Chemical Concepts Demonstrated

• Chemistry of HCO₃^- ion
• Acid-base reactions
• LeChatelier's Principle

Demonstration

Three balloons are attached to three bottles as shown in the picture. All of the balloons contain Alka-Seltzer. The first bottle contains 250 ml of water. The second bottle contains 250 ml of water and 3 ml of HCl. The third bottle contains 100 ml of water and 150 ml of a soft drink.

Drop the alka-seltzer into the bottles.

Observations

The more acidic the solution, the larger the amount of CO₂ gas is produced.   These amounts can easily be measured by comparing the resulting size of the balloons.  The plain water produces the least amount of gas, the water and hydrochloric acid produces a moderate amount, and the water and soft drink produce the most gas.

Explanation (including important chemical equations)

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

HCl is a stronger acid than water.  Larger amounts of acid will increase the acidity of the solution and push the reaction towards the production of products (i.e. more acidity yields more CO₂ gas).

Contributors

• Dr. George Bodner (Perdue University)

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