Dissolve Oxygen Lab Report

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Winkler Method for Dissolve Oxygen

I. INTRODUCTION
They are two ways of determining dissolve oxygen in water the titrimetric by Winkler and electrometric. Winkler method is a technique used to measure dissolved oxygen in freshwater systems. Dissolved oxygen is used as an indicator of the health of a water body, where higher dissolved oxygen concentrations are correlated with high productivity and little pollution. This test is performed on-site, as delays between sample collection and testing may result in an alteration in oxygen content. The process includes divalent manganese salt precipitation by strong alkali to divalent manganese hydroxide. Next is the addition of potassium iodide or potassium hydroxide to create a pinkish brown precipitate.
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The sodium thiosulfate was standardized by titration with potassium dichromate dissolved into 50ml that has 1ml H2SO4 and 0.2g Na2CO3 and 0.5g potassium iodide that was allow to stand a while. The solution was titrated until the yellowish color was completely disappeared. Then 1ml of starch solution is added it became dark blue. The titration with thiosulfate was then continue until the dark blue color was disappear making the solution colorless. In the preparation of 2.4M manganese(II)sulfate solution 20.5g of MnSO4 ▪ H2O was dissolved in 50ml distilled water then it was transferred to amber bottle. On the preparation of alkaline iodide solution 7.5g of potassium iodide and 21g of potassium hydroxide was dissolved into 50ml distilled water then it was stored in amber bottle. Before the titration of water sample, all the solution and reagent was prepared, the groups collected water sample using BOD bottles. The bottles were submerged for about 30seconds avoiding introduction of air bubbles and turbulence. After that, the water sample was fixed using 2ml manganous sulfate and alkaline iodide. The bottle was shook then allow the brown precipitate to settled after all brown precipitate settled 2ml of sulfuric acid was added. The stopper was replaced then the bottle was shook again until all precipitate was completely dissolved. As the water

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