- Prepare solutions of different indicators.
- Add base (sodium hydroxide solution) to these solutions to change their color.
- Put a piece of dry ice in each solution.
A piece of dry ice put into solutions of different indicators with base, and solutions change color
Scientific name: Dry ice dissolves in the water solution of the indicator with sodium hydroxide and produces carbonic acid which changes pH of the solution
Wear eye protection goggles.
Prevent skin contact with acid and base solutions.
Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.
CO2 + H2O → H2CO3
H2CO3 → H+ + HCO3-
2NaOH + H2CO3 → Na2CO3 + 2H2O
NaOH + H2CO3 → NaHCO3 + H2O
Dry ice consists of carbon dioxide. Because CO2 is a weak acid oxide it produces weak carbonic acid (H2CO3) in the reaction with water.
This acid reacts with sodium hydroxide , in result Na2CO3 and NaHCO3 are formed. While the pH changes the indicator solution gradually changes color in order to the indicator properties.
Thus we can obtain characteristic color transitions:
The universal indicator turns into all the colors of the raonbow;
Phenolphthalein - from pink to colorless at pH range 8.2-10.0;
Thymolphthalein - from blue to colorless at pH range 8.3-10.6;
Thymol blue - from blue to yellow at pH range 8.0-9.6;
Phenol red - from red to yellow at pH range 6.8-8.4;
Bromothymol blue - from blue to yellow at pH range: 6.0-7.6;
Indigo carmine - from blue to yellow at pH range: 11.4-13.0;
You may use other indicators for this experiment.