May 5, 2004

Test for Acidity

How acid is your rain?

MATERIALS

• Litmus paper
• 3 cups
• Juice of 1 lemon
• 1 spoonful of baking soda
• One cup of tap water
• One cup of rainwater

Litmus paper has been treated to change color depending on whether the material being tested is acidic or alkaline (which is the opposite of acidic). It turns blue in the presence of bases (alkali) and red in the presence of acids.

Dip a piece of litmus paper into the tap water. Mix the baking soda with water and dip a piece of litmus paper into this solution. Mix the lemon juice with water and dip another piece of litmus paper into this solution. Observe the difference in the three litmus paper colors. You can also try some common foods to see where they are on the acid-alkaline scale, known as the pH scale (below).

The next time it rains, collect some rainwater in a cup and then dip the litmus paper into the water. Observe the color change and compare it to the three samples you previously tested. Recently, some acid rain has been found to be almost as acidic as lemon juice.

Activity excerpted by permission of Independent Publishers Group from Engineering the City: How Infrastructure Works, Projects and Principles for Beginners by Matthys Levy and Richard Panchyk. Published by Chicago Review Press, distributed by Independent Publishers Group (www.ipgbook.com). Text copyright © 2000 by Matthys Levy and Richard Panchyk.

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