Ice and Soda

This week's experiment came to me from my good friend Bob Cox. He told me about the trick and wanted to know why it worked. It took some thought and testing to come up with a theory of what is happening and then several e-mails to experts to confirm that I was on the right track.

For this week's experiment, you will need:

  • 2 glasses
  • ice
  • carbonated soda

Use ice cubes that have just come from the freezer. You don't want them to sit at room temperature too long. Put a few cubes into each glass.

For one glass, fill the glass with water and then quickly pour the water out.

Then pour carbonated soda into both glasses. Observe any differences between the two.

What did you observe? The glass where we rinsed the ice with water produced quite a bit less foam than the glass with the drier ice. What is the difference between ice fresh from the freezer and "wet" ice? Comparing the surfaces of the two, the wet ice is much smoother. The fresh ice has a surface with lots of rough spots and irregularities. Why would this make a difference?

The carbonated soda is a liquid with a gas dissolved in it. This gas (carbon dioxide) easily comes out of solution, forming bubbles. Rough surfaces give the gas bubbles a better place to form, producing more foam. You can see this by trying another rough surface, some grains of sugar. When you sprinkle the grains of sugar into the soda, it foams up. If you dissolve the sugar in a little water, you can add the solution without the same level of foam. You could do the same thing with a little salt, but then you would not want to drink the soda afterwards. It would be a shame to let it go to waste. You would not believe how much soda I drank while researching this one. Sometimes we have to make sacrifices in the name of science.