Summer Research Program for Science Teachers
Paul Melkonian
1999
Water Quality Monitoring
Dissolved Oxygen
Goals: The goal is to have students come up with consistent water quality data for a region over a semester and to analyze the data. [Teaching Standard D- Structure time for extended investigations]
Objectives:
1: Quantify the amount of Dissolved Oxygen in a body of water. [Content Standard Unifying Concepts- Change, constancy, and measurement]
2: Use data collected to measure the water quality index for a body of water.
3: Become proficient with a procedure that will be used throughout the term.
Do Now: On
a piece of paper, describe what would happen to the class if we
slowly decreased the amount of oxygen in the room. Then what
would happen if we slowly increased the amount of oxygen in the
room. Share a few responses with class.
(5-10 minutes)
Starting questions:
1. How does this example relate to dissolved oxygen?
2. Why is measuring DO important?
3. Why is measuring water quality important? [9-12 Content Standard F- Environmental quality]
4. What are other factors that go into measuring water quality? [9-12 Content Standard A- Identify questions/concepts that guide inquiry]
(5-10 minutes)
Lab Materials:
Bottle with stopper
DO reagent pillow#1 (manganous sulfate powder)
DO reagent pillow#2 (alkaline iodine azide powder)
sodium thiosulfate (PAO titrate)
DO pillow #3 (sulfamic acid powder)
starch solution
square mixing bottle
dropper
graduated cylinder (100mL)
clippers
barometer (pressure measurement) [Teaching Standard D- Make accessible science materials]
Lab Procedure:
1. If you have a barometer, record the atmospheric pressure. Remove the stopper and immerse the DO bottle beneath the river's surface. Use gloves to avoid contact with water.
2. Allow the water to overflow for 2 or 3 minutes. (This will ensure the elimination of air bubbles.)
3. Make sure no air bubbles are present when you take the bottle from the water.
4. Add the contents of pillow #1 and pillow #2 to the DO bottle.
5. Insert the stopper, making sure no air is trapped inside, and shake vigorously to fully mix. Be careful not to splash the chemical-laden water. Wash your hands if you contact this water. If oxygen is present in the sample, a brownish orange precipitate will form. If air bubbles form after the first shake, discard the sample and begin again.
6. Allow the sample to stand until the precipitate settles halfway. When the top half of the sample turns clear, shake again, and wait for the same changes.
7. Add pillow #3 to sample, and shake. The precipitate will dissolve and the water will turn yellow.
8. Pour sample to top of the graduated cylinder; pour the contents of the graduated cylinder into the square mixing bottle, do this again.
9. Add one or two drops of starch solution to turn the solution blue.
10. Add 1 drop of titrate (PAO) to the square mixing bottle and swirl. Be careful to hold the dropper straight up and down above the bottle. While swirling the sample to mix, continue adding PAO titrant to the prepared sample one drop at a time. Count the number of drops needed to change the sample from blue to a clear solution. [9-12 Content Standard B- Chemical reactions]Hold the bottle against white paper to see the color change accurately. Each drop equals 0.5mg/l of dissolved oxygen.
11. Calculate the DO.
Add to water quality index chart. (which
includes……)
1. Dissolved Oxygen
2. Fecal Coliform
3. pH
4. BOD
5. Temperature
6. Total Phosphate
7. Nitrates
8. Turbidity
9. Total Solids