TeacherExpt:The ‘Whoosh’ bottle demonstration
From Learn Chemistry Wiki
This procedure is designed as a demonstration to be performed by a teacher or other qualified person.
A mixture of alcohol and air in a large polycarbonate bottle is ignited. The resulting rapid combustion reaction, often accompanied by a dramatic ‘whoosh’ sound and flames, demonstrates the large amount of energy released in the combustion of alcohols.
This demonstration requires careful preparation, with strict adherence to the conditions required by the risk assessment provided. Schools are advised not to deviate from the details described in this risk assessment. If any variation is necessary, members should contact CLEAPSS® for a Special Risk Assessment.
A single demonstration will take 5 – 10 minutes. It is recommended that any repeat demonstrations use spare dry reaction vessels. Under no circumstances should the reaction vessel be flushed out with pure oxygen in order to be quickly reused.
Apparatus and chemicals
- Eye protection
- Reaction vessel, 1 or more (see note 1)
- Rubber stopper or plastic cap (to fit the reaction vessel)
- Beaker (250 cm3), 1 for each alcohol used
- Wooden splints, as needed (see note 3)
- Metre rule
- One or more of the following alcohols, 40 cm3 of each one used:
Methanol (Highly flammable, Toxic) Refer to CLEAPSS® Hazcard 40B
Ethanol (IDA, Industrial Denatured Alcohol) (Highly flammable, Harmful) Refer to CLEAPSS® Hazcard 40A
Propan-1-ol (Highly flammable, Irritant) Refer to CLEAPSS® Hazcard 84A
Propan-2-ol (Highly flammable, Irritant) Refer to CLEAPSS® Hazcard 84A
- The reaction vessel consists of a large polycarbonate bottle, as used in workplace water dispensers. These have a volume of 16 - 20 dm3. A clean, dry bottle is required for each demonstration. It takes time to clean and dry once it has been used for a demonstration. For this reason, up to 4 bottles may be required. The bottle must be made of polycarbonate (marked PC) and of no other material. If using empty but wet water cooler containers, stand them inverted to allow any remaining water to drain and then leave upright for several days until completely dry.
- Select a safe, level place for the demonstration, with at least 2.5 m clearance above the top of the vessel to the ceiling above, and no flammable materials above it. If the laboratory bench does not allow for this, 4 stable laboratory stools supporting a large wooden tray may give sufficient clearance and stability.
- Attach a wooden splint to the end of the metre rule or stick using adhesive tape, angling the splint so that when the metre rule is horizontal, the splint is sloping downwards. Provide a lighter or matches well away from the alcohol bottles.
- Set out the bottles containing the alcohols and the beakers at least 1 m away from the demonstration. No flames within 1 m. Students at least 4 m away.
Health & Safety
Both demonstrator and class should be wearing eye protection.
A. Pour about 40 cm3 of the selected alcohol into a beaker and then transfer into the reaction vessel.
B. Insert the rubber stopper and roll the reaction vessel on its side for 10 seconds, to and fro, allowing the alcohol to vaporise and the vapour to fill the vessel. Do not warm the alcohol.
C. Pour surplus liquid alcohol back into the beaker, draining the vessel as completely as possible, and move the beaker back to the rest of the alcohol stock, away from any risk of catching fire. Surplus liquid left in the vessel may ignite and set fire to the vessel as well.
D. Stand the reaction vessel securely inside the safety screens and remove the stopper. Light the wooden splint, and apply the lighted end of the splint to the open neck of the vessel. Do not lean over the screens to apply the ignition. It is dangerous to ignite by dropping a lighted match into the vessel when using ethanol or methanol. For both propanols, this method may be used providing the neck of the bottle is above head height
E. The alcohol vapour should ignite with a loud ‘whoosh’, with flames shooting out of the top of the vessel.
This demonstration is the subject of a Supplementary Risk Assessment by CLEAPSS®, SRA06, which members of CLEAPSS® are able to consult on the Science Publications CD-ROM, updated and re-issued annually to all members. Others will, of course, have to consult their own employer's Risk Assessment.
The experiment demonstrates dramatically just how much chemical energy is released from such a small quantity of fuel.
The flame colour varies with the proportion of carbon in the alcohol molecule. With methanol and ethanol there is a very quick ‘whoosh’ sound and a blue flame shoots out of the bottle. With propan-1-ol and propan-2-ol, the sound is similar but the reaction is slightly slower, easier to observe, and blue and yellow flames may be observed ‘dancing’ in the bottle. The presence of water reduces the likelihood of dancing flames.
This experiment has been reproduced from Practical Chemistry: http://practicalchemistry.org/experiments/the-whoosh-bottle-demonstration,240,EX.html
A wide-ranging and up-to-date review of the production and use of alcohols for vehicle fuels, with links to a variety of related sites, can be found at: http://en.wikipedia.org/wiki/Alcohol_fuel