Lab Report: Dissolved Oxygen
Drew H.
I.
Purpose
The purpose of this test is to see the level of dissolved oxygen in the stream and
use this information to propose a course of action for the future.
II.
Background
Dissolved oxygen is the measure of gaseous oxygen dissolved in an aqueous
solution. For the stream, the dissolved oxygen level needs to be between 5mg/l
and 20mg/l. Dissolved oxygen is used by organic material for decomposition, and
is dictated by the temperature, salinity, and the atmospheric pressure.
Temperature, though, will be the most prominent.
III.
Materials:
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IV.
Thermometer
Pencil
Data Table
Gloves
Manganous Sulfate Solution
Alkaline Potassium Iodide Azide
Sulfuric Acid, 1:1
Sodium Thiosulfate
Starch Indicator
Direct Reading Titrator
Water Sampling Bottle, 60 ml
Procedure
1. Rinse the water-sampling bottle with the sample water.
2. Tightly cap the bottle, and submerge it to the desired depth.
3. Remove the cap and allow the bottle to fill.
4. Tap the sides of the bottle to dislodge any air bubbles.
5. Replace the cap while the bottle is still submerged.
6. Retrieve the bottle and make sure that no air bubbles are trapped inside.
7. Remove cap from the bottle.
8. Immediately add 8 drops of Manganous sulfate solution and 8 drops of
Alkaline Potassium Iodide Azide.
9. Cap the bottle and mix by inverting several times. A precipitate will form.
10. Allow the precipitate to settle below the shoulder of the bottle.
11. Add 8 drops of sulfuric acid, 1:1.
12. Cap and gently invert the bottle to mix the contents until the precipitate
and the reagent have totally dissolved. The solution will be clear yellow to
orange if the sample contains dissolved oxygen.
13. Fill the titration tube to the 20 mL line with the fixed sample. Cap the
tube.
14. Depress the plunger of the titrator.
15. Insert the titrator into the plug in the top of the sodium thiosulfate titrating
solution.
16. Invert the bottle and slowly withdraw the plunger until the large ring on
the plunger is opposite the zero line on the scale.
17. Turn the bottle upright and remove the titrator.
18. Insert the tip of the titrator into the opening of the titration tube cap.
19. Slowly depress the plunger to dispense the titrating solution until the
yellow-brown color changes to a very pale yellow. Gently swirl the tube
during the titration to mi the contents.
20. Carefully remove the titrator and cap. Do not disturb the titrator plunger.
21. Add 8 drops of starch indicator solution. The sample should turn blue.
22. Cap the titration tube. Insert the tip of the titrator into the opening of the
titration tube cap.
23. Continue titrating until the blue color disappears and the solution becomes
colorless.
24. Read the test directly from the scale where the large ring on the titraor
meets the titrator barrel. Record as ppm dissolved oxygen. Each minor
division on the titrator scale equals 0.2 ppm.
V. Data
Testers
Date
Weather
Kit, Drew, Alston
5/5/2011
Cold, sunny
Site
pH
2nd Storm Sewer
1st Storm Sewer
New Circle Runoff
Headwater
Testers
Date
Weather
D.O. (ppm) Conductivity (mpc) Water Temperature (Celsius) Air Temperature (Celsius) Time
6.6
6
650
13.5
18
8.5
12
650
13.5
18
6.9
7
1070
14
18
7.7
10
1070
16
18
1:29
1:52
2:00
2:09
Kit, Drew, Alston
5/9/2011
Hot, sunny
Site
pH
2nd Storm Sewer
1st Storm Sewer
New Circle Runoff
Headwater
Testers
Date
Weather
2:00
8:52
9:55
9:26
Kit, Drew, Alston
5/6/2011
Cold, cloudy
Site
pH
2nd Storm Sewer
1st Storm Sewer
New Circle Runoff
Headwater
Testers
Date
Weather
D.O. (ppm) Conductivity (mpc) Water Temperature (Celsius) Air Temperature (Celsius) Time
7
950
12.5
21.5
8
1010
13
13.5
8
430
12.5
13.5
7
630
18
13.5
7.5
7.2
8.3
6
6.8
8.5
6.9
8.3
D.O. (ppm) Conductivity (mpc) Water Temperature (Celsius) Air Temperature (Celsius) Time
8
670
14.5
25
6.5
740
14.5
25
5.5
1060
13
25
9
1030
15
25
1:26
1:41
1:50
2:00
D.O. (ppm) Conductivity (mpc) Water Temperature (Celsius) Air Temperature (Celsius) Time
8
670
15
26
10
650
15
26
12
1130
16.5
26
7
1040
19
26
1:26
1:42
1:52
2:00
Kit, Drew, Alston
5/10/2011
Hot, sunny
Site
pH
2nd Storm Sewer
1st Storm Sewer
New Circle Runoff
Headwater
7
8.5
7
8.5
VII. Conclusion
Error might have arisen from unintentional sediment in the stream, as there was much
activity before the tests. For higher dissolved oxygen levels in the future, the stream will
need to have more oxidization via riffles, falls, or other features that churn the water.