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## What Is a One Part Per Million Solution?

Author(s): Nancy P. Moreno, PhD, Barbara Z. Tharp, MS, and Judith Dresden, MS.
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#### Let’s Get Started

Have students follow the instructions on the student sheet, "What Does One in a Million Look Like?" Make sure each student group has the following items.

• Six 2-oz cups (numbered 1–6)
• One 9-oz cup of clean tap water
• One empty cup (for cleaning pipettes)
• Two pipettes (one for use with food coloring, one for use with water only)

Students should begin by placing one drop of food coloring into Cup 1. (With younger students, you may elect to place a drop of food coloring into the cup for each group.) Using a clean pipette, students then should add 9 drops of water to Cup 1. Ask, How many drops of food coloring did you add to the cup? and How many drops are in the cup all together? (food coloring and water)

Instruct students to use a pipette to collect one drop of the mixture from Cup 1 and place it in Cup 2. Next, have them add nine drops of water to Cup 2. Be sure they use a clean dropper/pipette for the water. In between steps, students should clean their droppers by rinsing them with tap water and squirting the excess into the empty cup. Each group should repeat this procedure, using one drop from the previous cup and mixing it with nine drops of water until all six cups are filled.

When groups have completed their solutions for all six cups, have them observe the colors of the solution in each cup. Ask, What happened to the color of the water in each cup? In which cup(s) does the color seem to disappear? and  Does this mean that there isn’t any food coloring in the water?

### National Institute of Environmental Health Sciences, NIH

The Environment as a Context for Opportunities in Schools
Grant Numbers: 5R25ES010698, R25ES06932

### Houston Endowment Inc.

Foundations for the Future: Capitalizing on Technology to Promote Equity, Access and Quality in Elementary Science Education