Acid-base chemistry

9 Oct 2019

2019 Nobel Prize - Li-ion battery LOs

Submitted by Barbara Reisner, James Madison University

Congratulations to the 2019 recipients of the Nobel Prize - John B. Goodenough, M. Stan Whittingham and Akira Yoshino. It's a well deserved honor!

There are several LOs on VIPEr that talk about lithium ion batteries and related systems. The 2019 Nobel is a great opportunity to include something about these batteries in your class.

I hope to see more LOs in the coming weeks so we can bring this chemistry into our classrooms!

Prerequisites: 
Corequisites: 
29 Jul 2019

Introduction to Drago's ECW Acid-Base Model

Submitted by Colleen Partigianoni, Ferris State University
Description: 

This LO was created to introduce Drago’s ECW model, which is an important contribution to the discussion of Lewis acid-base interactions. Unlike the qualitative Pearson’s HSAB model (Hard Soft Acid-Base model,) the quantitative ECW model can be used to correlate and predict the enthalpies of adduct formation and to obtain enthalpy changes for displacement or exchange reactions involving many Lewis acids and bases.  Unlike all other acid-base models, graphical displays of the ECW model clearly show that there is no one order of acid or base strengths, and illustrate that two parameters are needed for each acid and base to provide an order of acid or base strength.  The ECW model can also provide a measure of steric strain energy or pi bonding stabilization energy accompanying adduct formation, which is not possible with any other acid-base model. 

This set of slides is intended to provide a basic introduction to the model and several examples of predicting energy changes using the model. It also illustrates how to construct and interpret a graphical display of the model.

 It should be noted that this LO is not in the PowerPoint format, but instead is a more extensive set of notes for instructors who are not familiar with the ECW model. It could be condensed and rewritten in the more standard PowerPoint format.

There is also an ECW problem set LO that can used to supplement this LO.

Prerequisites: 
Corequisites: 
Learning Goals: 

After viewing the slides, students, when provided with appropriate data, should be able to:

  • Calculate sigma bond strength in Lewis acid-base adducts using Drago’s ECW model.
  • Show how to deal with any constant energy contribution (W) to the reaction of a particular acid (or base) that is independent of the base (or acid) when an adduct is formed.
  • Garner information regarding steric effects and pi bond stabilization energy in Lewis acid-base adducts using the ECW model.
  • Show using a graphic display of ECW that two parameters for each acid and each base are needed in acid-base models to determine relative strengths of donors and acceptors.
Evaluation
Evaluation Methods: 

This LO has not been used yet and evaluation information will be posted at a later date.

25 Jul 2019

1FLO: One Figure Learning Objects

Submitted by Chip Nataro, Lafayette College
Corequisites: 
9 Jul 2019

Constructing a Class Acid-Base Titration Curve

Submitted by Katherine Nicole Crowder, University of Mary Washington
Evaluation Methods: 

Students were allowed to keep working until they had correct pH values, so they were graded on participation. Worksheets were collected at the end in order to construct the titration curve.

This could be collected and graded for correctness.

 

Evaluation Results: 

Students were evaluated on similar questions on the subsequent exam. Most students (12 out of 15) scored 11-13 points on a 13 point question where they had to solve for the pH in the four regions of a strong acid titration curve. 8 out of 15 recieved full credit on a question where they had to calculate the pH in the buffer region of a weak acid titration curve.

Description: 

In this in-class activity, each student calculates the inital pH, equivalence volume, and pH at the equivalence point for both a strong acid-strong base and a weak acid-strong base titration.

In addition, each student is assigned a unique volume before the equivalence point and a unique volume after the equivalence point for each titration curve.

The data from the class is then assembled in Excel to construct the two titration curves.

This forces each student to do the calculations for each of the four regions of both types of titration curves. This activity could be used to introduce titration curves or to reinforce previously covered lecture material/problem-solving. It could also be switched to do a strong base-strong acid or a weak base-strong acid titration curve.

The constructed titration curves can be used for further discussions of the differences between a strong acid and a weak acid in terms of initial pH, the rapid-rise portion of the curve, and the pH at the equivalence point.

 

 

Learning Goals: 

A student should be able to

  • determine the pH of a strong acid solution
  • determine the pH of a weak acid solution using Ka
  • use stoichiometry to calculate equivalence volumes for acid-base titrations
  • employ limiting reagent calculations to determine acid or base concentrations for different regions of a titration curve and determine pH
  • determine the pH of a weak base solution using Ka, Kb
Subdiscipline: 
Equipment needs: 

notecards with assigned volumes

computer for entering volume and pH data

Course Level: 
Corequisites: 
Prerequisites: 
Topics Covered: 
Implementation Notes: 

This could be done as an in-class activity (I used a 3 hr lab period - most students took less than 2 hrs) or as a take-home assignment. Students were allowed to use their notes and textbooks. I did not strictly forbid them from working together, but I did tell them that I wanted them to be sure that they could do all of the calculations themselves.

I had an Excel spreadsheet of the correct pH values for each volume (attached). Students were allowed to come check their work with me and continue working if their answers were incorrect. I was also able to help them if they got stuck.

 

Attached are the student worksheets, the class titration curves, and the Excel file I used to calculate the correct pH values. I chose volumes and molarities that would give me an appropriate number of volumes before the equivalence point. Volumes and molarities should be adjusted as needed for the size of your class.

I used whole number volumes, but I think it would be better to have smaller volume increments near the rapid-rise portions of the curves so it doesn't look like the data "jumps" as much.

Time Required: 
1-2 hr
9 Jun 2019

1FLO: PCET and Pourbaix

Submitted by Anne Bentley, Lewis & Clark College
Evaluation Methods: 

I graded each student’s problems as I would any other homework assignment, and they averaged about 80% on that part of the assignment. The other half of the total points for the assignment came from in-class participation.

Evaluation Results: 

We had a rich conversation about this article in class; it was probably one of the most interesting literature discussion conversations I’ve had. Although this was the only introduction to Pourbaix diagrams in the course, 12 of 15 students correctly interpreted a “standard” Pourbaix diagram on a course assessment.

 

Description: 

This set of questions is based on a single figure from Rountree et al. Inorg. Chem. 2019, 58, 6647. In this article (“Decoding Proton-Coupled Electron Transfer with Potential-pKa Diagrams”), Jillian Dempsey’s group from the University of North Carolina examined the mechanism by which a nickel-containing catalyst brings about the reduction of H+ to form H2 in non-aqueous solvent. Figure 3 in the article presents an excellent introduction to the use of Pourbaix diagrams and cyclic voltammetry to determine the mechanism of a proton-coupled electron transfer reaction central to the production of hydrogen by a nickel-containing catalyst.

Corequisites: 
Course Level: 
Learning Goals: 

Students should be able to:

-  identify atoms in a multidentate ligand that can coordinate to a metal as a Lewis base

-  outline the difference between hydride addition to a metal and protonation of a ligand in terms of changes to the overall charge of the complex

-  analyze a Pourbaix diagram to predict the redox potential and pKa of a species

Subdiscipline: 
Implementation Notes: 

I have discussed the challenge of integrating literature discussions into my inorganic course in a BITeS post and the VIPEr forums. Each spring I try something a little different. This year I used three articles from the literature to frame our review of course material at the end of the semester, with each literature discussion occupying a one-hour class meeting.

In each case, the students completed problems before coming to class. While these problems were based on the journal articles, they did not require the students to read / consult the journal articles in order to complete the assignment. The students brought an electronic or paper copy of the article to class. I usually put students in groups (approximately 3 per group) and gave each group new questions to work on, which did draw from the article. After some time working in groups, each group presented their material to the rest of the class.

In implementing this particular literature discussion, I didn’t have any further questions for them.  I walked through some of the other figures from the article (especially Figure 1).  We discussed the authors’ use of color in creating Figure 3. We also reviewed the significance of horizontal vs vertical vs diagonal lines. Because I had not covered Pourbaix diagrams in the course, the activity was a good introduction to the concept.

Because these problems don’t require consultation with the article, they are suitable to use on an exam.

Time Required: 
varies

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