Activity
Many people find
water regulations and drinking water quality reports difficult
to understand. Ask the students, “Have
you ever heard about the “Maximum Contaminant Level” of
a toxic in the water? What do you think it means?” (The
MCL defines the maximum amount of contaminant that can be
present in drinking water for the water to be considered
safe.) Allow for guesses and discussion.
Tell
the students, “Most often, the MCL is described
as “X parts per million” or “Y parts per
billion. For example, the MCL for Arsenic is  or
 , according to the web site (In 2006 this MCL will change
to 0.01ppm
or 10ppb). http://www.dhs.ca.gov/ps/ddwem/chemicals/MCL/EPAandDHS.pdf
What does this
mean? How small is one part per million? Allow time for examples
and discussion. Tell the students, “Today
we are going to do some activities that will give you a better
picture of the size of one ppm and one ppb”.
Separate the class into groups and assign each of the groups
one of the following activities.
I) Measuring
the Room: Students find out how many cubic
centimeter blocks are needed in the classroom to represent
one part per million
The following activity is adapted from the activity described
at the web site
http://www.so.wustl.edu/science_outreach/curriculum/ozone/activities/1F-Measuring.pdf.
1. Have the students in the group use meter sticks to find
the length, width, and height of the room in centimeters,
to the nearest whole centimeter
2. Calculate the volume of the room in cubic centimeters
by multiplying these dimensions together.
3. To calculate how many cubic centimeter blocks are needed
in the classroom to represent five parts per million in the
classroom, use the formula:
4. Have the students construct the appropriate number of
cubic centimeter blocks to show the class what a concentration
of 5 parts per million looks like.
5. Ask the group how they would represent 5 parts per billion.
II)
How many sheets of paper: Students determine
how many sheets of  paper
are needed to have one million  if
1 represents
the number 1.
The following activity is adapted from the activity described
at the web site
http://www.learner.org/jnorth/tm/PPM.html
You will need a sheet of 8 1/2 x 11-inch computer paper and
a pen or pencil.
1. Calculate how many square centimeters are in the sheet
of paper
2. Mark off one square centimeter. Based on your calculation
above, how many square centimeters would fit on one sheet
of paper?
3. How many sheets of paper would you need to make your
little square centimeter be one part per million?
4. A
ream of paper is 500 sheets. How many reams would you need
to represent 1,000,000 .5. How
sheets of paper would you need to make one represent
a concentration of one part per billion?
6. How many reams of paper would you need to represent a
concentration of one part per billion?
III) How big is one drop? Students first determine the number
of drops of water in one milliliter and use that number
to determine how many gallons of water would equal 1 million
drops?
The following activity is adapted from the activity described
at the web site
http://www.learner.org/jnorth/tm/PPM.html
1. Take an eyedropper that is marked in milliliters and fill
it with exactly 2 milliliters of water. Now squeeze the bulb
slowly, drop by drop, counting exactly how many drops come
out as you bring the level to 1 milliliter. How many did
you count? Do 10 different trials of this.
2. Do you all get the same answer each time? If not, how
far apart are the numbers? What might account for the differences?
Calculate the average number of drops per milliliter.
3. Using the average number of drops per milliliter, calculate
the number of milliliters would equal one million drops.
4. Convert  into 
5. That means one part per million is the same as one drop
of a substance in a million drops, or Y liters, of water.
6. There
are 3.78 liters in a gallon. Use this fact to calculate
how many gallons are in Y liters. This will tell you that
one part per million is also the same as one drop of a substance
in about  gallons.
7. If a bathtub holds about 60 gallons of water, how many
drops of food coloring would be needed to bring a full bathtub
to the concentration of one ppm?
8. How many gallons of water would you need if one drop of
water were to represent a concentration of one part per billion?
IV) Dilution: Students will understand that a mixing ratio
is the concentration of a certain substance expressed in
parts per million or parts per billion by volume.
The following activity is the activity described at the
web site
http://www.ucar.edu/learn/1_5_2_24t.htm
1. Using masking tape and markers, label the test tubes 1 through
10.
2. Put 9 ml of water in test tubes 2 through 10.
3. Put
10 ml colored liquid in test tube 1.
4. Take an eyedropper that is marked in milliliters and
draw 1 ml of the colored liquid from test tube 1 into the
eyedropper and transfer it to test tube 2.
5. Shake test tube 2 to mix the colored liquid and the water.
6. Draw 1 ml of the liquid in test tube 2 into the eyedropper
and transfer it to test tube 3.
7. Shake
test tube 3 to mix the colored liquid and the water.
8. Continue this process with the rest of the test tubes,
4-10. The concentration in each test tube is getting lower
by a factor of ten each time.
9. Next
fill out the mixing ratio in the chart provided. Test tube
1 contains pure color, so its mixing ratio is one
part in one = 1/1 = 1. Write this down for the mixing ratio
in the parts by volume column.
10. Test
tube 2 has one part coloring for ten parts liquid. What
is the mixing ratio? (1/10) Write this number in your
chart and translate it into exponential notation ( ).
11. Continue
this process for the other test tubes.
12. Now
convert into parts per million by volume by multiplying
the parts by volume (the second column). This will tell you
how many parts per million by volume you have in each test
tube.
Container number
|
Parts by volume
(mixing ratio)
|
Parts per million by
Volume (ppmv)
|
Parts per billion by
Volume (ppbv)
|
1
|
1/1 = 1 |
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2
|
1/10 =  |
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3 |
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4 |
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5 |
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6 |
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7 |
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8 |
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9 |
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10 |
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13. Convert the ppm into ppb by multiplying the number in
column three by 1,000 (since one billion is 1000 times as
large a one million)
Homework
1. If the students have not completed the calculations involved
in their activities, have them do so for the first part of
the homework. Tell them that they will present to the class
tomorrow.
2. Have students come up with representations for one part
per million given the following units to represent one unit:
a. one inch in how many miles? (5280 feet = 1 mile)
b. one cup in how many gallons? (16 cups = 1 gallon)
c. one pound compared to the weight of how many female adult blue whales?
(maximum weight of female blue whale  according
to http://www.acsonline.org/factpack/bluewhl.htm)
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