Sewell's Science

Alka-Seltzer tablets contain a powdered acid and base (acid: citric acid, base: sodium hydrogen carbonate). They do not react with each other as they are in the solid state. However when they are dissolved in water to form a solution, they do react.

The reaction produces Carbon Dioxide (CO2). This can be seen as fizzing (Effervescence).

If this reaction is trapped in something then the pressure will build up until the container cannot take any more and the lid pops off.

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