To Determine the amount of Dissolved Oxygen (D.O.) in the given sample of water by using Winkler Method

To Determine the amount of Dissolved Oxygen (D.O.) in the given sample of water by using Winkler Method:

Apparatus Required: 300 mm BOD bottle, pipettes, burettes, measuring cylinders, conical flasks

Reagents Required: Standard Manganes Sulphate, Azide Alkali Iodide Reagent, N/40 Sodium Thiosulphate, Starch end point indicator solution, concentrated sulfuric acid etc.

Theory: The amount of oxygen found dissolved in a given water at a given temperature & pressure is the value of Dissolved Oxygen in it. This value increases on increase in pressure & reduces on increase with chloride concentration in water.

Procedure: 

1. Fill the water sample in 300 ml BOD bottle completely.
2. Add 2 ml Manganese Sulphate solution by pipette, dipping the end of it just below the surface of water. So, 2 ml water is spilled out.
3. Add 2 ml Azide Alkali Potassium Iodide similarly.
4. Insert Stopper & mix by shaking the bottle.
5. Red precipitate will form if D.O. is available in water. Allo it to settle halfly and mix it again.
6. Again allow to precipitate half way.
7. Add 2 ml concentrated sulphuric acid to the bottle similarly.
8. Insert Stopper & repeat mixing similarly.
9. Stand the solution fo 5 minutes.
10. Withdraw 101.5 ml of above solution in conical flask.
11. Titrate it with N/40 sodium thiosulphate solution until the yellow colour becomes very light.
12. Add 1 ml starch end point indicator. Blue colour would be developed.
13. Again titrate as earlier till blue colour disappears.
14. Recor final burette reading.

Calculation:

D.O. (in ppm) :  2x

Where x = ml of thiosulpahte used.

Result: The D.O. of the taken water sample is _______ ppm.

Author : Unknown

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