Dry Ice pH Colour Change

Adding dry ice to a beaker of water with universal indicator creates bubbling fog and a color change. As carbon dioxide dissolves into the water, the solution becomes acidic and shifts from green through the color spectrum to orange. Adding base resets the cycle.

1. Fill a beaker or container with water and add several drops of universal indicator.
2. Using gloves or tongs, add chunks of dry ice.
3. Watch as the solution bubbles, fog forms, and the color changes from green to orange as carbonic acid forms.

• Add a small amount of 0.1 M sodium hydroxide (NaOH) before starting to make the initial colour of the universal indicator purple.
• Add more concentrated sodium hydroxide once finished to get the solution back to a purple colour.
• Use different acid–base indicators to observe alternate color changes.

• Always wear gloves or use tongs when handling dry ice to avoid frostbite.
• Wear goggles and a lab coat when working with strong bases (sodium hydroxide).
• Use only small amounts of concentrated sodium hydroxide and handle with care - it is corrosive.
• Conduct in a ventilated space, since sublimating dry ice releases carbon dioxide gas.
• Keep dry ice and sodium hydroxide away from children and pets.

• Why does dissolving carbon dioxide make the water acidic?
• How does the universal indicator show the gradual change in pH?
• Why does the fog flow over the edge of the beaker instead of rising?
• How does adding NaOH reset the solution back to purple?