E755 - Acid/Base - Universal Indicator and Dry Ice
When dry ice is added to a graduated cylinder containing blue liquid (basic water with universal indicator), the dry ice produces bubbles and fog and turns the solution yellow.
TO CONDUCT DEMONSTRATION:
1. Drop dry ice chunks into a graduated cylinder filled with a basic solution and universal indicator.
2. Ask students to make as many observations as possible.
EQUATIONS:
CO2 produces H+ in solution and neutralizes OH-.
CO2(aq) + H2O(l) —> H2CO3(aq) + 2H+(aq) + CO32-(aq)
H+(aq) + OH-(aq) —> H2O(l)
SAFETY AND DISPOSAL:
Eye protection should be worn to avoid splashing base into the eyes.
PRIOR TO LECTURE:
1. Dissolve 6.5g KOH (potassium hydroxide) in 1600mL water and add several drops of universal indicator. Place in 2000mL graduated cylinder.
2. Assemble the following:
a. dry ice in 2" chunks
b. tongs or heat-protective gloves
c. goggles
REFERENCE:
L.R. Summerlin and J.L. Ealy Jr., Chemical Demonstrations: A Sourcebook for Teachers, 1985.
ACKNOWLEDGMENT:
Patrick McKeown, Summer 1989.