Electron transfer

24 Jun 2013
Evaluation Methods: 

Student performance on Preliminary Questions (PQs) and reports are assessed

Percent yield and percent purity from UV-Vis and titration analyses

Accuracy in completion of table of IR bands/assignments

Answers to Thought Questions

Evaluation Results: 

Percent Yield across two years: average 80%+/-11% for 21 students

Percent Purity via titration analysis in first year: -12% error (less than theoretical); implemented improved estimation of endpoint – see Instructor Notes

Added IR Spectroscopy Tables (given values, and a blank one to fill in on report). Without these 'lead by the nose' guides, students did a poor job demonstrating understanding of the meaning of the IR spectra. This is most likely due to the fact that this is their first exposure to IR spectroscopy (second-semester freshman level).

Description: 

Synthesis of ammonium decavanadate, and analysis via IR, UV-Vis and quantitative titration. Time: 1.5 lab periods

 

Purpose

            The purpose of this lab experiment is to expose students to the synthesis of a colored POM, and to connect the use of standard analytical techniques to this new type of compound. It introduces the use of IR spectroscopy of inorganic materials.

 

Introduction

            Ammonium decavanadate ((NH4)6V10O28•6H2O) is an example of a polyoxometallate (POM). POMs are a large and diverse group, containing various metal cations, including, but not limited to, vanadium, molybdenum, chromium and iron. They are formed spontaneously in solution through what is called ‘self-assembly’. Essentially, they come together in solution through unknown mechanisms. In the lab, we can isolate various POMs by controlling conditions to favor one form over another, by varying concentration, pH or counter-ion. In the phase diagram of vanadates (Figure 1), one can see how varying pH and vanadium concentration can yield monomeric vanadate (VO43-), or POMs containing 2-10 vanadium atoms.

Decavanadate in Geology

            The decavanadate anion occurs naturally in minerals, huemulite Na4Mg2V10O28•24H2O, hummerite (KMg)2V10O28•16H2O, lasalite (NaMg)2V10O28•20H2O , pascoite Ca3V10O28•16H2O, magnesiopascoite Ca2MgV10O28•16H2O, and rauvite Ca(UO2)2V10O28•16H2O, which differ in the cations and amount of hydration. As you can see from Figure 3, the dominant color is yellow-orange. This is due to the presence of the decavanadate anion, which is yellow-orange. All of the vanadium POMs and vanadate are yellow-orange due to charge-transfer bands in the 200 – 500 nm range.

Decavanadate in Biology

            Vanadate (VO43-) is isostructural and isoelectronic with phosphate (PO43-). For this reason, vanadate has found interest with researchers studying the role of phosphate in biological systems, such as in insulin uptake in cells. In addition, decavanadate has been used to bind to biologically relevant molecules, such as gelatin, cytosine, estrogen receptor, and myosin.

 

Laboratory Experiment

In this experiment, students synthesize ammonium decavanadate, and analyze the resulting product via UV-Vis and IR spectroscopy as well as by permanganate titration.

Corequisites: 
Prerequisites: 
Learning Goals: 
  1. The student will define polyoxometallates (POMs).
  2. The student is able to interpret a concentration-pH diagram to determine conditions suitable for formation of the desired product.
  3. The student will apply IR spectroscopy to identify inorganic compounds.
  4. The student will use Beer’s Law to analyze the purity of a colored compound.
  5. The student will use redox titration to analyze a compound for purity.
Course Level: 
Equipment needs: 

Materials for a class of 20:

Ammonium metavanadate (NH4VO3, CAS#7803-55-6, Aldrich 99%): 6.0g

50% acetic acid solution: 100 mL

95% ethanol: 360 mL

Oxalic acid dihydrate (H2C2O4•2H2O, CAS#6153-56-6, Aldrich 99%):  2.5g

1.0 M sulfuric acid: 1.2 L

Sodium bisulfite (NaHSO3, CAS#7631-90-5, Aldrich):   2.0g

0.10 M potassium permanganate (KMnO4): 100 mL

50 mL beakers, 100 mL volumetric flasks, funnels and erlenmeyers

50 mL burets, 10.0 mL and 20.0 mL transfer pipettes

UV-Vis (Spec 20 is fine) and IR spectrophotometers

Implementation Notes: 

Because the synthesis is quick, but the crystals should be allowed to dry, I pair this experiment with another synthesis and analysis experiment, and spend the first lab period on the two syntheses, then the subsequent lab periods on analyses. If you have another experiment that takes 1.5 lab periods, then you can pair appropriately. The 0.5 lab period part is the synthesis. See Instructor Notes for other comments.

Time Required: 
1.5 - 4 hour lab periods (0.5 lab period for synthesis, 1 lab period for analyses)
1 Apr 2013

Online Courses Directory

Submitted by Adam R. Johnson, Harvey Mudd College
Description: 

This website is a free and comprehensive resource that is a collection of open college courses that spans videos, audio lectures, and notes given by professors at a variety of universities. The website is designed to be friendly and designed to be easily accessed on any mobile device.

Course Level: 
Prerequisites: 
Corequisites: 
20 Jul 2012

Soluble Methane Monooxgenase Spectroscopy

Submitted by Gerard Rowe, University of South Carolina Aiken
Evaluation Methods: 

The activities are collected and graded based on how reasonable and well-supported their answers are.

Students also receive a question about inorganic spectroscopy on their final exam.

Evaluation Results: 

Students were generally successful at identifying the right spectroscopic technique for the job.  The most challenging problem was the one concerning spin states, especially because they have to consider all the coupling possibilities for each diiron species and remember what makes a compound EPR active/silent.

 

The final exam question had somewhat more mixed results, probably due to the fact that two weeks had elapsed in between this activity and the exam.

Description: 

Determining the reactive intermediates in metalloenzymes is a very involved task, and requires drawing from many different spectroscopies and physical methods.  The facile activation and oxidation of methane to produce methanol is one of the "holy grails" of inorganic chemistry.  Strategies exist within materials science and organometallic chemistry to activate methane, but using the enzyme methane monooxygenase, nature is able to carry out this difficult reaction at ambient temperatures and pressures (and in water, too!).  This activity asks students to look at the proposed catalytic cycle of soluble methane monooxygenase and choose an appropriate spectroscopic technique to provide different information about the various species in the process.

Learning Goals: 

The student will be able to identify the key features of a scheme describing a catalytic cycle's intermediates

The student will learn to think of spectroscopy as an experiment that operates within a specific time scheme instead of as a figure in a paper

The student will be able to explain the advantages and limitations of different spectroscopic techniques

The student will use their knowledge of spectroscopic techniques to decide the best method to obtain the desired information

Subdiscipline: 
Course Level: 
Corequisites: 
Implementation Notes: 

I give this activity to students towards the end of my advanced inorganic chemistry course.  By this point, they have already been exposed to most of the major spectroscopic techniques used in inorganic chemistry, and have had several lectures in bioinorganic chemistry.  

19 Jul 2012

Electrocatalysis and Proton Reduction

Submitted by Matt Whited, Carleton College
Description: 

These slides provide a brief introduction to the concept of electrocatalysis using the glyoximato cobalt catalysts for hydrogen production recently examined by Peters, Gray, and others.  They provide a suitable introduction to the topic for students interested in reading the primary literature on these topics.

Prerequisites: 
Corequisites: 
Subdiscipline: 
Learning Goals: 
  • A student should be able to define what an electrocatalyst is and the general mechanism by which an electrocatalyst operates.
  • A student should be able to identify a cyclic voltammetric trace corresponding to an operating electrocatalyst and explain why it is different from the electrochemistry of the same complex in the absence of substrate.
  • A student should be able to identify the important features in evaluating the efficiency of an electrocatalyst and define the term "overpotential".
Implementation Notes: 

This set of slides is recommended as background reading (or in-class presentation) for students working on the LO developed from the Valdez et al. PNAS paper "Catalytic hydrogen evolution from a covalently linked dicobaloxime" (the LO is referenced above).

Time Required: 
10-15 minutes
19 Jul 2012

Catalysis: Copper-Mediated Cross Coupling Reactions

Submitted by Sibrina Collins, The Charles H. Wright of Museum of African American History
Evaluation Methods: 

The instructor should provide student feedback based on various areas such as level of preparedness and level of knowledge demonstrated. On problem 4, the goal is for the students to think about possible "criteria" for a mild reaction (i.e. lower temperature, low pressure). They should also recognize steps within the catalytic cycle (e.g. oxidative addition, reduction elimination). Moreover, the students should be able to have a discussion about the importance and significance of these types of cross-coupling reactions.

Evaluation Results: 

TBA

Description: 

This in-class activity introduces students to copper-mediated cross coupling reactions. In the literature, many cross coupling reactions are often discussed using palladium as a catalyst, not copper. In my laboratory, we are synthesizing 7-azaindole-based ligands for the development of potential anti-tumor platinum(II) complexes. In addition, I use one of my own publications to demonstrate an application of this synthetic strategy. The students calculate the actual turnover number (TON) and turnover frequency (TOF) for the copper catalyst.

Learning Goals: 

1) A student will conduct a literature search to gain background knowledge on the Ullmann-type reactions.

2) A student shoud be able to apply their knowledge on Ullmann-type reactions and evaluate the role of each reagent in a given reaction.

3) A student will evaluate the efficiency of a given copper catalyst by calculating TON and TOF.

4) A student should be able to draw a general catalytic cycle for the Ullman-type reaction.

5) A student should be able to identify criteria for a 'mild' reaction.

Equipment needs: 

Chalk board and/or powerpoint

Corequisites: 
Course Level: 
Implementation Notes: 

There are various strategies to implement this activity. After a general overview/lecture focused on the fundamentals of catalysis, the students will complete part 1 listed on the activity.  The students will conduct a literature search on the Ullmann reaction outside of class and complete the questions. During the following class period, we would discuss their answers to the questions for part 1. The second part of the activity focuses on a literature discussion. The students will be required to read the publication by the Collins research group and answer the questions for part 2 of the activity. We would discuss their answers as a group during the following class period.

Time Required: 
50 minutes
19 Jul 2012
Description: 

This is a great web resource for all types of nano materials.  There are lesson plans, demos, activites, labs and lots of background information.  It is very easy to navigate and there are videos of the labs so you can see each step - very useful when doing a type of synthesis or technique new to you.

Prerequisites: 
Corequisites: 
Implementation Notes: 

Students and instructors are able to watch videos and view safety info on a large number of nanomaterials labs and activities.  Truly a variety of skill and equipment levels but very well explained so you know what to expect.

I have used the ferrofluid synthesis proceedure and added some questions and information from the J. Chem. Ed. article listed on the site.  It works very well but pay attention to the notes they include - the iron II chloride needs to be fresh so buy small bottles.

Time Required: 
5 minutes if you know what you want, hours to read it all.
19 Jul 2012
Evaluation Methods: 

Collect responses to questions not covered in class.

Grade class participation.

Assign a more in depth question on an exam. 

Description: 

This learning object was developed at the 2012 NSF sponsored cCWCS VIPEr workshop at UNC-CH where we were fortunate to hear Jillian Dempsey present this research that has appeal to students. This work focuses on an exciting and promising strategy to develop new technology to support a solar energy economy. This literature discussion leads students through a current application in the field of electrocatalysis. The primary literature article for the discussion is found in Proc. Natl. Acad. Sci. USA 2012 109 (39) 15560-15564.

Corequisites: 
Prerequisites: 
Learning Goals: 

Students should be able to:

- identify the chemical reaction presented and balance the half reactions for water splitting

- explain the role of a catalyst in an electrochemical reaction

- propose and evaluate the validity of possible mechanisms based on the experimental data

- find and rationalize trends in the series of catalysts presented in the article

- identify the features associated with electrocatalysis

Subdiscipline: 
Implementation Notes: 

The intent of this literature discussion is geared to provide a broad introduction to the field of electrocatalysis.

Two implementation strategies we thought of are:

  1. Have the students read the article, answer questions 1-4, and watch Chip Nataro’s 5-slides about cyclic voltammetry. In class, discuss questions 5 and 6. For a more in depth discussion, assign questions 7-11.
  2. Have the students read the article and watch Chip Nataro’s 5-slides about cyclic voltammetry the night before. Discuss questions 1-4 in class and assign the questions 5 and 6 for homework.


For a more in depth discussion on electrocatalysis we included a more challenging questions in our document (7-11). These questions could also be used on exams.

Time Required: 
1 class period
17 Jul 2012

Colored Note Cards as a Quick and Cheap Substitute for Clickers

Submitted by Chris Bradley, Mount St. Mary's University
Evaluation Methods: 

Use of the cards gives a rough "eyeball" evaluation of student learning throughout a lecture. Using the cards, for me at least, also provides a gauge of attendance as well and also if it waxes or wanes during the class period.

Description: 

For many years I have resisted using clickers, mainly because at our university there is no standard universal clicker. I wanted to keep student costs as low as possible but also desired the type of live feedback during a lecture that clicker questions can provide. In both my general chem. (200-300 students) and upper division courses (50-75 students), I now pass out 4 or 5 colored notecards on the first day of class and make sure everyone has one of each color. I then do clicker style questions and color code the different answer choices in powerpoint and ask them to hold up their choice after 15-60 seconds depending on the question. This has worked well to provide me instant feedback on difficult topics and doesn't end up singling out any particular student, which most students detest in larger lecture courses.   

 

Learning Goals: 

Students are able to provide feedback to the instructor on questions quickly and "anonymously" and allow one to adjust the direction of a lecture on the fly.   

Prerequisites: 
Corequisites: 
Equipment needs: 

NA

Implementation Notes: 

I typically use between 4-6 clicker questions during a 50 minute lecture. I'm sure someone could use more/less based on an individual's needs. I think the key is to use clicker style questions from the beginning of the class on a daily basis to remind students to bring the note cards in a book/binder/bag. This is really the only problem I have encountered- students often forget their cards. It is probably a wash though, as I'm sure students can also forget clickers.  

Time Required: 
1-5 minutes (depending on the problem)
16 Jul 2012
Evaluation Methods: 

Student learning will be assessed by how well they analyze the last few problems during the in-class discussion. Similar questions will also be included in tests and quizzes.

Description: 

This activity is meant to teach students about the types of homogeneous transition metal C-H bond functionalization catalysts. Before class, the students will read a short discussion of inner- and outer-sphere C-H bond functionalization catalysts. Then they will use their knowledge of transition metal oxidation states and ligands in order to assess whether a variety of catalysts react via inner- or outer-sphere pathways. Based on what they know about these catalysts, they will also decide whether or not the selectivity of these catalysts is mainly dictated by the C-H bond strengths of the substrates.

Learning Goals: 

A student should be able to predict

      - available oxidation states for metals in a variety of complexes.

      - whether a catalyst will undergo one- or two-electron chemistry based on the metal's available oxidation states.

      - ligands that will likely directly react with a C-H bond.

      - whether or not there are any open coordination sites around a metal center.

      - whether a C-H bond functionalization catalyst will react via an inner- or outer-sphere pathway.

      - whether the selectivity of a C-H bond functionalization catalyst will be mainly dictated by the C-H bond strengths

         in the substrates.

 

Corequisites: 
Course Level: 
Equipment needs: 

none

Implementation Notes: 

I have not yet attempted to implement this learning object. It is meant for an organometallic or advanced inorganic class.

Time Required: 
55 - 75 minutes in-class with 15 minutes of before-class reading
9 Mar 2011

Pigment Syntheses and Qualitative Analysis

Submitted by Rebecca M. Jones, George Mason University
Evaluation Methods: 

I assess this group of experiments by pre-lab and discussion questions completed in the lab notebook and overall lab performance.  I also require a formal written report for the white pigment qualitative analysis (Part 2).  This report is in the form of a Journal of the American Chemical Society communication and is graded with a qualitative rubric.  I’ve attached the formal lab report instructions and grading rubric.

 

Evaluation Results: 

The students have enjoyed this set of experiments and showed a good understanding of the precipitation reactions.  As this experiment is near the beginning of the semester, many need to be reminded how to perform a simple stoichiometry calculation to determine percent yield.  The white pigment qualitative analysis experiment is the first of three open ended experiments I feature in this course.  Students have a varying degree of success with the process, but most correctly identify the unknown they were given.  Students have commented that this chemistry is easy to see and has a connection to chemistry in the real world. 

 

Description: 

This set of experiments provides an introduction to simple inorganic synthesis and qualitative analysis of inorganic pigments.  I have taught this series of experiments in my first semester junior level inorganic class for the past 5 years.  In part 1, students synthesize five inorganic pigments.  Part 2 involves identifying an unknown inorganic white pigment by chemical and physical tests.  These experiments are based upon those developed by Dr. Patricia Hill for the Chemistry in Art workshop in 2005 at Millersville University, in Millersville, PA; permission has been obtained from Dr. Hill to disseminate this adapted set of experiments on VIPEr.  The Chemistry in Art workshop is part of the Chemistry Collaborations, Workshops and Communities of Scholars (cCWCS) program.  This experiment was presented at the 20th Biennial Conference on Chemical Education in Bloomington, IN on July 31, 2008; the attached presentation contains images and additional information that may be helpful when implementing this experiment.

Corequisites: 
Prerequisites: 
Learning Goals: 

The students taking this course have completed a year of general chemistry and at least one semester of organic.  As a result, most have adequate knowledge to thouroughly understand the chemistry observed.  At the end of part 1, a student should be able to write and balance the precipitation reactions for synthesis of synthetic malachite, barium white, and chrome yellow.  Students should also be able to qualitatively observe the macroscopic and microscopic syntheses. At the end of part 2, a student should be able to design a qualitative analysis experiment for inorganic pigments and interpret results from these experiments to identify an unknown.

 

Course Level: 
Equipment needs: 

Please see the attached file entitled “Supplies and Implementation Notes for Pigment Syntheses”

 

Implementation Notes: 

Please see the attached file entitled “Supplies and Implementation Notes for Pigment Syntheses”

 

Time Required: 
Each part of the lab handout can be completed in one 3 hour lab period. I schedule 2 weeks for the complete set of experiments.

Pages

Subscribe to RSS - Electron transfer