Reaction #7 - Alka-Seltzer tablet

I'm sure all of you have heard about the effervescence of an Alka-Seltzer tablet (an antacid) when it is placed in water. But do you know how it works?

Well, here is the answer: The Alka-Seltzer tablet contains sodium bicarbonate (and a little bit of potassium bicarbonate) and anhydrous citric acid. In solid forms, the chemicals do not react. But once they are dissolved, they react vigorously:

C₆H₈O₇ (aq) + 3 NaHCO₃ (aq) → Na₃C₆H₅O₇ (aq) + 3 H₂O (l) + 3 CO₂ (g)
Citric acid + Sodium bicarbonate → Sodium citrate + Water + Carbon dioxide

Thus, the carbon dioxide gas bubbles out of the solution.

Reaction by YOSF