Make Your Own Alka Seltzer Tablets #Chemistry The fizzing of Alka-Seltzer tablets is due to a chemical reaction between citric acid and sodium bicarbonate (baking soda) in the tablet when it dissolves in water. When these two substances mix with water, they react to form sodium citrate, water, and carbon dioxide gas. The carbon dioxide gas is what creates the characteristic fizzing bubbles. This reaction is similar to the classic "baking soda and vinegar" experiment, where the release of carbon