In this demonstration, learners observe vinegar and baking soda reacting to form carbon dioxide (CO2) gas. The CO2 gas is trapped in a balloon, then blown through a straw into water with an acid-base indicator. The indicator changes to indicate that CO2 mixed with water becomes an acid. This demonstration is part of a set of demonstrations and activities that can be used together for a larger lesson. Resource contains vocabulary definitions and suggestions for assessment, extensions, and scaling for different levels of learners.