Congratulations to Andres Tretiakov who solved Chemical Riddle #2. In this particular riddle, we presented a twist on the famous “Disappearing Rainbow” demonstration. You can purchase a pre-packaged version of this demonstration from Flinn Scientific.
To conduct this demonstration, six beakers are arranged with different acid-base indicator mixtures as follows:
Beaker 1 contains an indicator mixture that is red in base and colorless in acid.
Beaker 2 contains an indicator mixture that is orange in base and colorless in acid.
Beaker 3 contains an indicator mixture that is yellow in base and colorless in acid.
Beaker 4 contains an indicator mixture that is green in base and colorless in acid.
Beaker 5 contains an indicator mixture that is blue in base and colorless in acid.
Beaker 6 contains an indicator mixture that is violet in base and colorless in acid.
Prior to the start of this experiment a very small amount of acid is poured into each beaker, rendering the contents of each beaker colorless. To start the demonstration, a solution of base is poured into each beaker, which causes the color of each indicator mixture to be displayed. After this, a sponge paint brush that has been soaked in acid is swirled into the contents of each beaker. Of course the contents of each beaker turn colorless as a result. Finally, a sponge paint brush that contains base is swirled into the contents of each beaker and the color returns!