Here is a video from the International Space Station of an Alka-Seltzer tablet being put in to a sphere of water in zeroG.
Here is an interesting little side experiment from the International Space Station where and Alka-Seltzer tablet is put in to a sphere of water in zeroG. The results are actually some what surprising. The bubbles collect in the water sphere even coalescing into untimely two big ones.
It would be fun to see this with Menthos candy and a sphere of Diet Coke. Given what Menthos in a bottle of Diet Coke does on Earth, I would recommend not trying this suggestion near any sensitive equipment. Inside an empty progress vehicle would probably be best.
Now before any one goes writing their congress men about the waste tax payer dollars, note that this in not their mission. This is the type of thing astronauts do to have a little fun after a long hard day of the real work.