For this experiment you
will need:
- a can of colorless soda (e.g., 7-Up or Sprite)
- a tall, clear glass or plastic cup
- several raisins (fresh raisins work the best)
Pour the can of soda
into the tall glass. Notice the bubbles coming up from the bottom of the glass.
The bubbles are carbon dioxide gas released from the liquid.
Drop 6 or 7 raisins into
the glass. Watch the raisins for a few seconds. Describe what is happening to
the raisins. Do they sink or float? Keep watching; what happens in the next
several minutes?
Raisins are denser than
the liquid in the soda, so initially they sink to the bottom of the glass. The
carbonated soft drink releases carbon dioxide bubbles. When these bubbles stick
to the rough surface of a raisin, the raisin is lifted because of the increase
in buoyancy. When the raisin reaches the surface, the bubbles pop, and the
carbon dioxide gas escapes into the air. This causes the raisin to lose
buoyancy and sink. This rising and sinking of the raisins continues until most
of the carbon dioxide has escaped, and the soda goes flat. Furthermore, with
time the raisin gets soggy and becomes too heavy to rise to the surface.
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