Acids, pH, and Buffers

By Terry Platt

Abstract

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.

Download Case

Date Posted

05/28/2010

Overview

Objectives

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.

Keywords

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

Subject Headings

Biochemistry

Biology (General)

EDUCATIONAL LEVEL

High school, Undergraduate lower division

FORMAT

PDF, PPT

TOPICAL AREAS

N/A

LANGUAGE

English

TYPE/METHODS

Clicker, Interrupted, Demonstration

Teaching Notes & Answer Key

Teaching Notes

Case teaching notes are protected and access to them is limited to paid subscribed instructors. To become a paid subscriber, purchase a subscription here.

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.

Download Notes

Answer Key

Answer Keys are protected and access to them is limited to paid subscribed instructors. To become a paid subscriber, purchase a subscription here.

Download Answer Key