Analysis of Commercial Bleach
Introduction: Many commercial products are effective because they contain oxidizing agents. Some products that contain oxidizing agents are bleaches, hair coloring agents, scouring powders, and toilet bowl cleaners. The most common oxidizing agent in bleaches is sodium hypochlorite, NaClO (sometimes written NaOCl). Commercial bleaches are created by bubbling chlorine gas into a sodium hydroxide solution (remember this from your “funky redox rxns”?). Some of the chlorine is oxidized to the hypochlorite ion, ClO- and some is reduced to the chloride ion, Cl- (a disproportionation reaction). The solution remains strongly basic. The chemical equation for the process is: Cl2(g) + 2OH- (aq) ---> ClO- (aq) + Cl- (aq) + H2O (l)
The amount of hypochlorite ion present in a solution of bleach can be determined by oxidation-reduction titration. One of the best methods is the iodine-thiosulfate titration procedure. Iodide ion, I-, is easily oxidized by almost any oxidizing agent (It has many electrons to lose!). In an acid solution, hypochlorite ions oxidize iodide ions to form iodine, I2. The iodine that forms is then titrated with a standard solution of sodium thiosulfate. The analysis takes place in a series of steps:
1.Acidified iodide ion is added to hypochlorite ion solution, and the iodide is oxidized to iodine. 2H+ (aq) + ClO-(aq) + 2I-(aq) ---> Cl-(aq) + I2(aq) + H2O (l) 2.Iodine is only slightly soluble in water. It dissolves very well in an aqueous solution of iodide ions, in which it forms a complex ion called the triiodide ion. Triiodide is a combination of a neutral I2 molecule with an I- ion. The triiodide ion is yellow in dilute solution, and dark red-brown when concentrated. I2(aq) + I-(aq) ---> I3-(aq)
3.The triiodide is titrated with a standard solution of thiosulfate ions, which reduces the iodine back to iodide ions: I3-(aq) + 2S2O32-(aq)---> 3I-(aq) + S4O62-(aq)
During this last reaction the red-brown color...
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