text: This experiment demonstrates the properties of acids, bases, pH indicators, and the properties of carbon dioxide. First, a large amount of universal indicator is added to water to facilitate the visual detection of changes in the solution's pH. Then, a few drops of ammonia (NH) or sodium hydroxide (NaOH) is mixed into the solution, which changes the color of the solution; the type of pH indicator used determines which colors are seen. Dry ice is subsequently added to form carbonic acid, changing the pH of the solution from basic to acidic.  This causes the solution to change colors again. Simultaneously, a cloud of carbon dioxide is generated from the sublimation of dry ice due to the condensation of water vapor in the air.