Grades 3–5 · Everyday Life
Why do fizzy drinks release bubbles?
A fizzy drink contains carbon dioxide mixed into its water. Much of this gas is dissolved, so it is spread through the liquid rather than collected in visible bubbles. The sealed container holds carbon dioxide above the drink at a higher pressure than it will have after opening.
In the diagramOpening a fizzy drink lets dissolved gas escapeSealedAfter openingHigher gas pressureLower gas pressureGas leavesOpenTiny roughsites helpbubbles startDissolved gas gathers into growing bubbles.Gas amounts and bubble sizes are schematic.
Opening lets gas above the liquid escape and lowers that pressure. Under these new conditions, some dissolved carbon dioxide leaves the water. Tiny rough places on the container or other surfaces help bubbles begin. Gas molecules gather there, and a bubble can grow before breaking away.
The bubbles carry carbon dioxide out of the drink and into the air. As the drink loses dissolved gas, it becomes less fizzy. Opening has allowed gas already in the drink to leave; it has not created a fresh supply of gas. Even before the first bubble appeared, the dissolved gas was already mixed through the water.
About this explanation
Starting knowledge: Know that gases can mix with liquids even when bubbles are not visible.
Sources
- American Chemical Society — Unleashing Carbon Dioxide
- American Chemical Society — The Secret Science of Soda Pop