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Lab 10 - Experiment 1: Environmental Variables that Effect DO
In this experiment, you will observe environmental conditions that effect the levels of dissolved
oxygen present in a water sample. You will use a LaMotte Dissolved Oxygen TesTabs? to
obtain qualitative data on the levels present in water samples.
(5) 8 ml Test tubes
26 Dissolved Oxygen TesTabs?
1 Canning jar
1 Packet of salt
100 ml Beaker
1 Pair of gloves
Test tube rack
*Printed, color copy of this procedure
*2 Water samples
*You must provide
General Procedure?Analyzing Dissolved Oxygen
Add four LaMotte Dissolved Oxygen TesTabs? to the 8 ml test tube.
Seal with Parafilm? immediately, making sure there are no air bubbles in the sample.
Mix by inverting until the tablets have disintegrated (5-8 minutes).
Wait five minutes.
5. Compare the color of the sample to the color chart below. Record as ppm DO in Table 1.
Effects of Biochemical Oxygen Demand
Field Trip - Water Collection
1. Identify a water location which you believe features abundant micro-organismic, plant or
2. Use graph paper to sketch a diagram of where you will collect your water sample. Be
sure to label the graph with descriptive information, and indicate any other critical
information that might affect the water quality. For example:
? Has it recently flooded?
? Is the area experiencing a drought?
? Is there snow or ice present?
? What is the temperature?
? Is the surrounding animal/marine life steady/predictable?
? What kind of animals/plants are local to the area?
This diagram is called a Field Report and will become useful should you need to reassess the original environment.
3. Label two test tubes with the body of water?s name and the collection date.
4. Go into ?the field? to obtain your water samples. To do this:
? Pack up your test tubes, gloves, aluminum foil, test tube rack, 4 LaMotte
Dissolved Oxygen TesTabs?, a printed copy of this procedure, a timer, and
? Go to the first water sample location.
NOTE: Some collectors may wish to wade into the water to obtain their water
sample. As a general rule of thumb, water collectors should NOT wade into
flowing water if the water depth (in feet) x the water velocity (in feet per second)
is greater than or equal to 10. If you have any hesitations regarding water-safety,
do NOT enter the water!
? Completely submerge one of the test tubes under water.
? Seal immediately with Parafilm?.
? Cover this tube with aluminum foil, and place it in your test tube rack on a flat
surface (if possible). Upon return, this test tube should be stored in a dark
location at room temperature for five days.
? Repeat Step C for the second test tube, and immediately test the DO according
to the procedure listed at the beginning of this experiment (located under the title
?General Procedure - Analyzing Dissolved Oxygen?). Record your data in Table 1.
? Do not return the contents from test tube B to the water as this will contaminate
the water source. Take both of the test tubes back to your ?lab?, place the first
test tube according to Step e, and discard of the second test tubes contents in a
2. After 5 days have passed, repeat the ?General Procedure - Analyzing Dissolved
Oxygen? on the first test tube. Record your data in Table 1
Note: The difference in the DO levels between the uncovered tube (the second test
tube) and the covered tube (the first test tube ) is the biochemical oxygen demand of the
Effects of Temperature
1. Boil water vigorously for 10 minutes.
2. Place a canning jar in the sink and fill with boiling water until overflowing and then cap.
Do not test yet, wait 24 hours.
3. Fill two test tubes with tap water until they are overflowing. Seal immediately with
4. Place one test tube in the refrigerator and leave one at room temperature.
5. Make sure there is no air space between the top of the test tube and the Parafilm?
seal. Let the tubes sit over night.
6. The next day, open the jar from Step 7 immediately and test according to the procedure
above, but use six Test Tab? tablets instead of four.
7. Test the DO levels of the room temperature test tube sample, as well as the refrigerated
test tube sample, with four tablets as normal.
8. After the color change has occurred, take the temperature of each sample and record
the results in Table 1.
Effects of Salinity
1. In a 100 ml beaker, add one packet of salt to 50 ml water.
2. Use this solution to fill a test tube labeled ?brine? until the tube is overflowing. Test the
DO according to the protocol.
Table 1:Dissolved Oxygen (ppm)
Sample after 5 days
Biochemical Oxygen Demand
Effect of Temperature
RT (temperature: ____)
Cold (temperature: ____)
Effect of Salinity
1. Research the Winkler Method for testing dissolved oxygen. Write the protocol for this
testing method and a brief explanation of the reactions that take place within the test.
Also, what are some of the factors that could lead to potential error using this test?
2. State your conclusions on the level of oxygen in the samples you analyzed. What types
of water systems would you expect them to come from? Are these values high or low?
What type of aquatic life would you expect to find in the sources of these samples?
3. Cold, dense water sinks at the poles and drives a deep circulation in the North Atlantic
Ocean. What would you expect the comparative DO levels to be in this water? Why?
4. Biochemical Oxygen Demand (BOD) is the amount of dissolved oxygen required for
aquatic, aerobic biological organisms to break-down organic matter over a period of
time(assuming that temperature and other environmental factors are held at a constant
value). BOD can be used to indicate the organic quality of a given water sample. If a
water sample is undiluted, BOD can be determined with the equation: Initial DO - Final
DO = BOD. If you measure an initial DO of 2.5, and measure a final DO of 1.2 after 5
days have passed, what is the BOD?
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