Developed by:  Catherine R. Ney
Subject:  Physical Science
Unit:  Environmental Pollution
Grades:  Middle grades: 4-8

Acid Test

Objective:
 1.  To determine the pH of water using a litmus test.
 2.  To rank order common substances according to pH.
 3.  To infer a healthy environment has a neutral pH.

Material:
 litmus paper (purchased from Carolina Biological) common substances:  vinegar, ammonia, tap water, rain water, cola soft drink, lemon juice, bleach, ... beakers or clear containers for common substances tested

Procedure:
 1. Students rank order substances from acidic to basic (0 is extremely acidic, 14 is extremely basic, and 7 is neutral) using the litmus paper test.
 2. Students place one litmus paper in each common substance.  Next, they label each litmus paper with the name of the substance tested. Then each labelled litmus paper is placed on a bar graph from red (acidic) to blue (basic).  Students discuss that tap water (neutral is healthy.  Display results on a class bulletin board.
 3. Option:  Students can place pennies in each substance.  Discuss how acidity affects each?

Discussion:
 1. Discuss how acid rain affects them and their community.
 2. View the PBS 27-minute film, "Acid Rain-Requiem or Recovery."  Discuss acid rain's impact.
 3. Examine and discuss the costs of controlling acid rain vs. the costs of leaving it unchecked.

Evaluation:
 1. Assess students participation in testing the pH of common substances with litmus paper.
 2. Evaluate students contributions to the acid rain discussion.
 3. Review and test students' understanding of the bar graph on acidity.