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Acidity Change of Dry Ice in Water


1 Liter graduated Cylinder

Fisher Universal Indicator

Color Comparison Chart for Overhead Projector for The Universal Indicator

Dry Ice Chunks

DI Water

3M Sodium Hydroxide

Thermal Gloves

Gloves and Goggles



  1. Add a few mLs of universal indicator to 900mL of water in a 1 liter graduated cylinder. Color is red from dissolved CO2 in the water.
  2. Use the Color Comparision Chart to  show the pH of the water.
  3. Drop in a chunk of dry ice.
  4. Add 5mLs of 3M NaOH. Color changes from purple to yellow as the pH drops. pH never gets low enough again to turn indicator red. Repeat cycle.
  5. Reaction slows down with successive aliquots of NaOH showing the buffering effects of the salts formed.



CO2(s) --> CO2(g)

CO2(g) + H2O --> H2CO3 <--> H+ + HCO3-(aq)

2NaOH (aq) + CO2(g) --> Na2CO3(aq) + H2O


Waste Management

The solution can be neutralized and poured down the sink.