Visual Evidence:
* Fizzing and Bubbling: The most obvious sign! The tablet rapidly releases carbon dioxide gas, creating bubbles that rise to the surface.
* Dissolving: The tablet gradually disappears as it breaks down and dissolves in the water.
* Change in Temperature: The reaction is slightly endothermic, meaning it absorbs a small amount of heat from the surroundings. You might notice a slight cooling effect in the water.
Other Evidence:
* Production of a Gas: You can actually feel the gas being released by holding your hand over the glass.
* Change in pH: Alka-Seltzer is basic (alkaline) due to the presence of sodium bicarbonate. The reaction with water releases carbon dioxide, which is acidic. The pH of the solution would change.
Explanation:
Alka-Seltzer tablets contain sodium bicarbonate (baking soda), citric acid, and aspirin. When dropped into water, the citric acid reacts with the sodium bicarbonate to produce carbon dioxide gas:
* NaHCO₃ (sodium bicarbonate) + H₃C₆H₅O₇ (citric acid) → CO₂ (carbon dioxide) + H₂O (water) + Na₃C₆H₅O₇ (sodium citrate)
This reaction is what causes the fizzing and bubbling you see. The aspirin is simply a pain reliever that dissolves in the water.
