The Chemistry Continues
The Alka-Seltzer Fizz
An Alka-Seltzer tablet contains aspirin, sodium bicarbonate, and citric acid. When placed in
water the sodium bicarbonate and citric acid react with each other to form bubbles of carbon
dioxide gas.
Ask students to predict
 An Alka-Seltzer tablet contains aspirin, sodium bicarbonate, and citric
acid. Based on your experience combining sodium bicarbonate and an
acid, what might happen if we place an Alka-Seltzer tablet in water?
The powders in the tablet will react with each other in water to produce bubbles.
Teacher demonstration
Question to investigate
What will happen when an Alka-Seltzer tablet is placed in water?
Materials
 Alka-Seltzer
 Water
 Graduated cylinder (100 mL)
 Detergent solution
 Dropper
Note
A drop of detergent solution is added to the water so that the bubbles
last longer and are easier for students to see.
Procedure
1. Place 50 mL of water in a 100 mL graduated cylinder.
2. Add 1 drop of detergent solution and swirl gently to mix.
3. Place the graduated cylinder in a waste container.
4. Drop half of an Alka-Seltzer tablet in the graduated cylinder.
Expected results
White foam will rise up in the graduated cylinder and overflow as the tablet becomes smaller
and smaller.
Ask students
 Do you think this is a chemical reaction? Why?
Yes, this is a chemical reaction because a gas was produced. This gas was not in one of
the reactants, so it must have been produced during the chemical reaction.
 Why do you think this reaction is similar to the reaction of vinegar and baking soda?
Citric acid and vinegar are both acids and interact with sodium bicarbonate in a similar
way to produce carbon dioxide gas.
Think about it
Baking soda in water does not bubble but baking powder in water does bubble. Baking powder
contains baking soda and something else that makes it bubble. What do you think that
something else might be?
Chemistry explanation
Alka-Seltzer tablets and baking powder both contain sodium bicarbonate and a powdered acid.
Alka-Seltzer tablets contain two acids, aspirin and citric acid. Baking powder may contain an
acid like cream of tartar, calcium acid phosphate, or some other acid. When either of these
products is placed in water, the acid and sodium bicarbonate react to produce carbon dioxide
gas.