What is the purpose of alka seltzer?

It bubbles, creating pressure in a soda bottle. It doesn't create enough pressure to break the bottle, but if the bottle is thrown afterwards it will break the cap and create a small explosion of soda. This takes a lot of Alka-Seltzer® and not much happens. Don't waste your time. No different than shaking a soda can and then throwing it, except it takes more work and money.