optional, but twelve of sixteen students attempted it. Three of them committed the same blunder as before, giving a frequency rate of (3/12) x 100 = 25 %, hardly different from the above. ItŐs a smaller sample, but of course I canŐt claim that learning improved.

         Difficulty #2. There were a total of twenty one opportunities to make this error, but nobody did, so here the frequency rate fell to 0 %. I observed improved student learning.

 

         Something for the future. One thing that I donŐt really know is if students review their old exams to determine where they went wrong. My reaction to the first difficulty was that here were people who didnŐt learn from past mistakes. Does nobody learn from past errors? I donŐt believe that. Some of the people in the class are of the type that donŐt tolerate loose ends in anything that they do. Still, it appears that a few lack focus.

 

                             Assessment Information from Nancy Carpenter

                                              Organic Chemistry at UMM

 

         At the end of academic years 2001-2 and 2002-3, Nancy administered the American Chemical Society standardized examination in organic chemistry. Her students performed about four-to-five percentage points above the national test mean.

 

                                                                       

Year

National Test

Mean

UMM Test

Mean

UMM National

Percentile

2001-2

43.3

48

62

2002-3

38.7

43

66

 

 

        



[1] Eight people used the Clausius-Clapeyron equation in a phase equilibrium problem in which there was no vapor present.

[2] The specific error again is frequent with beginners. Students fail to use the chemical equation to guide their calculation of standard enthalpy and free energy changes from tables of standard enthalpies and free energies of formation.