Beyond the ‘blue bottle’

The ‘blue bottle’ demonstration is one of the most well-known and best-loved chemistry demonstrations. A flask containing a colourless liquid (consisting of an alkaline solution of glucose and methylene blue) is shaken. The resulting increase in dissolved oxygen concentration oxidises the colourless form of the dye back to the blue form, until the glucose reduces it once again.

Despite the fact that instructions for this demonstration often suggest using other dyes, it’s uncommon for teachers to do so. This is a great shame, because these dyes can produce some really beautiful colour changes. Presumably this is because methylene blue is commonly used in schools for other experiments. However, indigo carmine is very cheap, safe, easily obtained and produces a range of stunning colours.

This demonstration can be used to support teaching of redox topics, as well as illustrating aspects of colour chemistry. The more I researched what was happening, the more interesting things emerged.

With an accompanying video, Declan Fleming takes you through this demonstration from preparation to presentation, and suggests how it can be adapted for various teaching goals.