Disadvantages Of Dissolved Oxygen

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3.2.6. Dissolved oxygen
The word dissolved oxygen is used to explain the amount of oxygen dissolved in a unit volume of water. All living organisms are dependent upon oxygen in one form or another to maintain the metabolic processes that produce energy for growth and reproductions. DO is very important parameter for maintain the health of the river, lakes, ponds. Level of the dissolved oxygen is depends on physical, chemical, and biological activity in water body. The minimum DO level is 4 mg/l (ppm) for the survival of aquatic life. Higher value of dissolved oxygen may cause corrosion of steel and iron. Algae growth in water may increase the DO during photosynthesis reaction.
Reagents
• Manganese sulfate solution
• Alkali iodide azide reagent
• Conc. Hydrochloric acid
• Starch indicator solution
• Standard sodium thiosulfate solution (0.025N)
Procedure
• Carefully fill the BOD bottle (300 ml) with a stopper. It should be filled up to the rim and avoid any type of bubbling.
• Add 2 ml of manganese sulfate solution by inserting the calibrated pipette just below the surface of the water and 2ml of alkali iodide azide solution in same manner.
• If oxygen is present brown precipitate is appear.
• After settling the precipitated add 2 ml conc. Sulphuric acid just above the surface. Carefully stopper and invert many times to dissolved the precipitated.
• Measure out 203 ml of solution from the BOD bottle and transfer to a conical flask.
• Titrate with 0.025 N sodium

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