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Find Dissolved Oxygen in given Sample by Azide Modification



  1. MnSO4

  2. Alkali

  3. Iodide Azide (NaoH + NaH3 + NaI)

  4. H2SO4 conc.

  5. Starch Indicaoter,

  6. Na2S203(N=0.025)

  7. Oxygen is required for all living organisms 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 NaSO3 to another sample (oxygen become zero)

  3. Add MnSO4 add alkali iodide axide color while means no oxygen.

  4. Add 2ml H2SO4 ro disolve (in first sample) color becomes as mastard oil

  5. Remove 100ml from the sample

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

  7. Take NaS2o3 in burrette

  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 Na2SO3 = 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 +2H2o


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