Dry Ice in Universal Indicator
DESCRIPTION:
Universal indicator ranges from red (pH 4) to purple (pH10) as the pH of a substance
changes. Adding NaOH to water starts the solution off as purple. When dry ice is added
to water, some of it forms carbonic acid, and lowers the pH. This is why the solution
changes from purple to blue to green to yellow.
CO2 (s) + H2O (l) → H2CO3 (aq)
At the same time, the dry ice is subliming to gaseous carbon dioxide. The “fog” that we
see is condensed water vapor though, not carbon dioxide.
TOPICS COVERED:
- acids and bases
- indicators
- cryogenics
- sublimation
- color change
- chemical change
- condensation
- physical change
MATERIALS NEEDED:
- universal indicator
- large flask (any other glass container will work)
- dry ice
- dilute NaOH solution
PROCEDURE:
1. Fill the flask ~3/4 full of the dilute NaOH solution
2. Add a few mL of universal indicator
3. Add dry ice
ADDITIONAL COMMENTS:
A solution that has 1 pellet of NaOH per 1000mL of water works well.
SAFETY:
Universal indicator can stain, dry ice can cause severe burns, goggles should be worn
at all times, and caution should be taken.
REFERENCES:
"Dry Ice "Titration"." Chemistry Demos. Chemistry @ Indiana University, 07 Jun 2011.
http://sites.jmu.edu/chemdemo
JMU Department of Chemistry and Biochemistry
Accessed 14 Jun 2010. <http://outreach.chem.indiana.edu/demos/5-4 Dry Ice
Titration.doc>.
Foster, Laurence S.; Gruntfest, Irving J. Demonstration Experiments Using Universal
Indicators. J. Chem. Educ. 1937, 14 (6), 247.
STORY:
You can talk about how more carbon dioxide in our atmosphere effects the pH of
aqueous environments, and how soda is so acidic because carbon dioxide is
pressurized into it.
http://sites.jmu.edu/chemdemo
JMU Department of Chemistry and Biochemistry