Kids, what causes the “smoke” from bubbling beakers and flasks in TV shows and movies? Dry ice is another name for the solid form of carbon dioxide (CO2). It is colder than water ice but can be handled safely for short periods of time with insulating gloves. There is a video of the classic dry ice fog demonstration on-line (at http://www.metacafe.com/watch/286601/dry_ice/ ), with a twist. After water is added to the dry ice to create a smoky fog, hand soap is squirted into the mix. The resulting cascade of bubbles is fun, but what makes this video really interesting is the bubbles vanishing in a puff of fog when touched.
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
To try this at home, we recommend an adult partner only for handling the dry ice, using tongs and insulating gloves (such as leather gardening gloves). A double Styrofoam cup makes a good container, and we suggest putting this inside a secondary container (like a dishpan, for example). A ceramic coffee cup would probably also work. A single large chunk of dry ice will last longer than a number of smaller chunks, and hot water works better than cold, but just use hot water from the tap. Boiling hot water could create a hazard in handling.
Dry ice is so called because it does not melt into liquid carbon dioxide before turning into gas. The process of a liquid changing state into gas is called evaporation. When a solid changes directly into gas, the process is called sublimation.
The white cloud that forms is not smoke, but rather condensed water vapor. Tiny droplets of water make the white cloud. The clouds almost immediately disappear because the water droplets warm right back up and re-evaporate back to form invisible water vapor. This is how fog forms: when it is humid enough and the temperature drops enough you get lots of tiny water droplets forming.
Notes
Your adult partner can get dry ice from a specialty gas company, such as one that deals in oxygen, helium, and nitrogen, or from stores that ship perishable food. Bakeries and seafood shops can often provide a good lead, or a popular restaurant could be asked if they carry dry ice. Dry ice is cold enough to cause frostbite so protective gloves are necessary. Also, be aware that extra carbon dioxide is added to the air as dry ice vaporizes. Carbon dioxide is naturally present in air, but under some circumstances, the extra amount can present a health hazard.
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
January 2007
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Reference:
Dr. Anne Marie Helmenstine at
http://chemistry.about.com/library/weekly/aa010603a.htm
http://chemistry.about.com/b/a/257641.htm
http://chemistry.about.com/cs/howtos/ht/nontoxicsmoke.htm
