Summary
Solid carbon dioxide is added to a large beaker of water containing universal indicator. As the CO₂ dissolves, the indicator changes from neutral (green) to acidic (orange).
Hazards
Dry Ice is extremely cold, use gloves or tongs when handling.
Chemicals and Solutions
- Universal indicator solution
- 2 lbs. dry ice
- 25 mL of 0.l M NaOH solution
- 6 M NaOH solution
Materials
4 liter beaker of water
Procedure
Add univeral indicator solution to the water and make the solution purple by adding some 0.1 M NaOH solution. Then just start adding dry ice to the solution. The dry ice will sublime causing the solution to bubble and it will also dissolve in the water forming carbonic acid causing the indicator to change colors as the solution becomes more and more acidic. The solution will change from purple to blue to green to yellow to orange and finally to red. Once the red color is reached 6M NaOH can be added to take the color back up to purple and the cycle can begin again.