Essay About Ascorbic Acid And Thiosulfate Solution

The Indirect Iodometric Analysis of Ascorbic Acid
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The Indirect Iodometric analysis of Ascorbic AcidUnknown number 780++I. Purpose: To determine the weight percent of ascorbic acid in an unknown sample by indirect iodometric analysis. This is done by reacting ascorbic acid with triiodide and then titrating with standardized thiosulfate solution. II. Theory: A known concentration of potassium iodate and excess potassium iodide is used in titration to standardize the thiosulfate solution. This process with calculations will give the concentration of standardized thiosulfate solution which is used to titrate the ascorbic acid unknown sample. To titrate the unknown, potassium iodate solution and excess potassium iodide are mixed to form triiodide. This reacts with Ascorbic Acid to form dehydroascorbic acid. The excess triiodide is then titrated with standardized thiosulfate and ascorbic acid moles can be calculated from the known moles of iodate and the volume and concentration of triiodide. III. Sample Calculations:Concentration of the KIO3 [pic 1]Net Ionic equationsa) the reaction of iodate with iodideIO3- + 8I- + 6 H+ → 3I3- + 3 H2Ob) the reaction of triiodide with thiosulfate2S2O3-2 + I3- → S4O6-2 + 3 I-c) the reaction of ascorbic acid with triiodideC6H8O6 + I3-  + H2O → C6H6O7 + 3I- + 4H+ Concentration of the standardized thiosulfate solution[pic 2][pic 3]Weight percent of Ascorbic Acid in Unknown[pic 4][pic 5][pic 6][pic 7][pic 8]Ascorbic acid concentration 0.00256 M Ascorbic Acid[pic 9]IV. Data and ResultsMass Na2S2O4 1.7050 gMass KIO3 0.2020Concentration KIO3 0.009439 MStandardization of Thiosulfate[pic 10]FlaskKI (g)Thiosulfate added (L)M Thiosulfate20.49950.0037900.07471530.50520.0038650.07326540.49860.0038800.072982        Titration of Ascorbic AcidFlaskUnknown amount (g)KI (g)Thiosulfate titrant added (L)I3- Reacted (mol)Ascorbic Acid (g)Ascorbic Acid MWeight % Ascorbic Acid10.15270.49360.0059100.0002071190.0364780.00255923.88940.15510.50200.0054510.0002240560.0394610.00278525.4423(auto)0.15320.49930.0060220.0002030280.035757N/A23.340[pic 11]FW Ascorbic Acid 176.12 gTitration curve Graph 1[pic 12][pic 13][pic 14]IV. Conclusion: The unknown provided an ascorbic acid content of 24% by weight. The autotitrator stirrer got stuck for the first trial so it had to be repeated. The second trial was kept. However, since a significant amount of thiosulfate solution was used in this process, the final trial (flask 4) of the manual titration needed 1mL of another thiosulfate solution. This could have provided contamination error. This could have provided error in the weight percent of ascorbic acid. It is possible that some measured dry solids were not fully transferred or entirely dissolved in solution which could have provided error.Autotitration Data and CalculationsVolume V (mL)Voltage E (V)ΔV (mL)ΔE (V)Δ E /Δ V(V/mL)▽ (mL)▽Δ (mL)Δ (Δ E/Δ V)(V/mL)Δ (Δ E/Δ V)/ Δ▽ (V/mL2)Vavg (mL)00.38880.01-0.0002-0.020.0050.010.0110.010.010.38860.01-0.0001-0.010.0150.010.0110.020.020.38850.01000.0250.193-0.00027-0.001380.12150.030.38850.376-0.0001-0.000270.2180.599-0.00752-0.012550.51750.4060.38840.822-0.0064-0.007790.8170.7160.0038510.0053791.1751.2280.3820.61-0.0024-0.003931.5330.656-0.00048-0.000731.8611.8380.37960.702-0.0031-0.004422.1890.697-0.00136-0.001962.53752.540.37650.692-0.004-0.005782.8860.674-0.00047-0.00073.2233.2320.37250.656-0.0041-0.006253.560.648-0.00172-0.002653.8843.8880.36840.64-0.0051-0.007974.2080.619-0.0039-0.006314.51754.5280.36330.598-0.0071-0.011874.8270.535-0.01016-0.018995.09455.1260.35620.472-0.0104-0.022035.3620.361-0.02077-0.057525.54255.5980.34580.25-0.0107-0.04285.7230.178-0.07607-0.427355.8125.8480.33510.106-0.0126-0.118875.9010.063-0.07113-1.129085.93255.9540.32250.02-0.0038-0.195.9640.02-0.095-4.755.9745.9740.31870.02-0.0057-0.2855.9840.018-0.17125-9.513895.9935.9940.3130.016-0.0073-0.456256.0020.014-0.83542-59.67266.0096.010.30570.012-0.0155-1.291676.0160.011-4.70833-428.036.02156.0220.29020.01-0.06-66.0270.014.14106.0326.0320.23020.01-0.019-1.96.0370.011.211216.0426.0420.21120.01-0.0069-0.696.0470.010.32326.0526.0520.20430.01-0.0037-0.376.0570.0310.2046156.6004966.07256.0620.20060.052-0.0086-0.165386.0880.0770.0957771.2438546.12656.1140.1920.102-0.0071-0.069616.1650.1510.0361080.2391256.24056.2160.18490.2-0.0067-0.03356.3160.2620.015290.0583596.4476.4160.17820.324-0.0059-0.018216.5780.3860.0066030.0171066.7716.740.17230.448-0.0052-0.011616.9640.4930.0030570.0062017.21057.1880.16710.538-0.0046-0.008557.4570.406-0.00167-0.004117.667.7260.16250.274-0.0028-0.010227.86380.1597