The dissolved oxygen protocol is the fourth in a series of eight hydrology protocols:

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Grade Levels: Junior High and Up Estimated Time: 15 Minutes for calibration, 15 minutes in the field

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The purpose of the Dissolved Oxygen (DO) protocol is to measure the amount of oxygen dissolved in a water sample. (DO) in water is important for the survival of plants and animals that live in bodies of water. The (DO) protocol involves three parts: calibration and quality control, sample preservation and sample testing. Step 1 - Calibration and Quality Control Before measuring dissolved oxygen, students must calibrate the equipment they will eventually use. Calibration involves checking an instrument before using it in the field. In order to calibrate the 250 ml polyethylene bottle, students must take the temperature of distilled water in the bottle. Step 2 - Sample Preservation The second step of the protocol, sample preservation, involves the addition of a Manganous Sulfate Solution and Alkaline Potassium Iodid Azide, a combination of chemicals that precipitate in the presence of (DO). This means that when the chemical substance is mixed into a water sample a reaction occurs which results in a precipitate, a solid form substance that separates from the water. The addition of this chemical is followed by the addition of Sulfuric Acid, which produces a colored solution in the water. The color will indicate how much of the first chemical solution is present in the water and, therefore, how much (DO) is present in the water as well. Step 3 - Sample Testing The third part of the protocol, the sample testing, involves the addition of a titrant solution. The titrant, Sodium Thiosulfate, will cause a reaction with the precipitate that will cause the color to disappear. The amount of (DO) is calculated from the volume of Sodium Thiosulfate necessary to make the color disappear.

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Dissolved Oxygen Kit Distilled water Squirt bottle 250 ml polyethylene bottle with top Thermometer Latex gloves Safety goggles

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Safety note: The Dissolved Oxygen test kit contains hazardous chemicals. Students must wear the appropriate safety equipment listed in the Dissolved Oxygen test kit including latex gloves and safety goggles. Students must also follow carefully all safety instructions specified by your test kit, including any accompanying Material Safety Data Sheets.

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1) This is an example of a Dissolved Oxygen kit. 2) Students take their water samples from the sampling bucket. 3) Students check for air bubbles in their water samples. 4) Students add the fixative to the water sample and watch the precipitation. 5) Students add the color dye to the water sample with chemical solution. 6) A student holds up the water sample with the chemical components dissolved into the solution. 7) A student fills the titrator with the solution. ? 8) A student carefully drops the titrant solution into the water sample.

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