8 Apr 2020

Electrochemistry: Galvanic Cells and the Nernst Equation

Lab Experiment

Submitted by William Polik, Hope College
Categories
Corequisites: 
Prerequisites: 
Course Level: 
Description: 

In this online Electrochemistry Experiment, students use an Electrochemical Cell Simulator to construct electrochemical cells, measure voltages, and interpret results.

 
Learning Goals: 
  1. Students will write balanced redox (reduction and oxidation) reactions.

  2. Students will calculate cell voltages under standard solution concentration conditions for a galvanic cell.

  3. Students will use the Nernst Equation to calculate electrochemical cell voltages under non-standard solution concentration conditions for a galvanic cell.

  4. Students will use the Nernst Equation to create a graph for a concentration cell and use the slope and intercept to find the concentration of an unknown (given its cell potential).

Equipment needs: 

This experiment relies upon the Electrochemical Cells simulator available at

http://web.mst.edu/~gbert/Electro/Electrochem.html

written by Dr. Gary L. Bertrand at the University of Missouri-Rolla.

 
Implementation Notes: 

This lab was developed during the COVID-19 crisis to replace our normal in-person general chemistry lab. All resources were shared with students in the course management system. 

Students watch two videos, one about electrochemistry concepts (our students had not seen electrochemistry in lecture yet) and the other about the operation of the simulator. [Note: Videos are posted as "Faculty-only Files."]

Students make a copy of the Electrochemistry Lab Template (as a Google Doc), which guides them through the experiment. (Note: We put a link to the Google Doc of the Template in our course management system. It was set up so that when they clicked on the link, it automatically made a copy of the Google Doc for them.) Following the instructions in the Template, they run experiments on the Simulator and record their results in the Template. They also do some calculations in the Template.

When they have completed the tasks outlined in the Template, they export the document as a pdf and upload the pdf file to the course management system.

Laboratory materials were posted to all general chemistry laboratory sections on a Monday morning. Students met briefly (synchronously) with their laboratory sections during the first week to clarify expectations. During the second week, there were optional lab meetings so that students could get any questions answered. The completed laboratory template was due Friday of the second week.

Time Required: 
One-two weeks *see note in implementation on timing
Evaluation
Evaluation Methods: 

The completed worksheets were graded on a 50 point scale with 10 points/question.

Evaluation Results: 

Results for one lab section:

Average score was 40.8/50 points

Students frequently neglected to put units on their results. Up to three points were taken off for this (one for the first instance, one for the slope of their Nernst equation, and one for the molarity of their unknown).

Most students were not able to calculate the concentration of their unknown solution (4D). Some were able to find Q, but did not realize that they needed to substitute "1 M" for "Right Conc" and then solve for "Left Conc." (-2)

At least two students swapped their slope and intercept in the unknown concentration calculation (4D). (-2)

Many students did not include an electrochemical reaction in the final "application" question, but most included a citation! (-2)

Most of these problems can be addressed in the next iteration of the instruction.

Creative Commons License: 
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