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To determine Dissolved Oxygen in given Sample by Azide Modification Method



  1. MnSo4

  2. Alkali

  3. Iodide Azide (NaoH + NaH3 + NaI)

  4. H2S04 conc.

  5. Starch Indicaoter,

  6. Na2S203(N=0.025)

  7. Oxygen is required for all living organisums for growth (metabolism) 21% in air quantity directly related with atm pressure and inversly proportional to temp for trout 7.5 mgl required

  8. BOD (vol= 300 ml)


  1. Add 2ml alkali iodide azide if becomes yellow = oxygen present while no oxygen ppt will be created let it settle ( Na2S03, Sodium sulphride) brings oxygen to zero

  2. Add NaS03 to another sample (oxygen become zero)

  3. Add MnSo4 add alkali iodide axide color while means no oxygen.

  4. Add 2ml H2S04 ro disolve (in first sample) color becomes as mastard oil

  5. Remove 100ml from the sample

  6. Add 1ml startch indicator to the remaining sample => color = blueish

  7. Take NaS2o3 in burrete

  8. Titrate the sample against it until it becomes colorless ==> initial reading=4ml ==> final reading=12.6ml ==> 12.6-4=8.6ml

  9. ++ (oH) 1ml of Na2S03 = 1mgk of dissolved oxygen it contains 8-6 mgk of dissolved oxygen Mn + H2O => M(oH)2

  10. Mn (oH)2 + 1/2 o2 =>Mno2+ H2O

  11. Mno2 + 2i + 4H + => Mn + i2 +2 H2O

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