Apparatus Chemicals Required
A. Manganous sulfate solution for 1000 mL
Dissolve one of the following in 1000 mL of distilled water
480 g MnSO4.4H2O or-
400 g MnSO4.2H2O or-
364 g MnSO4.H2O
B. Alkali-iodide (add azide if necessary) for 1000 mL
Dissolve in 1000 mL of distilled water
500 g NaOH or- -AND- 135 g NaI or-
700 g KOH 150 g KI
Use azide while taking bacterial or nitrite laden samples
Dissolve 10 g NaN3 in 40 ml distilled water.
Add to 1 L of above solution.
C. Sulfuric acid (concentrated)
D. Starch for 100 mL
Dissolve 2 g soluble potato starch in 100 ml hot distilled water, stir.
(NOTE Add starch only to hot water as starch may take a little time to liquefy.)
E. Sodium thiosulfate for 1000 mL
In 1000 mL distilled water add 6.25 g Na2S2O3.5H2O
(NOTE As the solution is unpreserved, so must be freshly prepared.)
Materials
We require Test tubes with known volume or standard Biological Oxygen Demand water sampling bottles, few Beral Pipets, use Burets or preferably 10 mL syringes and Erlenmeyer Flasks
Methodology
In this Winkler Titration method, manganous sulfate was made to react with a potassium hydroxide-potassium iodide compound mixture to give out a white flocculent precipitate of bivalent manganese i.e. manganous hydroxide
MnSO4 2 KOH Mn(OH)2 K2SO4
This precipitate was then made to react with dissolved oxygen in water to get tetravalent manganese
2 Mn(OH)2 O2 2 MnO(OH)2
Product formed, manganic basic oxide, is a brownish precipitate. Whereas if, a white precipitate comes out it indicates that no oxygen is present. Further, with acidification through sulfuric acid (or sulfamic acid, H3NSO3) the precipitate gets dissolved, forming out manganic sulfate
MnO(OH)2 2 H2SO4 Mn(SO4) 3 H2O
Formed manganic sulfate was made to react with potassium iodide yielding free iodine (I2), which gives out a brownish color. Iodine on the other side also tends to react with starch and bring into being a blue-black color which indicates the presence of iodine. This iodine can be titrated with sodium thiosulfate to give out sodium iodide, which will no further leave the brown color
2 Na2S2O3 I2 Na2S4O6 2 NaI
As a result we measured the amount of thiosulfate needed to eliminate all of the brown color, and helping in determination for total amount of I2 in the sample, and in a roundabout way giving us the amount of O2 present dissolved in
Dissolve one of the following in 1000 mL of distilled water
480 g MnSO4.4H2O or-
400 g MnSO4.2H2O or-
364 g MnSO4.H2O
B. Alkali-iodide (add azide if necessary) for 1000 mL
Dissolve in 1000 mL of distilled water
500 g NaOH or- -AND- 135 g NaI or-
700 g KOH 150 g KI
Use azide while taking bacterial or nitrite laden samples
Dissolve 10 g NaN3 in 40 ml distilled water.
Add to 1 L of above solution.
C. Sulfuric acid (concentrated)
D. Starch for 100 mL
Dissolve 2 g soluble potato starch in 100 ml hot distilled water, stir.
(NOTE Add starch only to hot water as starch may take a little time to liquefy.)
E. Sodium thiosulfate for 1000 mL
In 1000 mL distilled water add 6.25 g Na2S2O3.5H2O
(NOTE As the solution is unpreserved, so must be freshly prepared.)
Materials
We require Test tubes with known volume or standard Biological Oxygen Demand water sampling bottles, few Beral Pipets, use Burets or preferably 10 mL syringes and Erlenmeyer Flasks
Methodology
In this Winkler Titration method, manganous sulfate was made to react with a potassium hydroxide-potassium iodide compound mixture to give out a white flocculent precipitate of bivalent manganese i.e. manganous hydroxide
MnSO4 2 KOH Mn(OH)2 K2SO4
This precipitate was then made to react with dissolved oxygen in water to get tetravalent manganese
2 Mn(OH)2 O2 2 MnO(OH)2
Product formed, manganic basic oxide, is a brownish precipitate. Whereas if, a white precipitate comes out it indicates that no oxygen is present. Further, with acidification through sulfuric acid (or sulfamic acid, H3NSO3) the precipitate gets dissolved, forming out manganic sulfate
MnO(OH)2 2 H2SO4 Mn(SO4) 3 H2O
Formed manganic sulfate was made to react with potassium iodide yielding free iodine (I2), which gives out a brownish color. Iodine on the other side also tends to react with starch and bring into being a blue-black color which indicates the presence of iodine. This iodine can be titrated with sodium thiosulfate to give out sodium iodide, which will no further leave the brown color
2 Na2S2O3 I2 Na2S4O6 2 NaI
As a result we measured the amount of thiosulfate needed to eliminate all of the brown color, and helping in determination for total amount of I2 in the sample, and in a roundabout way giving us the amount of O2 present dissolved in
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