Analysis of Laundry Bleach: An Oxidation-Reduction Titration

1. Analysis of Laundry Bleach: An Oxidation-Reduction Titration Tadas Rimkus AP Chemistry Period 2

2. 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

3. Background Information

4. 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

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

6. 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

7. 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.

8. 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

9. 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.

10. 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

11. 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) www.npwd.org www.merriam-webster.com school.discoveryeducation.com

12. 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. upload.wikimedia.org www.merriam-webster.com vitaminsbeautycare.com

13. 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.

14. 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.

15. Results Mass of Na2S2O3 2.40 g Bleach brand nameClorox Bleach

16. 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.