At this station your team will measure whether water at the aquatic site is
acidic or basic (alkaline) and learn what that indicates about the water. The
most common way to determine whether water is acidic or basic is to
measure the concentration of hydrogen ions in the water-by testing the
water's pH. (The term "pH" comes from combining the letter "p" from the
German word potenz, meaning "power," with H, the chemical symbol for
hydrogen.) Changes in pH values of water are important to the health of
many organisms. Most aquatic organisms have adapted to life in water with a
specific pH; if the pH changes, the organisms may die.
For the Pre-Field station:
For the field station:
- pH kits
- Samples of "mystery substances"
- pH kits
- Baby-food jar, clean
- Your team's copy of Master 4a, "Baseline Study and Possible Human Impact
Examine the pH scale on your pH kit. The pH scale ranges from 0 to 14. A pH
measurement of 7 indicates that the water is neutral-neither acidic nor basic.
As pH values increase from 7, so does the alkalinity of the substance. Thus, a
substance with a pH of 14 is a very strong base (very alkaline). As pH values
decrease from 7, acidity increases. Thus, a substance with a pH of 1 is a very
strong acid. It is also important to note that each increment on the pH scale
represents a tenfold change. That is, water with a pH of 9 is ten times more
alkaline (basic) than water with a pH of 8.
- Look at the first mystery substance. Does its appearance (color, thickness,
etc.) help you determine what it is?
- Open the jar. Then, holding the jar away from your face, wave your hand
over the top of the jar toward your nose a few times. DO NOT
STICK YOUR NOSE OVER THE JAR AND SNIFF DIRECTLY! Does the
odor help you determine what it is?
- Take a strip of pH paper and dip it in the substance. Remove it and watch
for a change in color. Match the color to the pH scale on your pH kit. What
is the pH? In your JASON Journal, record the code letter that your teacher
has written on the container. Next to the letter, record the pH for that
substance. Is the substance acidic or basic? Does this information help you
identify the substance?
- Repeat steps 1 through 3 to test the other "mystery substances".
- Once you have recorded the pHs of all the substances and guessed what
they might be, your teacher will tell you what each substance is. Write this
information next to the pH readings in your Journal.
- To test the pH of the water at your aquatic site, collect a water sample from
- Test the pH of the sample immediately after collecting it. (Changes in
temperature can alter the reading.)
- Examine the color of the pH paper and match it to the pH scale on your pH
- Record the pH value on Master 4a.
- Examine the diagram showing pH ranges that can support life. Why do you
think that the pH range of 6.5 to 7.5 supports the most life?
After you have completed both the Pre-Field and Field Experiments, discuss
the following questions within your research team and record your answers
in your JASON Journal.
- What is the pH of your rainwater? What was the pH of the water at your
aquatic site? What do your measurements indicate about the water at your
aquatic site? (Hint: What could make the pH of the rainwater differ from
the pH of the water at your aquatic site?)
- What new questions would help you gain more information?
- Look for more answers to your questions in the JASON Online Systems,
the library, and science textbooks.
Return to the Aquatic Field Investigation
JASON VII Home Page
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Gene Carl Feldman
Todd Carlo Viola, JASON Foundation for Education (firstname.lastname@example.org)
Revised: 3 Nov 1995