Helpppp (1 Viewer)
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In case you don't know, it is not compulsory to know the complicated Winkler method.
Instead, you can refer to the electrolysis method in which an 'electrolytic oxygen sensor' is used to determine Dissolved Oxygen. The sensor is placed above the test solution and oxygen diffuses into it.
This causes reduction at the cathode in the sensor: (O2)+(4H+)+(4e-)=(2H2O)
and oxidation at anode: (Ag)+(Cl-)=(AgCl)+(e-) as there is buffered HCl in the sensor.
The conentration of oxygen is proportional to the electric current produced in the sensor.
Instead, you can refer to the electrolysis method in which an 'electrolytic oxygen sensor' is used to determine Dissolved Oxygen. The sensor is placed above the test solution and oxygen diffuses into it.
This causes reduction at the cathode in the sensor: (O2)+(4H+)+(4e-)=(2H2O)
and oxidation at anode: (Ag)+(Cl-)=(AgCl)+(e-) as there is buffered HCl in the sensor.
The conentration of oxygen is proportional to the electric current produced in the sensor.
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The Winkler method involves the reaction of sodium thiosulfate and oxygen gas with manganese and iodide ions as intermediate reactants.
o Step 1: Oxygen oxidises Mn2+ (2Mn2+ + O2 + 4OH- → 2MnO(OH)2).
o Step 2: The resulting solution is then acidified and iodide ions are added (MnO(OH)2 + 2I- + 4H+ → I2 + Mn2+ + 3H2O) (Iodide is oxidized to iodine).
o Step 3: The iodine is then titrated with sodium thiosulfate solution (I2 + 2S2O32- → 2I- + S4O62-).
Starch is used as an indicator as it forms a deep blue colour with iodine. The formation of a colourless solution
o Step 1: Oxygen oxidises Mn2+ (2Mn2+ + O2 + 4OH- → 2MnO(OH)2).
o Step 2: The resulting solution is then acidified and iodide ions are added (MnO(OH)2 + 2I- + 4H+ → I2 + Mn2+ + 3H2O) (Iodide is oxidized to iodine).
o Step 3: The iodine is then titrated with sodium thiosulfate solution (I2 + 2S2O32- → 2I- + S4O62-).
Starch is used as an indicator as it forms a deep blue colour with iodine. The formation of a colourless solution