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DemonstrationsAcids, Bases, Buffers, Titrations › 16.3

Lecture Demonstrations

Acids, Bases, Buffers, Titrations

16.3 Acid Breath

Subjects: Acids/bases, titrations

Description: The instructor breathes into a flask containing a colored solution. After several breaths, the color of the solution will change.


  • 250 mL Erlenmeyer flask with stopper to fit
  • Disposable pipets
  • ~50 mL water
  • ~10 drops Universal indicator solution‡
  • Saturated sodium bicarbonate (if needed)‡

Saturated bicarbonate solution is located on the solutions shelf. Universal indicator is located in the flammables cabinet.

Pre-class preparation:

1. Add water and the Universal indicator to the flask.
2. Add 1 drop of saturated sodium bicarbonate solution to produce a slightly basic solution blue/green in color.
3. Stopper the flask until you’re ready to perform the demo.


1. Unstopper the flask.
2. Breathe into the flask several times. Swirl the flask between breaths.
3. The solution will turn orange/yellow after approximately 10 breaths due to a decrease in pH.


After several breaths, there will be enough CO2 dissolved in the solution to produce enough carbonic acid to cause a decrease in the pH of the solution. The equation for the reaction is given below. The decrease in pH produces a color change of the indicator.

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




Solutions can be flushed down the drain with water.


1. L. Summerlin; C. Borgford; J. Ealy. Chemical Demonstrations: A Sourcebook for Teachers; Volume 1; 1985; p. 40

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