Ask A Scientist General Science Archive

name         Adam G.
status       student
age          12

Question -   If you have three glasses two glass glasses and a plastic
one and you take a can of pop, pour it into the first glass tumbler and
after it sits there are no bubbles in it then you put pop into the
plastic tumbler and there are all kinds of bubbles sticking to the side
and to the bottom and then you put some pop into the second glass
tumbler and there are bubbles in the second glass   tumbler.  What makes this
happen?
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Carbonated beverages are supersaturated solutions of CO2. How fast the CO2
bubbles out to achieve equilibrium depends upon the type and number of
seeding sites that are present. In the case of the plastic glass, small,
even microscopic, scratches on the walls provide excellent sites for bubble
growth. You can also see the effect by throwing in a pinch of salt, which
will usually cause the rapid escape of the CO2. That there is glass-to-glass
differences is not surprising. Even a small residue of soap, or soap scum
can have a big effect.

Vince Calder
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