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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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Presentation Transcript
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
objectives
Objectives
  • SWBAT:
    • Calculate the percentage of bleach in common bleach products.
    • Learn to complete titration labs
    • Learn about reduction-oxidation reactions
reactions
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

reactions1
Reactions
  • 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.
materials
Materials
  • 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
procedures
Procedures
  • 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.
procedures1
Procedures
  • 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.

www.clorox.com

procedures2
Procedures
  • Immediately after second weighing, add 100 mL of distilled water (pour it down the sides of the flask to wash down any bleach drops)

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school.discoveryeducation.com

slide12
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.

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procedures3
Procedures
  • 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.
procedures4
Procedures
  • 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.
results
Results

Mass of Na2S2O3 2.40 g

Bleach brand nameClorox Bleach

conclusion
Conclusion

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.