In this experiment, the amount of sodium hypochlorite in a commercial bleach will be determined by reacting it with sodium thiosulfate in the presence of iodide ions and starch. A solution of sodium thiosulfate of known concentration will be added to the bleach using a buret in a titration procedure. The disappearance of the dark blue color of the starch-iodine complex will signal the end point. II. Procedures
Pre-Lab Questions 1. What is meant by a “titration”?
Titration is a technique where a solution of known (acid or base) concentration is used to determine the concentration of an unknown (acid or base) solution.
2. A solution of household vinegar (a mixture of acetic …show more content…
5. The reaction of triiodide with thiosulfate produces the dithionate ion, S4O62-. Calculate the oxidation number of sulfur in this ion. Do you think that the sulfur atoms in S4O62- all have the same oxidation number? What might the oxidation numbers be?
Oxidation number of Sulfur: 6 x -2 = -12, since the overall charge is -2, 4X + -12 = -2, 4X = 10, X = 10/4, The oxidation number of Sulfur is 5/2. These sulfur atoms do not have the same oxidation numbers, two of the sulfur atoms have a charge of 5, while the other two have a charge of 2. 6. How would each of the following laboratory mistakes affect the calculated value of the percent of NaClO in the commercial bleach (too high, too low, no change)? Explain. a. In step 1, the pipet was rinsed with distilled water immediately before being used to measure the commercial bleach solution.
If the pipet was rinsed with distilled water immediately before being used to measure the commercial bleach solution, the percent of NaClO would not change. This small amount of dilution can be ignored. b. In step 2, three grams of KI were used instead of two grams.
If three grams of KI were used instead of two, the percent of NaClO would become lower due to the even mole ratio’s. c. In step 3, some of the iodine that formed sublimed from the solution.
If some of the iodine sublimed