So if you want to know what’s going on in this, here’s the details. Alka-Seltzer tablets are essentially a solid mix of two components; citric acid and sodium bicarbonate. In the solid state, they aren’t able to react with one another, but as soon as water is added, they dissolve and react to form carbon dioxide, water, and sodium citrate. This is a buffer (a solution that resists changes in pH), which is why drinking Alka-Seltzer can help to settle your stomach. In this case, I use the reaction to inflate the bottle with carbon dioxide and to displace the air that was inside. To get the bottle to collapse, I used a solution of sodium hydroxide, which I made by dissolving some household solid drain cleaner (lye) into water. The sodium hydroxide reacts with carbon dioxide in the air, and since the bottle is essentially filled only with carbon dioxide, it collapses in on itself as the gas is consumed by the reaction. The primary product of this reaction is sodium carbonate, which dissolv...