K I D · C O N N E C T I O N

Parts Per . . .

Inves T. Gator was happy to read in the paper that his drinking water was considered to be very safe and clean, yet the article said the water contained lppm (one part per million) of fluoride,

10ppm (ten parts per million) of sulphates, and 100ppm (one hundred parts per million) of chloride. Inves T. Gator was puzzled! He looked at a glass of water he was about to drink, and he didn't see anything in it. It looked clean and tasted great, but it was supposed to contain all of these minerals. "How much is a part per million?" he wondered? This sounds like a mystery for Inves T. Gator to solve! Help Inves T. Gator seek an answer to this puzzle by determining what "parts per million" and "parts per thousand" are. Use the materials listed below and follow the directions given under the heading "Procedure" below.

Materials:
 
White ice cube tray or Styrofoam egg carton.

1 stirrer (coffee stirrers or popsicle sticks are great!)

1 medicine dropper

Food coloring (blue or red works best)

Permanent marker

Source of water

Procedure:
This experiment illustrates the concept of "parts per," such as "parts per thousand" or "parts per million."

NOTE:

Food coloring is usually packaged as a 10 percent solution or a 1/10 dilution (1 in 10 dilution). As nine drops of water are added to one drop of this "one drop per 10" solution, this forms a 1/100 dilution of "one part per 100" solution (well #2). One drop of this in well #3 with nine drops of water makes a 1/1,000 dilution or "one part per 1,000" solution and so on until a "one part per million" is produced in well #6.

Special thanks to:

CEPUP - Chemical Education for Public Understanding Program
Lawrence Hall of Science
University of California
at Berkeley
Addison Wesley
Publishing
  1. Using the permanent marker, number the ice tray or carton wells with the numbers 1-8.
  2. Fill ice cube or carton well #8 with water. This will be used to rinse the medicine dropper after each use.
  3. Place 10 drops of food coloring in well #1.
  4. Remove one drop of food coloring from well #1 with the dropper and add it to well #2. Rinse the dropper by alternately removing and adding water in the rinsing well (#8). Be sure to fill the dropper and discard the water after each drop of coloring is added. If the water used to rinse the dropper is not discarded, cross contamination will occur. Now add 9 drops of clean water to #2 and mix with stirrer.
  5. Add one drop of solution from well #2 to well #3 with the dropper. Rinse the dropper in well #8 using the instruction in D. Next add 9 drops of clean water to well #3 and mix.
  6. Repeat steps D-E for wells 4-6.
  7. Did you place food coloring in all of the wells? How do you know?
  8. Look at the solutions in the wells. In which wells can you see the color? In which wells do you not see the color?
  9. Do you think there is food coloring in the wells that do not appear to be colored?
  10. Would you drink a glass of water containing the amount of food coloring that is in well #6? Well #5? Well #4? Well #2? Why or why not?
  11. Would you drink water that contained lppm of arsenic; of sodium?

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