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Chemical Oxygen Demand of Waste water


Materials required


  • Water sample


  • Potassium dichromate solution (0.1N)


  • Sodium sulphate (0.1N)- 15.811g of sodium thiosulphate in 100litres of distilled water.


  • Potassium iodide solution


  • Starch solution (1%)


  • Water bath


  • Titration apparatus


  • 100ml conical flask




1. Water sample is collected from a pond.


2. Poured 10ml of water sample in three 100 ml conical flask labeled as Test1, Test2, and Test3.


3. Simultaneously the distilled water is taken in three 100ml conical flask labeled as Blank1, Blank2 and Blank3. 


4. Added 5ml of potassium dichromate solution in each of the six conical flasks


5. Keep the flask in water bath at 100°C (boiling temperature) for 1 hour


6. Allowed the samples to cool for 10 minutes


7. Added 5ml of potassium iodide in each flasks


8. Added 10ml of sulphuric acid in each flask


9. titrated the contents of each flask with 0.1N Sodium thiosulphate until the blue color disappear completely





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