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Dissolved Oxygen R eactions

Dissolved Oxygen R eactions. http:// www.lamotte.com/images/pdfs/instructions/7414.pdf. Dissolved Oxygen Kit Reactions. Step 1:

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Dissolved Oxygen R eactions

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  1. Dissolved Oxygen Reactions http://www.lamotte.com/images/pdfs/instructions/7414.pdf

  2. Dissolved Oxygen Kit Reactions Step 1: Manganous (Manganese II) Sulfate (Manganous Sulfate Solution) reacts with PotassiumHydroxide (Alkaline Potassium Iodide AzideSolution [KOH & KI]) to form Manganous (Manganese II) Hydroxide and Potassium Sulfate. MnSO4+ 2KOH ⎯⎯→ Mn(OH)2 + K2SO4 A precipitate is formed… Mn(OH)2 (s)

  3. Dissolved Oxygen Kit Reactions Step 2: Manganous (Manganese II) Hydroxide reacts with Oxygen &Water to produce Manganic (Manganese III) Hydroxide, (a redox reaction). The ratio of oxygen to Manganese II Hydroxide is 1:4. 4Mn(OH)2 (s) + O2 (aq) + 2H2O (l) ⎯⎯→ 4Mn(OH)3 (s) Product is brown precipitate.

  4. Dissolved Oxygen Kit Reactions Step 3: Manganic (Manganese III) Hydroxide reacts with Sulfuric Acid to produce Manganic (Manganese III) Sulfate and Water. 2Mn(OH)3 (aq)+ 3H2SO4 (aq)⎯⎯→ Mn2(SO4)3 (s)+ 6H2O (l) Oxygen is considered “fixed” at this point.

  5. Dissolved Oxygen Kit Reactions The previous reaction is immediately followed by Manganic (Manganese III) Sulfate reacting with Potassium Iodide (from the step 1 addition of Alkaline Potassium Iodide Azide Solution) to form Manganous (Manganese II) Sulfate and Potassium Sulfate and Iodine. (another redox reaction) Mn2(SO4)3 (s) + 2KI (aq) ⎯⎯→ 2MnSO4 (aq)+ K2SO4 (aq) + I2 (aq) The iodine causes the solution to appear yellow-brown. The amount of iodine is proportional to the amount of oxygen in Step 2.

  6. Dissolved Oxygen Kit Reactions Step 4: Sodium Thiosulfate (S2O3-2) reacts with the Iodine to form Sodium Tetrathionate (S4O6-2) and Sodium Iodide. 2Na2S2O3 (aq)+ I2 (aq)⎯⎯→ Na2S4O6 (aq)+ 2NaI (aq) When all of the iodine has finished reacting, the solution changes color from yellow-brown to colorless. Starch indicator may be added to enhance this endpoint. It will form a blue-black complex with iodine (not iodide ion) when present.

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