The sealed bag fills with gas. The carbon dioxide is acidic and changes the color of the phenol red from red to yellow. Students can vary the relative amounts of the chemicals, and select different chemicals on which to place the added liquid inside the sealed sack. Go to Top Makeup Ans. Two reactants are mixed inside a plastic bag.
Phenol red is added as an indicator.
The color changes and gas bubbles are observed with all three components are mixed. The indicator is first added to the CaCl 2 resulting in a red solution. The red solution is then added to the NaHCO 3 resulting in a change to yellow. Bubbles are also evolved. Gas is produced in the bag.