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ChemWiki: The Dynamic Chemistry E-textbook > Development Details > Approaches > Demos > Additional Demos > The Rainbow Connection Demonstration

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The Rainbow Connection Demonstration

Chemical Concept Demonstrated

  • Acid-base indicators

Demonstration

A colorless solution is poured into six glasses.  The liquid in the glasses is then poured back into the pitcher. rainbow.gif

Observations

Each glass produces a differently colored liquid.  When these liquids are poured back into the pitcher, the result is a colorless solution.

Explanations

Before the experiment took place, each glass was pretreated with six different mixtures of indicator, as shown below:

Red: 1.5 g phenolphthalein and 3.0 g m-nitrophenol

Orange: .45 g phenolphthalein and 6.0 g m-nitrophenol

Yellow: 6.0 g m-nitrophenol

Green: .6 g thymolphthalein and 6.0 g m-nitrophenol

Blue: 1.5 g thymolphthalein

Violet: .9 g phenolphthalein and .4 g thymolphthalein

These indicator solutions were all then allowed to evaporate into a thin film at the bottom of each glass, rendering them invisible.

The solutions change color because a basic solution is added to each glass.  All of the indicator mixtures are colorless under acidic conditions and change color under basic conditions.

At the end of the demonstration, the solutions are poured together into a second pitcher that contains a powerful acidic solution.  Because the indicators are colorless under acidic conditions, the contents of all of the glasses mix with the acidic solution to form a single, colorless solution.

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Last Modified
10:31, 2 Oct 2013

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