Submitted by Mona Kulp / Smith College on Wed, 01/27/2021 - 15:34
My Notes
Categories
Prerequisites
Corequisites
Course Level
Topics Covered
Description

This is a virtual adaptation of a buffer capacity lab experiment using the chemcollective digital workspace.  Students learn to make buffers in different ways and then test the capacity of their buffers to understand what makes an optimal buffer.

Attachment Size
Buffer solutions virtual lab handout 32.11 KB
Learning Goals

Goals

  1. To examine the behavior of buffer solutions.
  2. Learn to prepare buffers in different ways.
  3. Test the capacity of the different buffers.
Equipment needs

A laptop or chromebook to access the chemcollective website.

Implementation Notes

This is a virtual lab experiment that will be conducted synchronously on zoom. Students will be partnered up in zoom breakout rooms to use the digital lab space and collect the pH data on all the buffer solutions that they “prepare”.

Time Required
One 3 hour lab session
Evaluation
Evaluation Methods

Students write a partial lab report (introduction and results and discussion sections only) that is graded for this exercise.

Evaluation Results

Students are usually surprised that buffers A, B,C and E have the same initial pH when they are prepared in different ways. They have to rationalize this observation using the Henderson-Hasselbach equation. They have to also explain why buffer D has a different initial pH. 

Buffers A, D and E are made using the weak acid and conjugate base but buffers B and C are made with either weak acid and strong base or conjugate base and strong acid. Students are sometimes confused by this method of making a buffer and don’t always see the difference between this and the second part of the experiment which involves using the strong acid or base to test the capacity of the buffer.

The second part of the experiment is to understand the buffer capacity of the five buffers and to explain why only one buffer (E) is still acting as a buffer after the addition of strong acid and base. Students are also asked to calculate the pH of buffers A and E before and after the addition of the strong acid and have to realize that they can no longer use Henderson-Hasselbach to calculate the pH of buffer A after the addition of HCl, because it is no longer a buffer. 

 

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