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Sponges and Bubbles

A Refreshed Investigation of pH and Buffers


Geoffrey M. Lippa
Department of Biology
Alfred University
Heather Zimbler-DeLorenzo
Department of Life and Earth Sciences
Perimeter College at Georgia State University
Jean A. Cardinale
Department of Biology
Alfred University


This directed case study with laboratory components is an adaptation of a “clicker case” by Terry Platt that reviews basic chemistry to explain pH and buffers (see “Acids, pH and Buffers: Some Basic Chemistry for Biological Science” published by the National Center for Case Study Teaching in Science). This adaption shares the same storyline as the original, but also includes two experiments to be completed in class that explore the ways in which the properties of a standard kitchen sponge can be used to understand the important function of buffer systems in the regulation of pH. The case is presented in class using PowerPoint slides and supporting documents, shared either electronically or in print (see Supplemental Materials). The case is ideally suited for an introductory biological or biochemical lecture or laboratory class.


• Define the terms acid, base, and buffer.
• Explain the relationship between acids or bases and the pH of a solution.
• Use the analogy of a common household sponge to describe the action of buffers to bind or release protons, including the physical limitations of a buffering system.
• Describe the equilibrium between carbon dioxide and bicarbonate ions and explain how this equilibrium can be used by the body to regulate blood pH.
• Describe how changes in breathing rate influence blood pH.


Buffer; pH; acid; base, dissociation constant; equilibria; equilibrium; bicarbonate; carbonic acid; pH indicator; acidosis;

Topical Areas


Educational Level

High school, Undergraduate lower division


PDF, PowerPoint, Word

Type / Methods

Directed, Discussion, Laboratory



Subject Headings

Biochemistry  |   Biology (General)  |   Chemistry (General)  |   Medicinal Chemistry  |   Medicine (General)  |   Nursing  |   Pharmacy / Pharmacology  |   Physiology  |   Public Health  |   Science (General)  |  

Date Posted


Teaching Notes

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Teaching notes are intended to help teachers select and adopt a case. They typically include a summary of the case, teaching objectives, information about the intended audience, details about how the case may be taught, and a list of references and resources.

Supplemental Materials

The files below are used to support this case study (see Teaching Notes for details).

  Reading Guide (PDF)
  Pre-Class Reading (PDF)
  In-Class Reading (PDF)
  Experiments Worksheet (MS Word)
  Mini-Essay Assessment Grading Rubric (MS Word)

Answer Key

Answer keys for the cases in our collection are password-protected and access to them is limited to paid subscribed instructors. To become a paid subscriber, begin the process by registering.