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Acids, pH, and Buffers

Some Basic Chemistry for Biological Science

Terry Platt
Department of Biology
University of Rochester


In this “clicker case,” a three-year-old girl gets into the medicine cabinet and ingests an unknown number of aspirin tablets. Her brother calls 911 and the girl is taken to a nearby hospital, where she is treated. The case is used to discuss the Law of Mass Action, chemical equilibrium and equilibrium constants, pH, and weak acids and buffers in the context of medical management of a life-threatening emergency. It is called a “clicker” case because it is designed to be presented in a class that uses personal response systems, or “clickers.” The case is presented via a series of PowerPoint slides (~400KB) punctuated by multiple-choice questions, which the students answer using their clickers. It could be adapted for use without these technologies. The case is suitable for use in an introductory biology course where integration with biologically relevant chemistry is an important course objective. It could also be used in a chemistry course.


  • Learn that pH numerical correlations with [H+] can often be counterintuitive, but use of the fact that log10 2 = 0.3 allows excellent estimations of pH without using a calculator, and a deeper appreciation of its true characteristics.
  • Understand that carbon dioxide becomes an “acid” when dissolved in water (in-class demonstration).
  • Understands that life can exist only within narrow pH ranges, and the biological control of pH is essential.
  • Learn that the control of pH can be mediated by buffers, usually based on acids with weakly dissociable protons; near their dissociation midpoint, buffers resist pH changes in both directions.


pH; Law of Mass Action; chemical equilibrium; equilibrium constant; acids; bases; buffers; acidosis; aspirin; drug overdose

Educational Level

High school, Undergraduate lower division



Type Methods

Clicker, Interrupted, Demonstration



Subject Headings

Biology (General) Biochemistry

Date Posted


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Callie Pfister
Summit High School
Bend, OR
I occasionally use case studies in my high school classes. I really like this PowerPoint and would use this case in my AP Biology class, but all I see is the PowerPoint, which doesn't contain the story about Molly and her aspirin overdose. Is that only available in the Teaching Notes, or can I get that? It seems like most of the cases on this site are accessible except for explanatory details and the key, even without a subscription. Thanks!


[Editor’s Response: Handouts for students are contained in the teaching notes for this case: Pre-Class Assignment, Pre-Class Handout, and In-Class Handout. The story is included in these handouts.]