Another demonstration that involves a bit of trickery with the audience (see Beakers not Conicals and the Law of similar shapes).
A solution of ammonia is poured into each of three beakers which contain (unknown to the audience) a little phenolphthalein, a little lead nitrate solution and a little copper sulphate solution respectively. The beakers’ contents turn red, milky white and deep blue respectively. Pouring the contents of the beaker into acid reverses the changes to give a colourless solution.
Red, White and Blue
Red, White and Blue – Risk Assessment