How to Calculate Dissolved Oxygen in Water
Water typically contains a certain amount of oxygen gas dissolved in it. You can measure the concentration of dissolved oxygen in a sample of water with a procedure known as the Winkler method. This method is commonly performed to estimate the concentration of organisms that a body of water can support. The reagents needed to perform the Winkler test are available in a kit from scientific supply stores.
Things You'll Need
- 300 ml bottle with a stopper
- Water sample
- Calibrated pipette
- 2 ml manganese sulfate
- 2 ml alkali-iodide-azide
- 2 ml concentrated sulfuric acid
- Aluminum foil
- Rubber band
- Beaker
- Sodium thiosulfate
- 2 ml starch solution
Instructions
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1
Fill the bottle to the line with the water sample. Use a pipette to add two milliliters (ml) of manganese sulfate below the water's surface so that you don't add air bubbles to the water. Add two ml of alkali-iodide-azide in the same way.
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2
Place the stopper in the bottle and ensure that there's no air in it. Mix the reagents by turning the bottle upside down several times and wait for the orange solid to settle to the bottom of the bottle.
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3
Pull the stopper out and add two ml of Sulfuric Acid below the surface of the water with the pipette. Put the stopper back in and turn the bottle upside down a few times to dissolve the solid. Place aluminum foil over the stopper and wrap a rubber band tightly around the foil. You may store the sample in a refrigerator for up to eight hours.
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4
Add 201 ml of the prepared solution to a beaker and add sodium thiosulfate one drop at a time while stirring the solution continually. Stop adding sodium thiosulfate as soon as the sample turns pale yellow. Add two ml of the starch solution to turn the sample blue.
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Add sodium thiosulfate one drop at a time while stirring continually until the solution turns clear. The number of milliliters of sodium thiosulfate that you added to the sample will be equal to the milligrams per liter (mg/L) of oxygen that's dissolved in the water.
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