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The Red-White-and-Blue Demonstration

  • Page ID
    3089
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    Chemical Concepts Demonstrated

    • Kinetics
    • Multi-step reactions

    Demonstration

    Three solutions are combined in alphabetical order.
    • Solution A: Na2SO3 * H2O dissolved in water mixed with 2,4,2',4',4"-pentamethoxytriphenyl methanol dissolved in acetone.
    • Solution B: Cd(NO3)2 * H2O and HCl added to water, shaken, and diluted.
    • Solution C: NaIO4 dissolved in water.
    beaker.gif

    Observations

    Solutions A and B produce a red solution. Adding solution C after this turns the solution milky white, then blue after a time.

    Explanations (including important chemical equations)

    The hydrochloric acid in solution B turns the 2,4,2',4',4"-pentamethoxytriphenyl methanol (an indicator) red. The addition of solution C causes the pH to increase due to the formation of OH- ions in the IO4- oxidation of S2O32-.

    2 S2O32- (aq) + IO4- (aq) + H2O (l) --> S4O62- (aq) + IO3- (aq) + 2 OH- (aq)

    When the indicator turns colorless again, the milky-white suspension of Cd(IO4)2+ becomes apparent. The further increase in pH triggers another indicator (thymolphthalein), turning the solution blue.

    Contributors


    The Red-White-and-Blue Demonstration is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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