To find the amount of hypochlorite ion present in a solution of bleach using oxidation-reduction titration. II Procedure: 1) Dilute the concentrated bleach. Use a pipet bulb and a 5-mL transfer pipet to measure 5.00mL of a commercial bleach solution into a 100mL volumetric flask. Dilute to the mark with distilled water, stopper and mix well. 2) Measure the potassium iodide. Weigh out approximately 2 g solid KI. This is a large excess over that which is needed. 3) Oxidize the Iodide ion with Hypochlorite ion. Pipet 25mL of the dilute bleach into an Erlenmeyer flask. Add the solid KI and about 25mL of distilled water. Swirl to dissolve the KI. Work in a fume hood and slowly, with swirling, add approximately 2mL of 3 M HCl. The solution should be dark yellow to red-brown from the presence of the I 3- complex ion. 4) Titrate the iodine. Record the initial buret reading. Titrate with a standard .10 M sodium thiosulfate solution until the iodine color becomes light yellow. Add one dropper of starch solution. The blue color of the starch-iodine complex should appear. Continue the titration until one drop of Na 2 S 2 O 2 solution causes the blue color to disappear. Record the final buret reading. 5) Repeat Repeat the titration beginning with step 2 two more times. III Data Collection: Initial buret reading: 50 ml Final Buret reading 1 (Turned yellow): 26.0 ml Final Buret reading 2 (Turned yellow): 27.5 ml Final Buret reading 3 (Turned yellow): 25.1 ml Final Buret reading 4 (Turned yellow): 24.5 ml Final Buret reading 1 (turned blue): 0.5ml later Final Buret reading 2 (turned blue): 0.7ml later Final Buret reading 3 (turned blue): 0.5ml later Final Buret reading 4 (turned blue): 0.3ml later IV Data analysis: Data and Calculations 1) Use the equations given to determine the number of moles of sodium thiosulfate that are equivalent to one mole of sodium hypochlorite. 1 mol ClO(-)
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