If you pour soda pop into a glass at room temperature is fizzes, but if you pour it into ice it fizzes a lot. Though carbon dioxide is more soluble in the pop at low temperature, why does it fizz more with the ice?
It isn't the coldness, but the surface of the ice cube itself that creates the fizz.
Bubbles form more easily on rough surfaces than smooth ones. If you have a pan with tiny
scratches on its inside bottom, try putting it on a burner with some water in it. Just
as it starts to show signs of boiling, you'll notice the first bubbles form along those
scratch marks. These areas are called 'cavitation sites'.
An ice cube dropped into a sparkling beverage generates bubbles NOT because of its
but because its surface roughness provides more cavitation sites.
Paul Walorski, B.A., Part-Time Physics Instructor
The extra fizz in a glass full of ice is due to a 'seeding effect.' Although you are
correct that the solubility of CO2 is higher in colder soda, The formation of visible
bubbles is also dependent on the collection of gas molecules together. Due to the
polarity of water and the non-polar nature of CO2 molecules, any nascent bubble will
quickly enlarge as nearby molecules collide and merge with it. The gas molecules are far
less likely to return to the polar aqueous environment surrounding the bubble, as the
attraction between water molecule squeezes the CO2 out from between the water molecules.
So if you can get a bubble started, it will grow to visible size and float to the top.
The ice provides a substrate with small crystalline holes which can temporarily hold a few
CO2 molecules near each other and get the ball rolling. You can see the same effect if
you pour your soda into a glass with a scratch on the inside, and a similar effect if you
just use a dirty glass (try rubbing your finger up one side before pouring).
This effect is noticeable only because the solubility of CO2 is so low in water in the
first place. The random collisions of particles at refrigerator cold temperatures is low
enough to allow many distant CO2 molecules to remain isolated for a long time (many
minutes) without a little help from some surface.
Rob Landolfi, None, Science Teacher, Washington, DC
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