Aquatic Field Investigation
Materials and Methods 5
Measuring pH

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:


Pre-Field Experiment:

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.
  1. Look at the first mystery substance. Does its appearance (color, thickness, etc.) help you determine what it is?
  2. 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?
  3. 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?
  4. Repeat steps 1 through 3 to test the other "mystery substances".
  5. 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.

Field Experiment

  1. To test the pH of the water at your aquatic site, collect a water sample from the bank.
  2. Test the pH of the sample immediately after collecting it. (Changes in temperature can alter the reading.)
  3. Examine the color of the pH paper and match it to the pH scale on your pH kit.
  4. Record the pH value on Master 4a.
  5. 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.
  1. 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?)
  2. What new questions would help you gain more information?
  3. Look for more answers to your questions in the JASON Online Systems, the library, and science textbooks.

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Gene Carl Feldman ( (301) 286-9428
Todd Carlo Viola, JASON Foundation for Education (
Revised: 3 Nov 1995