Color-change demonstrations are classic fare for the chemistry classroom. The most common color change reaction may be the Blue Bottle (blue-clear-blue) chemistry demonstration and the Briggs-Rauscher oscillating clock (clear-amber-blue), but if you use different indicators you can get color-change reactions to suit just about any occasion. For example, you can perform a green-red-green color change reaction for a bit of Christmas chemistry. This color change demonstration uses the indigo carmine indicator:
- Prepare a 750 ml aqueous solution with 15 g glucose (solution A) and a 250 ml aqueous solution with 7.5 g sodium hydroxide (solution B).
- Warm solution A to around body temperature (98-100°F).
- Add a 'pinch' of indigo carmine, the disodium salt of indigo-5,5'-disulphonic acid, to solution A. A pinch is enough indicator to make solution A visibly blue.
- Pour solution B into solution A. This will change the color from blue → green. Over time, this color will change from green → red/golden yellow.
- Pour this solution into an empty beaker, from a height of ~60 cm. Vigorous pouring from a height is essential in order to dissolve oxygen from the air into the solution. This should return the color to green.
- Once again, the color will return to red/golden yellow. The demonstration may be repeated several times.