28 Apr 2014

Coordination complexes and crystal field theory in-class worksheet

In-Class Activity

Submitted by Sarah K. St. Angelo, Dickinson College
Categories
Description: 

This is an in-class activity that I made to help students in my second semester general chemistry course work through some aspects of color and coordination chemistry.  The activity was performed with a demonstration of color for nickel coordination complexes (ligands: water, ethylenediamine, and ammonia). I also included equilibria and thermodynamics as those concepts apply to coordination compounds at the introductory level.  This served as a review of the concepts as well.

Learning Goals: 

1.  Students will demonstrate the relationship between observed colors to absorbed colors in visible spectroscopy.

2.  Students will qualitatively rank crystal field splitting strengths to the absorbed color and therefore rank ligands according to their field strength.

3. Students will use prior experience with concepts of chemical equilibria and chemical thermodynamics to make assertions about stability and driving forces for reaction of several coordination compounds.

4. If the related demonstration is performed at the time of the activity, students will use observations to explain chemical phenomena regarding several related coordination compounds.

Equipment needs: 

None beyond the worksheet unless one of the associated demonstrations (links below) are performed.  If desired, a visible spectrometer could be used to measure the wavelengths of maximum absorbance for a more quantitative approach to ranking the ligands.

Implementation Notes: 

I performed this activity in my second semester general chemistry lecture (38 students).  I made the complexes (excepting the EDTA complex, although I could have made it) for them in class and allowed them to inspect the colors.  Students worked in small groups (2-4students) to complete the worksheet. 

Time Required: 
20-30 minutes depending if live demonstration is included
Evaluation
Evaluation Methods: 

This activity was not collected or graded.  In the future, I would follow up this activity with a quiz question that asks them to perform a similar task for a different coordination complex.

Creative Commons License: 
Creative Commons Licence

Comments

Hi, Sarah,

 
Thank you so much for posting the LO on metal coordination chemistry! It does a great job of bringing together several different topics and asking students to apply thermodynamics to new situations. I'm very impressed that you're able to cover this material in second semester general chemistry!
 
I apologize for the delay in giving you feedback. Below are some suggestions for modifying the LO so that the widest possible audience of VIPEr could use it:
 
1) Could you post a key to the worksheet? It would be helpful to make sure that the answers intended are clear.
 
2) Are the students shown the complexes as a demo? In the solid state or in solution? It wasn't clear from the sheet.
 
3) Please replace all equilibrium arrows. The arrows shown currently are resonance arrows.
 
4) Please add an energy axis to the crystal field splitting diagrams for clarity.
 
If you send me an e-mail when changes have been made and posted to VIPEr, I will promptly look at it.
 
Thanks so much again. I hope you're having a relaxing and productive summer so far!
 
Shirley

 

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