Chemical Riddle #2

A student of mine, Anthony Shepherd, and I worked together to develop a new chemical riddle.  How do you think we performed the experiment in the video below?


We look forward to hearing your hypotheses!

Editor Note: See the Solution to Chemical Riddle #2. (Accessed 5/7/14)


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Comments 1

Andres Tretiakov's picture
Andres Tretiakov | Fri, 05/02/2014 - 02:47

Hi Tom,

This reminds me of the Rainbow Connection demo for acids and alkalis I do regularly. The 'sponge' paint brush is pre-soaked initially in a weak acid solution (say HCl 1 M for example). The beakers have each an acid-base indicator which is coloured in alkaline conditions but colourless under acidic conditions. All you need to do is place the 'acidic' sponge in each beaker and swirl the contents until the colour disappears.

Did I get it right?

An alternative would be to place another sponge paint brush pre-soaked in an alkaline solution and turn colourless solutions into bright different colours. Then one by one or two by two the coloured solutions could be added into a bigger taller beaker (2-5 L) which has a few drops of conc. HCl at the bottom, all the coloured solutions would turn courless again!

Hope that helps,