Analysis of a Commercial Bleach
To review oxidation-reduction reactions and their stoichiometry. To learn the concept and technique of redox titration.
To determine the percent (m/v) of an active ingredient, sodium hypochlorite (NaOCl), in a commercial bleaching agent.
B. Theoretical Background
Whereas acid-base reactions involve the transfer of a proton, oxidation-reduction or redox reactions involve the transfer of electrons from one substance to another, resulting in changes in oxidation numbers of two or more elements in the chemical reaction.
In a redox reaction the substance that donates (loses) electrons experiences an increase in oxidation number and is said to be oxidized. Such process is oxidation. Conversely, the substance that accepts (gains) electrons experiences a decrease in oxidation number and is said to be reduced. Such process is reduction. The oxidized substance is causing reduction and therefore called a reducing agent. The reduced substance is causing oxidation and therefore called an oxidizing agent.
In redox reactions the total number of electrons donated must equal the total number of electrons gained.
In today’s experiment the mass/volume percent of the active ingredient in bleach, sodium hypochlorite (NaOCl), is determined by redox titration. The method used is iodine-thiosulfate titration. It is a very useful method, since the iodide ion, I-, is easily oxidized by almost any oxidizing agent. The analysis takes place in a series of steps as follows:
1. A diluted sample of the bleach will be allowed to react with potassium iodide in acidic solution. The iodide ion will be oxidized to iodine while the hypochlorite ion will be reduced to chloride (Equation 1).
2 H+(aq) + OCl-(aq) + 2 I-(aq) ! Cl-(aq) + I2(aq) + H2O(l)
Iodine is not very soluble in water. The reaction shown in Equation 1 is carried out with a large excess of potassium iodide so that the iodine formed is converted...
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