1. A student measured the amount of dissolved oxygen in river water sample using Winkler titration method. The titration reaction is described by the following equation. I2 (g) + 2Na2S2O3 (aq) -> 2NaI (aq) + Na2S4O6 (aq) a. Calculate the concentration of the iodine solution in given that 9.0 ml of the 0.02 M sodium thiosulfate solution were required in the titration for complete reaction with 50 ml portions of the iodine solution. b. For every 1 mole of oxygen gas (O2) in the water sample 2 moles of iodine (I2) are liberated in this experiment. Calculate the concentration of dissolved oxygen in the water sample in ppm. (Hint: don't use the equation provided in the handout to calculate the concentration of the dissolved oxygen) (3 marks)
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Given that 9.0 ml of 0.02 M sodium thiosulfate solution were used: Moles of sodium thiosulfate = 0.02 mol/L * 0.009 L = 0.00018 moles Show more…
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A lump of impure iodine, I2, of mass 0.4000 g was ground to powder and dissolved in potassium iodide, KI, solution. The solution was made up to 250.00 cm^3. 25.00 cm^3 of this solution was then titrated with 0.01 mol dm^-3 sodium thiosulfate (Na2S2O3) solution which converted to S4O6^2-. The mean titre was 26.00 cm^3. (a) Give the oxidation states of sulfur in S2O3^2- and in S4O6^2-. (b) Write balanced half-equations for this reaction. (c) Write the overall redox equation for this reaction. (d) Name the oxidizing and reducing agent of this reaction. (e) How many moles of sodium thiosulfate were used in the titration? (f) Calculate the number of moles of iodine, I2, in 25.00 cm^3 of solution. (g) Calculate the number of moles of iodine in 250.00 cm^3 of solution. (h) Calculate the mass of iodine present in part (g). (i) Calculate the percentage purity of iodine. (j) How would you expect the presence of an air bubble in your burette to impact your percentage purity calculation in part (i)? Would it lead to an overestimation or an underestimation of your calculated value? Explain your answer.
Adi S.
Sodium thiosulfate, Na2S2O3, is an important reagent for titrations. Its solutions can be standardized by titrating the iodine released when a weighed amount of potassium hydrogen iodate, KH(IO3)2 (389.912 g/mol), is allowed to react with excess potassium iodide in acidic solutions. The net ionic equations are: production of iodine from KH(IO3)2: IO3- + 5I- + 6H+ -> 3I2 + 3H2O; titration of iodine: I2 + 2S2O3^2- -> 2I- + S4O6^2-. What is the molarity of a sodium thiosulfate solution if 29.65 mL are required to titrate the iodine released from 0.1583 g of KH(IO3)2?
8.. Sodium thiosulfate, Na2S2O3, is an important reagent for titrations. Its solutions can be standardized by titrating the iodine released when a weighed amount of potassium hydrogen iodate, KH(IO3)2 (389.912 g/mol), is allowed to react with excess potassium iodide in acidic solutions. The net ionic equations are: production of iodine from KH(IO3)2: IO3 – + 5 I– + 6 H+ → 3 I2 + 3 H2O titration of iodine: I2 + 2 S2O3 2– → 2 I– + S4O6 2– What is the molarity of a sodium thiosulfate solution if 30.91 mL are required to titrate the iodine released from 0.1007 g of KH(IO3)2?
Sarah P.
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