The whoosh bottle

Description:

Vapour in a large bottle is ignited resulting in a large blue flame and a “whoosh” sound. After the bottle has cooled, the water vapour condenses and may be poured out.

Requires:

  • Methanol or surgical spirits (a mixture of ethanol and methanol)
  • An empty 20 L water cooler bottle
  • A remote source of ignition such as a long lighter

Method:

Pour a small amount of alcohol into the water cooler bottle. Swill the liquid around so that it evaporates and fills the bottle with vapour. Pour the excess liquid out of the bottle. With the bottle on the floor (and upright) ignite the vapour from a safe distance. Allow the bottle to cool slightly, which will allow water vapour generated in the reaction to condense. The small amount of condensed water can then be poured out of the bottle. This shows the water produced in a combustion reaction in addition to the carbon dioxide.

Principle:

The intimate mixture of alcohol vapour and air means that the combustion takes place very quickly. The reaction is an exothermic reaction generating heat, light and sound.
Parallels may be drawn with combustion in a motor car where an intimate mixture of vapour and air is also produced. The flame has a lot of blue colouration and advanced learners may be interested to know that this is an emission from excited radicals produced in the combustion reaction.

Tips:

If you intend to repeat the experiment first ensure that the carbon dioxide produced in the first reaction is cleared from the bottle and second give the bottle plenty of time to cool down. If the bottle is full of carbon dioxide from the first ignition the flame will only burn in the neck of the bottle, which slowly melts the bottle.
Companies that supply water coolers and replenish water will may have reject bottles that are destined for recycling. These are great for such demonstrations and often come at no cost.
A 2 L soda bottle can be substituted for the large water cooler bottle. The sound and light are not so dramatic but the principle is the same.

Safety:

Ignite the vapours from a safe distance with a long lighter or a splint on a stick. Ensure the bottle of alcohol used to charge the demonstration is closed and any excess alcohol poured out is at a safe distance before igniting a flame.

Tags: Exothermic, light, combustion, whoosh bottle.