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ChemWiki: The Dynamic Chemistry E-textbook > Development Details > Approaches > Demos > Additional Demos > The Red-White-and-Blue Demonstration

The Red-White-and-Blue Demonstration

 

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 OHions 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.

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Last Modified
10:31, 2 Oct 2013

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