Question

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?

Asked by: Bob Snyder

Answer

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 temperature, but because its surface roughness provides more cavitation sites.

Answered by: 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.

Answered by: Rob Landolfi, None, Science Teacher, Washington, DC

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