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Redox Titration of Bleach

Analysis of bleach involves two sequential redox reactions: First, bleach is reacted in acid solution with excess iodide anion to produce yellow-colored iodine:

ClO−+2H++2I−→I2+Cl−+H2O

Then, to determine how much of the iodine was formed, the solution is titrated with sodium thiosulfate solution:

I2+2S2O32−→2I−+S4O62−

A bit of starch is added to the titration reaction. Starch is intensely blue in the presence of I2. The solution thus turns from deep blue to colorless at the reaction equivalence point.

A sample of a new cleaning product, “Joe’s Famous Bleach Cleaner”, with a mass of 65.0g , was diluted with an acetic acid solution containing excess I−. A small amount of starch indicator solution was then added, turning the solution a deep bluish-purple. The solution was then titrated with 0.100M thiosulfate, S2O32−. A volume of 40.0mL of thiosulfate, the titrant, was needed to turn the solution colorless.

What is the percentage composition by mass of NaClO in the bleach product?

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Posted on September 25, 2013, in #question and tagged , , , , . Bookmark the permalink. 1 Comment.

  1. .1M(.04L)=.004MS2O3
    .004/2=.002
    .002(74.4422) = .1488
    .1488/65.0g = .00229
    .00229(100) = .229%

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