Purposes: |
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To demonstrate
the concept of parts per million (ppm) and parts per billion (ppb).
To explain how chemicals may be
present in very small amounts in water such that they cannot often be detected by
sight, taste, or smell even though they may still possibly pose a threat to
human health. |
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Background: |
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Concentrations of chemical pollutants in water are frequently
expressed in units of "parts per million" (ppm) which is the same as milligrams per
liter (mg/L). Chemical fertilizers contain nitrate, a chemical that can be dangerous
to infants in quantities as small as 10 parts per million. Trichloroethylene
(TCE), a common industrial solvent, is more dangerous than nitrate and when present
in drinking water in quantities as small as 5 parts per million can cause a higher
than normal incidence of cancer among people who drink the water regularly. |
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Materials: |
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for each group of students: |
1 stirrer (solid coffee stirrers or tooth picks) |
2 containers of clean water (one for diluting and one for rinsing) |
2 dropping pipettes (medicine droppers) |
food coloring (can have different colors for each group) |
set of 10 white plastic spoons, clear containers, or Styrofoam egg carton |
white paper (if clear containers are used) |
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Procedure: |
- If clear containers are used, line them up
side-by-side, place a piece of white paper under each, and number 1 to 10 (left to
right). If egg cartons are used, number each cup.
- Place 10 drops of food coloring into
container #1 (food dye is already diluted 1:10).
- Either place one drop of food coloring
into container #2 or take one drop from #1, transfer it to #2, and rinse dropper.
Transferring the drop of food coloring requires more rinsing but is consistent with
the procedure for the remaining containers. (You may double the drops to obtain
more volume, just be certain that you also double the dilution water in step #4).
- Add 9 drops of clean water to container #2
and stir the solution. Rinse the dropper.
- Use the medicine dropper to transfer 1 drop
of the solution from container #2 into container #3. Add 9 drops of clean water
to container #3 and stir the solution. Rinse the dropper.
- Transfer 1 drop of the solution from container
#3 to container #4. Add 9 drops of clean water to container #4 and stir the
solution. Rinse the dropper.
- Continue the same process until no more color
is visible in the last spoon, container, or egg carton cup.
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Discussion: |
- The food coloring in container #1 is a food
coloring solution which is one part pigment per 10 parts liquid. What is the
concentration for each of the successive dilutions. Use table below (each
dilution decreases by a factor of 10 - 1/10, 1/100, 1/1000, etc.)
- What is the concentration of the solution
when the diluted solution first appeared colorless?
- Do you think there is any of the colored
solution present in the diluted solution even though it is colorless?
Explain. (Yes. The solution is still present but has been broken down
into such small particles that it cannot be seen.)
- What would remain in the containers if all
the water were removed? (Residue from the food coloring, i.e., the
pigment.)
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Extensions: |
- Allow the water in the containers to evaporate
and have students record their observations on what remains in the containers.
- Discuss chemical contamination in drinking
water. Use the list of maximum contaminant levels (MCLs) for some
toxic or carcinogenic chemicals in drinking water (as regulated by the U.S.
Environmental Protection Agency) located at the end of the activity.
These MCLs represent the maximum amount
of a chemical that can occur in drinking water without the water being dangerous
to human health. [Note: Some of the MCLs listed are subject to revision by the
EPA shortly.]
- Explain the relationship between ppm and
ppb and the conversion of these units to milligrams and micrograms per liter.
For example: 1 ppm = 1000 ppb; 1 ppm = 1 mg/L; and 1 ppb = 1 ug/L.
- Try different colored food colorings.
Does the eye perceive color differently? Do some colors "disappear" sooner
than others?
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This activity was adapted from Science Demonstration Projects in Drinking Water (Grades K-12) by the US Environmental Protection
Agency, Office of Water, EPA 570/9-90-007, April 1990.. |
Issued in furtherance of Cooperative Extension
work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, James A. Christenson, Director,
Cooperative Extension, College of Agriculture, The University of
Arizona. The University of Arizona
College of Agriculture is an Equal Opportunity employer, authorized
to provide research, educational information, and other services only
to individuals and institutions that function without regard to sex,
race, religion, color, national origin, age, Viet Nam Era Veteran's
status, or disability.
For problems or questions regarding this web contact Dr.
Kitt Farrell-Poe.
This
document was last modified:
31-Aug-2005
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One part per Trillion ...
Is A Very Finely-Split Hair
Worker exposure to certain chemicals is limited to a few parts
per million. Regulations reduce an industrial waste discharge to one
part per billion. Pesticide residues are found in drinking water in
the low parts per trillion.
Extremely low measurements, and laws and regulations based
on them, are growing more commonplace as science perfects increasing sophisticated
sensors.
Such infinitesimal figures probably don't register with most
people. Only scientists and plant managers trying to get exposures
and effluents down to levels as find as frog hair comprehend and appreciate
their meaning.
Shedding light on the subject, Dr. Warren B. Crumell of the
Down Chemical Company has made some comparisons that put the figures in
perspective (see table below).
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TRACE CONCENTRATION UNITS
UNIT |
1 Part Per Million |
1 Part Per Billion |
1 Part Per Trillion |
Length |
1 inch/16 miles |
1 inch/16,000 miles |
1 inch/16,000,000 miles
(a six-inch leap on a journey to the sun) |
Time |
1 minute/2 years |
1 second/32 years |
1 second/320 centuries |
Money |
1 ¢/$10,000,000 |
1 ¢/$10,000,000,000 |
1 ¢/$10,000,000,000,000 |
Weight |
1 oz salt/31 tons potato chips |
1 pinch salt/10 tons potato chips |
1 pinch salt/10,000 tons potato chips |
Volume |
1 drop vermouth/80 "fifths" gin |
1 drop vermouth/500 barrels gin |
1 drop vermouth/250,000 hogheads gin |
Area |
1 sq ft/23 acres |
1 sq ft/36 sq miles |
1 sq inch/250 sq miles |
Action |
1 bogey/3,500 golf tournaments
1 lob/1,200 tennis matches |
1 bogey/3,500,000 golf tournaments
1 lob/1,200,000 tennis matches |
1 bogey/3,500,000,000 golf tournaments
1 lob/1,200,000,000 tennis matches |
Quantity |
1 bad apple/2,000 barrels |
1 bad apple/2,000,000 barrels |
1 1 bad apple/2,000,000,000 barrels |
Rate |
1 dented fender/10 car lifetimes |
1 dented fender/10,000 car lifetimes |
1 dented fender/10,000,000 car lifetimes |