November 2012

# Sharing chemistry with the community

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Natalie Miller*, Duke University, Durham NC

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## “Miniature Whoosh Bottle Demonstration”

The “Whoosh Bottle” demonstration has proven to be very popular with audiences of all ages. A small amount of alcohol is placed in a plastic bottle, which is then capped and shaken to allow the alcohol to evaporate and mix with the air. The cap is removed and the mixture is ignited. The demonstration gets its name from the sound made as the hot, expanding gases escape through the mouth of the bottle while cooler air enters. Because the demonstration is quite versatile, it can be performed for a wide range of audiences. The underlying chemical concepts include the principles of combustion, thermodynamics and kinetics. Relevance can be established through a discussion of alcohol as an alternative fuel.

## Concepts

- Combustion of alcohols
- Products of combustion of alcohols
- Exothermic processes
- Enthalpy
- Alternative fuels

## Materials

- 2-L clear, colorless, plastic soda bottles with lids (thoroughly rinsed and dried)
- Ring stand and ring clamp (to hold soda bottle securely in an upright position)
- Ethanol or isopropanol (~ 5 mL per demonstration; I put some alcohol in a small bottle for ease of dispensing and to limit the fire hazard)
- Dropping pipette
- Long stem fireplace matches or candle secured on a long pole
- Freshly prepared limewater (calcium hydroxide solution)
- One-hole rubber stopper fitted with a short piece of glass tubing that has about a one-foot long piece of Tygon® tubing attached

## Safety

- Wear safety glasses; long hair should be tied back
- Do not use glass bottles. When plastic bottle begins to show crazing, frosting and cracking, use new bottle.
- Fire hazard exists; be sure all flammable materials are removed from the area prior to ignition of the alcohol in the soda bottle. Ensure the ethanol bottle is sealed and removed.
- Fire shoots up and out of the mouth of the bottle; ignite the mixture at arm’s length; keep your face and other parts of your body away from the mouth of the bottle when igniting.
- Keep audience at least 8 feet away from the demonstration and/or use a safety shield.
- Do not ADD oxygen to the soda bottle; explosion could occur.

## Advanced preparation

Secure the soda bottle to the ring stand by lowering the ring over the neck of the bottle. You want the ring to be at a height that the bottle is in place, yet you can still remove and reinsert the bottle without having to change the position of the ring.

Fresh limewater can be prepared by adding a teaspoon of calcium hydroxide to about 100 mL of water, stir, let stand for about five minutes, and filter, collecting the filtrate in a flask. Stopper the flask tightly to prevent carbon dioxide in the air from reacting with it.

## Procedure

1. Transfer (two dropping pipettes full) alcohol into the 2-L soda bottle and then cap the soda bottle. Cap the bottle of alcohol and it move away from the area.
2. Swirl the soda bottle to aid in the evaporation and dispersion of the alcohol.
3. Secure the bottle to the ring stand.
4. When ready to ignite the alcohol, remove the cap, light the fireplace match, and at arm’s length hold the flame just inside the top of the soda bottle.
5. After the fire goes out you can remove the bottle and take it around to the audience allowing them to feel how warm the bottle has become; burning is an exothermic process.
6. One can also see the fog forming as a result of the water vapor condensing as the bottle cools; water is one of the products of combustion; point this out to the audience.
7. To show that carbon dioxide was also formed during the combustion of the alcohol, fit the bottle with the one-hole stopper assembly. Place the end of the Tygon® tubing into the container of limewater and gently squeeze the bottle. A white cloudy precipitate forms (calcium carbonate) as a result of the carbon dioxide reacting with the calcium hydroxide. Be sure to remove the hose before letting go of the bottle or the limewater will be drawn into the soda bottle.

## Disposal

- Rinse the soda bottle and place it in a recycling bin.
- Limewater can safely be disposed of in the sink.

Be sure the used match is extinguished before placing it in the trash.

## Discussion

There are several advantages to this downscaled version that uses a colorless 2-liter plastic soda bottle in place of a blue
5-gallon water bottle. It is easier to transport, uses less alcohol, is safer, can be readily repeated, and allows for greater audience participation. Natalie Miller performed this demonstration at a recent chemistry outreach event. The following are her reflections on learning and performing the demonstration:

This demonstration was one of several demonstrations that two other volunteers and I performed for twenty-eight girls participating in the Duke Action Camp for MS Girls. The theme for the presentation was “Chemical Energy”. I found learning the basic mechanics of the demonstration to be relatively easy. During practice I spoke with Dr. Lyle about where in the sequence I would perform the demonstration and the points to be stressed. We also talked about the age and background of the audience. I used this information in planning my “talk”. This particular demonstration definitely has that “wow” factor that engages the audience. Engaging the audience and maintaining their engagement throughout the presentation is important for fostering understanding of the chemical concepts. I’ve learned a number of techniques that have proven to be effective, including the use of humor, which I incorporated into my presentation.

I began by asking the girls to identify the three required components for combustion to occur so I could assess their current understanding. Seeing that they did understand, I then proceeded with performing the demonstration, informing the audience of what I was doing step-by-step. When mixing the alcohol with the air in the bottle I did a “shake ‘em up dance” and invited the girls to join me. They did so enthusiastically!

Before igniting the alcohol I asked them to identify the fuel, the source of oxygen, and what else was needed. I then brought out the missing source of ignition (a match), lit it, warned them to cover their ears, and ignited the alcohol. I was truly amazed to see the wide-eyed expressions of wonderment on the girls’ faces and to hear their “Oohs! Aahs! and Wows!” especially since they had already observed several instances of fire, pops, and bangs prior to this demonstration. I then removed the bottle from the ring stand and carried it around allowing each girl to feel the warmth of the bottle, introducing the term exothermic as I did. When the fog inside the bottle began to form I asked the girls what they saw. They responded with a variety of answers including, “Fog! Smoke! Steam!” I stressed that what they were seeing was a fog or mist that formed as the bottle cools. Water was produced in the combustion reaction but we could not see it at first because the water was in the gas phase. As the tempera-ture inside the bottle dropped the gaseous water condensed into liquid water, becoming visible. Based on the girls’ verbal and nonverbal responses, I believe my presentation was successful.

My favorite part of performing this demonstration and participating in chemistry outreach in general is the interaction with the audience and watching the changes in their facial expressions as the presentation progresses — the joy as they danced along with me as I dispersed the alcohol in the bottle; their furrowed brows as they pondered the principles of com-bustion; their apprehension in anticipation of what will happen when the alcohol is ignited; the “wow” as they observed what happened; the enthusiasm as I carried the bottle around for them to feel the heat that was generated; and their smiles of confidence as they appeared to understand what happened and why.

*Natalie Miller is a junior at Duke University majoring in biology with a minor in chemistry. She plans to pursue a career in medicine upon graduation.

**Dr. Kenneth Lyle, a lecturing-fellow in the Department of Chemistry at Duke University, serves as the lecture-demonstrator, chemistry outreach coordinator, and instructor of CHEM 180 Chemistry Outreach Service Learning Course. All inquires should be addressed to kenneth.lyle@duke.edu.

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