existed inside the sample consumed oxygen for respiration The Winkler method

Existed inside the sample consumed oxygen for

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existed inside the sample consumed oxygen for respiration. The Winkler method utilized the following chemicals namely: Manganese Sulfate (MnSO 4 *2H 2 O), which was the source of Mn ions; KI, the source of Iodide ions; KIO 3 , the primary standard; H 3 PO 4 ,;NaOH; Na 3 N,;Na 2 S 2 O 3 *5H 2 O,; the source of thiosulfate ions. The experiment made use of 50 mL burettes, 50-,100-mL beakers, watch glass, 1-mL syringe, 250 mL Erlenmeyer flask, 250 mL volumetric flask, Analytical balance, Top-loading balance, and hot plate. Solution preparation was done during the first day of the experiment. These include 25 mL 4.0 M MnSO 4 from MnSO 4 *2H 2 O crystals, which the calculated and weighed amount (18.7 g) was dissolved in 10 mL distilled water and filtered into a 25 mL volumetric flask; 25 mL 18 M NaOH solution with 5g KI and 0.15g NaN 3 , 250 mL
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R. J. C. De Guzman / Chemistry 26.1 (2017) P a g e | 2 0.125 M stock Na 2 S 2 O 3 , 500 mL 0.5 M H 2 SO 4 . Starch solution was freshly prepared by weighing 1.0 g starch, dissolved, and poured in approx. 100 mL distilled water and kept at 90°C- 100°C. The 250 mL 0.0125 M standard Na2S2O3 solution from 0.125 M stock Na2S2O3 was done by group. In the standardization of Na 2 S 2 O 3 , 0.15 g KIO 3 was weighed using a 50 mL beaker and then dissolved with distilled water. It was then transferred quantitatively into a 100 mL volumetric flask, diluted, covered with parafilm, and mixed. 10 mL was taken out and put in three Erlenmeyer flasks, labelled properly. 20 mL distilled water was poured in each flask. 1.0 g KI and 10 mL 0.5 H 2 SO 4 was added in each flask. Using Na2S2O3 as standard, with a 0.011298307 M, titrated the solution until pale yellow. Immediately added 1.0 mL starch solution and then continue titration until complete disappearance of blue color. Afterwards, standardization was performed in triplicate. In the analysis of the water sample, a syringe was used to add 0.5 mL MnSO 4 solution and 0.5 mL NaOH with KI and NaN 3 solution without producing air bubbles inside the sample then 2.0 mL of concentrated H 3 PO 4 using a pipette was added. The pipette should be below the surface of the water. The solution was covered again and mixed and left alone for 10 minutes. Aliquot taken out was 50.0 mL and transferred in a 250 mL Erlenmeyer flask. Using Na 2 S 2 O 3 as standard, with a 0.011298307M, titrated the solution until pale yellow. Immediately added 1.0 mL starch solution and then continue titration until complete disappearance of blue color. All sample triplicate were performed and the collected data was expressed in 2.049 ppm. Results and Discussions The chemical reactions in this experiment are (1) + ¿ + ¿ 3 I 3 + 3 H 2 O + K ¿ ¿ + 6 H ¿ ¿ + 8 I ¿ KIO 3 ¿ (2) ¿ ¿ + 3 I ¿ ¿ →S 4 O 6 2 ¿ ¿ + I 3 ¿ 2 S 2 O 3 2 ¿ (3) ¿ →Mn ( OH ) 2 + ¿ + 2 ( OH ) ¿ M n 2 ¿ (4) 4Mn(OH) 2 + O 2 4MnO(OH) + 2 H 2 O (5) + ¿ + I 2 + 4 H 2 O ¿ 2 M n 2 ¿ + ¿ + 2 MnO ( OH ) + 2 I ¿ 6 H ¿ (6) ¿ ¿ →I 3 ¿ I 2 + I ¿ (7) ¿ ¿ →S 4 O 6 + 3 I ¿ 2 ¿ + I 3 ¿ 2 S 2 O 3 ¿ The standard used for the titration was thiosulfate (S 2 O 3 ) and the pertinent chemical reactions are (1) and (2). In reaction (1), excess
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  • Fall '17
  • Sir Jaden Smith
  • R. J. C. De Guzman

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