analysis of laundry bleach an oxidation reduction titration n.
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Analysis of Laundry Bleach: An Oxidation-Reduction Titration. Tadas Rimkus AP Chemistry Period 2. Background Information. Reduction-oxidation reactions describe all chemical reactions in which atoms have their oxidation number (oxidation state) changed.

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Analysis of Laundry Bleach: An Oxidation-Reduction Titration

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background information
Background Information
  • Reduction-oxidation reactions describe all chemical reactions in which atoms have their oxidation number (oxidation state) changed.
    • Oxidation describes the loss of electrons
    • Reduction describes the gain of electrons
background information2
Titration is a common laboratory method that is used to determine the unknown concentration of a known reactant.

A reagent, called the titrant, of a known concentration (a standard solution) and volume is used to react with a solution of the titrand, whose concentration is not known.

Background Information
  • SWBAT:
    • Calculate the percentage of bleach in common bleach products.
    • Learn to complete titration labs
    • Learn about reduction-oxidation reactions
  • You will add an excess of potassium iodide (KI) to an acidified sample of laundry bleach. The NaOCl in the bleach oxidizes the I- ion to I2. The amount of I2 produces is directly related to the original amount of NaOCl (or OCl- ions) present in the bleach:

2I- + OCl- + 2H+ I2 + Cl- + H2O

  • You will titrate the I2 produced in Reaction 1 with a standardized solution (known molarity) of sodium thiosulfate (Na2S2O3) as the titrant. Thiosulfate ion reduces the I2 ion to I- ion by the following redox reaction:

I2 + 2S2O3 2I- + S4O62-

  • The indicator is starch solution, which forms an intensely blue complex with I2. This color vanishes at the end point when the last trace of I2 is reduced.
  • Commercial laundry bleach
  • KI, 2M
  • Acetic Acid, 6M
  • Na2S2O3 5H2O
  • Starch indicator, 1%
  • 500-mL Volumetric flask
  • Stirring rod
  • Funnel
  • 50-mL buret
  • 250-mL beaker
  • Distilled water
  • Rinse and fill your cleaned buret using the sodium thiosulfate solution (Na2S2O3). Record the initial volume to the nearest 0.01 mL.
  • Clean and rinse a 250-mL Erlenmeyer flask with distilled water. Dry the outside and weigh to the nearest milligram.
  • Add 2.0-2.5 mL of bleach to the weighed flask (remove flask from scale before adding bleach)
  • Reweigh the flask to the nearest milligram.

  • Immediately after second weighing, add 100 mL of distilled water (pour it down the sides of the flask to wash down any bleach drops)

Measure out 10 mL of dilute (6 M) acetic acid (HC2H3O2) and 8 mL of 2 M KI
  • Add the acetic acid to the flask, swirl, and then add the KI solution and swirl.

  • Titrate promptly by slowly adding titrant from the buret, swirling the flask constantly.
  • When the solution has changed to a gold-orange and then to a faint yellow color, add 20 (1 mL) drops of starch indicator to turn the solution blue.
  • Rinse the inside surface of the flask with distilled water.
  • Place a piece of white paper under the flask and continue to titrate until the blue color just barely disappears.
  • Record the final buret reading.
  • In your notebook, calculate the ration R = (Volume of titrant delivered)/(Mass of bleach) in units of mL/g.
  • Refill the buret, record the buret reading, and titrate an additional bleach sample following the steps above.
  • Calculate R for the new titration
  • When finished, drain the volumetric flask and buret and rinse.

Mass of Na2S2O3 2.40 g

Bleach brand nameClorox Bleach


By calculating the two percentages of the bleach samples, we got 12.37% and 12.51% bleach by mass for Solution 1 and 2 respectively. This completed our first objective. And by completing this experiment, we learned how to do titrations and learned about oxidation-reduction reactions.