To determine Dissolved Oxygen in given Sample by Azide Modification Method

Reactants:

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)

Procedure:

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