This investigative case module was prepared as part of a BioQUEST faculty development workshop. The cases, resources, and implementation strategies were developed by participants for use with their own students. We invite you to adopt and adapt the following materials.

The BioQUEST Curriculum Consortium is committed to the reform of undergraduate biology instruction through an emphasis on engaging students in realistic scientific practices. This approach is sometimes characterized as an inquiry driven approach and is captured in BioQUEST's three P's (problem-posing, problem-solving, and peer-persuasion). As part of this workshop groups of faculty were encouraged to initiate innovative curricular projects. We are sharing these works in progress in the hope that they will stimulate further exploration, collaboration and development. Please see the following links for additional information:

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Investigative Cases
The Case: What Happened to Our Friend Ted?

Oh, Ben, this is a sad story about our friend Ted. Four days ago, his wife found him dead in his bed after having dinner. There is a rumor in town that she probably poisoned him.

Last night, I talked to Angela, Ted's wife. She said that he was a heavy salad eater and always used plenty amounts of his favorite dressing, Vidalia Ranch. To save money, she said that she made the Vidalia Ranch dressing for him in a large quantity about a month ago. Ted was active and healthy before his death. He had his annual check up and his blood work was excellent. Angela said that they have been together every single day after he was laid off from work a week ago. They dined together mostly at home. The only thing they did differently was that she prefers commercial dressings over the homemade Vidalia Ranch dressing.

When I asked her if she thought eating all that Vidalia Ranch dressing was a possible cause for his death, she admitted that the homemade salad dressing started to have a noticeable bad odor and it seemed possible.

What do you think, Ben?

Case Author:
Paulos Yohannes Georgia Perimeter College

Case Analysis

Why are metal ions essential to the normal biochemical activity of living things?

What is the difference between the commercial and the homemade salad dressing?

What is the chemical that could have prevented this death?

Option: Include a know / need to know chart like the one below:

What do you know?
What do you need to know?

Learning Goals


The students will learn the importance of metal ions in living organisms.

The students will learn that we can use chelating reagents to effectively remove metal ions in solution.

The students will be able to understand the chemistry (structure and function) of chelating reagents.

The students will be able to learn the thermodynamics of metal-ligand complexation.

The students will be able to do titration experiments to determine quantitatively the amount of divalent metal ions in solution.



Investigations and Activities

In groups of 2 or 3 students will discuss about the significance of metal ions in Biology.

Research and report to the cause of the odor in the salad dressing. Write a statement that relates to what happened to the salad dressing.

Classroom activity on the chemistry (structure and activity) of EDTA, the food preservative.

Classroom discussion on the thermodynamics of metal complex formation.

Chemistry workbench on the titration of metal ions using EDTA and generating standard curves.

Titration of a sample of home-made salad dressing prepared by students and commercial product and determining the total metal ion concentration.



General information

General Chemistry : Ebbing, D and Gammon, S. 7th ed. Houghton Mifflin, 2002.
Biochemistry: Wiley, 1995. Voet, J and Voet, D.
Chemical Ingredients of Food Products


EDTA V a food additive sequesterant:
EDTA: www.
EDTA Titration Lab:

Experimental Procedure:
Determination of Ca-Mg by EDTA Titration:

Students will usually obtain additional references or resources
to help answer or explore their questions.

Special Data Items

1. MEDTA.gif
2. MEDTAb.gif
3. ranch.gif
4. titration.jpg


Student Products

A short report what you know and what you need to know on the case.

The need of EDTA in a commercial salad dressing V a chemist perspective

A forensic report on the experiment performed V include V procedure, theory, data, result, discussion and conclusion.

Standard curve.

Assessment and Evaluation Plan

Logic used to analyze the case (20%)
Report on the role of metal ions in Biology (10%)
A report discussing the chemistry of Metal ion-EDTA complexation (20%)
Standard Curve data (10%)
Experimental Lab report (40%)



Course name:
Principles of Chemistry for Honors
Likely sequence in syllabus:
After thermodynamics V Coordination Chemistry V special topic for Chemistry Majors
Time during term:
The last four weeks of the semester
Four weeks
Lab, Classroom, modeling software and some distance learning
Students in course:
Chemistry majors - honor students
Collaborative elements:
Work in groups, Share access to resources, Likely to discuss cases outside of class
Additional notes:



Models of EDTA

Titration Apparatus

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