Experiment 8 the Analysis of Household Bleach Essay

3655 Words Mar 20th, 2015 15 Pages
Experiment 8: Redox: Analysis of the Oxidizing Capacity of Bleach
PURPOSE
In this experiment, you will show how redox reactions can be used to quantitatively determine the amount of oxidizing agent in liquid hypochlorite household bleach.
There are two oxidation-reduction reactions for determining the oxidizing capacity of bleach. Initially an excess of iodide ions are added to a bleach solution. The iodide ions are oxidized to iodine after the solution has been acidified. Starch is added to the resulting iodine solution as an indicator. The solution is then titrated with sodium thiosulfate until the color of the solution changes indicating the endpoint of the reaction. Data collected from the titrations will be used to calculate the
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The iodide ions, I–, are oxidized to iodine, I2, (see equation [1]). After the solution is acidified – the addition of a strong acid to the solution will cause the conversion of the hypochorite ion to hypochlorous acid. The iodine that is formed is then titrated with sodium thiosulfate, Na2S2O3, solution that reduces the iodine to iodide (see equation [2]).
1) Acidified iodide ion is added to hypochlorite ion solution and the iodide is oxidized to iodine by the hypochlorite ion.
HOCl (aq) + 2I− (aq) + H+ (aq) → I2 (aq) + Cl− (aq) + H2O(l) [1]
a. The iodine produced forms a complex ion called the triiodide ion with any excess iodide ions. Triiodide is a combination of a neutral I2 molecule with an I- ion. The triiodide ion is yellow in dilute solution.
I2 (aq) + I– (aq) → I3– (aq) (yellow solution) [105]

CH204 Experiment 8: The Analysis of Household Bleach spring 2015
The triiodide is titrated with a standard solution of thiosulfate ions, which reduces the iodine back to iodide ions. I3-(aq) + 2 S2O32-(aq) → 3 I-(aq) + S4O62-(aq)
2) The overall stoichiometry of the two reactions is given in equations [1] and [2].
2S O2− (aq) + I (aq) → 2I− (aq) + S O 2− (aq) [2] 23246
Starch is used as an indicator and it is added near the endpoint where the concentration of iodine is low and the iodine solution has changed to a pale or light yellow. When the starch is added, the yellow color will change to a blue

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