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This week's LabZone activity
Oct. 26, 2005
Original Bubble Chamber
Watch table salt streak like a comet's tail and explore solubility, ionization, and subatomic particles.
Description:
A carbonated beverage and salt crystals demonstrate how invisible particles can be detected.
You Will Need:
- carbonated soft drink
- tall, transparent vessel
- table salt
- tweezers
Instructions:
Make certain the tall glass vessel is immaculately clean.
A 500 ml graduated cylinder works well for this activity. A funnel-shaped glass works even better.
Fill the glass container with soft drink. To keep foaming at a minimum, pour the beverage very slowly down the side of the tilted vessel.
Allow the glass of beverage to remain undisturbed for several minutes. Wait until most of the surface foam has dissipated.
Carefully drop a single grain of salt into the beverage. Make note of the trail of bubbles released as the salt grain falls through the liquid.
Content:
Common salt is made of sodium chloride. As a grain of salt falls through the liquid, it begins to dissolve. The dissolving process causes the molecules of sodium chloride to break apart, not into atoms of sodium and chlorine, but ions; a positively charged sodium ion and a negatively charged chloride ion. The sodium atom releases one electron that is captured by the chlorine atom.
Carbonated drinks contain a gas in solution, carbon dioxide. Molecules of carbon dioxide are attracted to the charged ions. Molecules of carbon dioxide gather around the ions and form a bubble.
The ions are too small to be seen. The bubbles of gas that gather around them are visible.
One of the legends of atomic science features two scientists relaxing and discussing their work. One of the scientists was restlessly fidgeting with items on the table as he talked with his friend. He picked up a grain of salt from the tabletop and dropped it in a half-empty glass of soda. He noticed a trail of bubbles following the path of the descending salt grain. He repeated the activity with smaller and smaller bits of salt. Finally, he dropped in a very tiny bit so small that he could not see it fall through the liquid. Yet, the invisible salt created a bubble trail. Scientists used that discovery as the basis for a famous piece of scientific equipment: the bubble chamber. For many years, scientists used bubble chambers to detect the presence of ions and subatomic particles.
Streams of subatomic particles are shot through a special liquid. The paths of the particles are made evident by trails of tiny bubbles. Photographic analyses of those tiny bubble trails allow scientists to determine mass, charge, and other characteristics.
Teacher's Notes
Activity excerpted by permission of the Chemical Educational Foundation (www.chemed.org) from You Be The Chemist. For additional information about these activities and lesson plans, see www.chemed.org/Kit.html.
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