We're going to do a titration to determine the mass percent of sodium hypochloride in commercial bleach. We're going to prepare a diluted solution of bleach and pipe it at a 25-millimeter sample of that dilute solution. We're going to react that solution with an excess of potassium iodide. Iodin will be produced. We'll titrate the iodine produced with a standardized solution of sodium thylsulfate. The volume and the molarity of the sodium thylsulfate solution using the titration will allow you to calculate the moles of thylsulfate used, the moles of iodine produced, and the moles of hypochloride in your dilute bleach solution. This will allow you to calculate the number of grams of sodium hypochloride in the dilute solution, and the number of grams of sodium hypochloride in the concentrated solution. You can use that data to calculate the mass percent of sodium hypochloride in the bleach. We're going to pipe that 5 milliliters of the commercial bleach solution into 100 milliliters of volumetric flask. We're going to add distilled water, and we're going to fill the flask until the bottom of the meniscus reaches the line on the volumetric flask. We will then stop with the flask and mix the solution so that it is homogeneous. We're going to pipe that 25 milliliters of our diluted bleach solution into a 250 milliliters of water. We're going to add a small amount of water, roughly about 20 milliliters of water, to the flask to give us a little bit of additional volume. We're going to add 2 milliliters of 3-mole HCl to our reaction mixture. We're going to add 2 grams of solid potassium iodide to the reaction mixture. The solution will turn a reddish orange color due to the formation of iodine. The hyperchloride in the bleach oxidizes I- to I2. We're going to titrate the iodine produced with a standardized solution of sodium thiosulfate. The sodium thiosulfate will reduce the iodine back to iodide. We'll take an initial buret reading. We'll slowly add the thiosulfate solution until the reaction mixture is a real pale yellow color. You should rinse down the walls of the flask periodically to make sure that everything has a chance to react. We're going to titrate to a very light yellow color and then we're going to add several drops of starch indicator solution. The solution will turn blue due to the formation of a complex between the iodine and the starch. We will continue the titration until the blue color disappears. We'll then take a final buret reading and determine the total number of milliliters of sodium thiosulfate solution added to the reaction mixture.