Bleach Lab Report - Lab PDF

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Ashley Campoverde Chemistry 2003 BMWF Professor Olga Lavinda October 15, 2019 Lab Report: Bleach Titration Lab Abstract The experiment was conducted to determine the mass percent of sodium hypochlorite in commercial bleaching solution by titrating a standardized solution of sodium thiosulfate of 0.080402 M. The study found a mass percent of 4.35% sodium hypochlorite in bleaching solution. Introduction In the following experiment conducted, we determined the percent of sodium hypochlorite in commercial bleaching solution by titrating a standard sodium thiosulfate solution with a molarity of 0.080402 M into diluted bleaching solution. By using iodine as an indicator, we are able to watch NaOCl reduce iodine to I2. We were able to determine how much iodine was in the solution by titrating sodium thiosulfate. Also, we’re able to quantitatively measure the results, as well as see visible changes occur. Equation 1: OCl-(aq, colorless) + 2I-(aq, colorless) + 2H3O+(aq) -> I2 (aq, brown)+ Cl-(aq, colorless)+ 3H2O(l) It is possible to measure the amount of iodine produced by this reaction through a redox titration with a solution of thiosulfate ion. Equation 2: I2 (aq, brown) + 2S2O32-(aq. colorless) -> 2I-(aq,colorless)+ S4O62-(aq, colorless) A color change occurs when the thiosulfate combines with the iodine solution as the solution begins a deep brown color, and then changes to clear as the reaction products, I-(aq) and tetrathionate ion, are both clear. Starch can be added to see this color change more clearly. The number of moles of thiosulfate can be determined through the titration, which leads to the number of moles of iodine, which allows the determination of the moles of hypochlorite in the diluted bleach, and finally the number of moles in the undiluted bleach solution. 1. End point: The point in a titration usually noting the completion of a reaction and signaled by the indicator, when it changes color. 2. Indicator: Any substance that gives a visible sign, in this case, change in color to indicate that the titration is complete. 3. Molarity: is the number of moles of solute per liter of solution. Used to express the concentration of a solution. 4. Neutralization reactions: A type of chemical reaction of an acid with a base to produce salt and water. 5. Oxidizing Agent: a substance that tends to bring about oxidation by being reduced and gaining electrons. 6. Redox Reaction: is a type of chemical reaction that involves a transfer of electrons between two species. 7. Reducing Agent: is an element or compound that loses an electron to another chemical species in a redox chemical reaction 8. Standard solution: a solution containing a known concentration of solute. 9. Titration: is the measurement of the volume of a standard solution required to completely

Ashley Campoverde Chemistry 2003 BMWF Professor Olga Lavinda October 15, 2019 react with a measured volume or mass of the substance being analyzed. Data, Results, and Calculations Column 4 are blank on data sheet because the volume of S2O32- used was consistent in trials 1-3, so no further trials were needed. Average of Volume of S2O32-: 15ml + 14 ml + 14.7 ml= 14.6 ml (Number of moles of S2O32- required, mol)= (Volume of S2O32- solution used, mL)(1L/1000mL)(concentration of S2O32- solution, mol L-1) Number of moles of S2O32-, mol=14.6mL x (1 L/1000 mL) x (0.080402 mol/L)= 0.00117 mol S2O32Answer: 1.17 x 10-3 mol S2O32Number of moles of I2, mol= (Number of moles of S2O32- required, mol)( 1mol I2/ 2mol S2O32-) 1.17 x 10-3 mol S2O32- x (1mol I2/ 2mol S2O32-) = 5.85 x 10-4 mol of I2 Number of moles of OCl-, mol= (Number of moles of I2)( 1mol of OCl-/1 mol of I2) 5.85 x 10-4 mol of I2 x (1mol of OCl-/1 mol of I2)= 5.85 x 10-4 mol of OClConcentration of OCl- in concentrated bleach, mol L-1= (number of moles of OCl- in concentrated bleach, mol)/(volume of concentrated bleach sample, L) Concentration of OCl- in concentrated bleach, mol L-1= (5.85 x 10-4 mol of OCl-) /(0.01 L)= 0.0585 M = 5.85 x 10-2 M Mass of NaOCl= 22.990g + 15.999g + 35.453g =74.44 g mass %= (mass of NaOCl/mass of bleach solution) x 100% mass of NaOCl in bleaching solution, g= (5.85 x 10-4 mol of OCl-)(1mol of NaOCl/1 mol of OClion)(74.44g NaOCl/1 mol NaOCl)= 0.0435 g= 4.35 x 10-2g of NaOCl mass %= (4.35 x 10-2g of NaOCl / 1 g/ml) x 100%= 4.35 %

Limits on Results: • Buret measures +/- 0.05mL • Triple beam balance measures +/- 0.05g • Analytical balance +/- 0.0001g (less than 60 grams)

Ashley Campoverde Chemistry 2003 BMWF Professor Olga Lavinda October 15, 2019 +/- 0.001g (60 to 160g) • 100 mL graduated cylinder measures +/- 0.05mL Conclusion In the experiment, a redox titration was performed in order to determine the percent of sodium hypochlorite in commercial bleach. This is done by reacting the bleach with sodium thiosulfate in company with iodide ions and starch. The concentration of sodium thiosulfate is already known, and calculations can be done in order to calculate the percent by mass of NaClO in commercial bleach. An average of 14.6 mL of sodium thiosulfate was used in the titration procedure, which amounts to a percent of 4.35%, and 6% of the commercial bleach is sodium hypochlorite. There was the potential of many errors in this experiment. Mainly, these errors are focused on contamination. A total of four different solutions were used, and any mixture between could have resulted in different solutions and concentrations. This could have resulted in a different titration scheme, and a different percent of sodium hypochlorite would have been calculated. Similarly, the amount of distilled water used in this experiment would have a profound impact on the final percentage calculation. For example, the commercial bleach solution was originally 10 mL, but was diluted in a 100 mL volumetric flask. Any addition of distilled water, whether it was by inaccurate measurement, or because of equipment cleaning, could have skewed the molarity and therefore, the number of moles used in calculations. If there was too much distilled water, then the molarity and moles would seem lower, yielding a lower percentage calculation. Overall, the results of the experiment are fairly precise and accurate. Multiple trials were performed, so precision was enhanced. In order to improve accuracy and/or precision, better equipment could have been used....