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Activity

Antacid molecules

Summary: 
Crushed antacid tablets remove H atoms from fake stomach juice, to show how antacids work.
Science content (2016 curriculum): 
Chemistry: Atoms, Molecules (3-7)
Chemistry: Chemical Changes (2, 7)
Science topic (2005 curriculum connection): 
Life Science: Human Body (grade 5)
Physical Science: Chemistry (grade 7)
Materials: 
  • Bottle of antacid (the tablets should be broken into smaller pieces)
  • Mortar and pestle
  • Dropper bottle with fake stomach juice = (0.01M HCl, or use vinegar)
  • Round wooden sticks in plastic container
  • Dropper bottle with dye that can distinguish between pH 2 and 7 e.g. red cabbage juice, or commercial pH indicator
  • Plastic cups
Procedure: 

Put 10 drops of fake stomach juice into each of two cups. Stomach juice contains loose hydrogen atoms.
Add a drop of dye to both cups of fake stomach juice. The color of the dye shows you the number of loose hydrogen atoms in the stomach juice.
How many hydrogen atoms are there in stomach juice?

Real stomach juice, like the fake stomach juice in your experiment, has lots of loose hydrogen atoms in it. Your stomach uses the loose hydrogen atoms to digest food. But sometimes stomach juice spills into the tube above the stomach. Hydrogen atoms are not meant to be in the tube above the stomach, and cause a burning feeling. This pain is called heartburn. When we get heartburn, we take an antacid.

Take a small piece of antacid and grind into a powder with the mortar and pestle. Dip a wooden stick into one of your cups of stomach juice to make it wet. Pick up some of the antacid powder with the wet stick. You only need a small amount.

Mix the antacid powder into one of your cups of stomach juice and dye. Leave the other cup alone. Keep mixing until the stomach juice changes color. Be patient — it may take a minute. Compare your two cups. What did the antacid do to the number of hydrogen atoms in the stomach juice? (Look at what colour the dye turned and infer what has happened to the number of hydrogen atoms).

How did the antacid take away the hydrogen atoms?
The antacid contains carbonate molecules. Find carbonate in the active ingredients on the antacid bottle. The carbonate molecules capture the loose hydrogen atoms to make a different molecule. (Students can build the molecules to see the reaction: CO3 + 2H -> CO(OH)2

How do antacids get rid of heartburn?
Just like in your experiment, the carbonate molecules in the antacid capture the loose hydrogen atoms in your stomach tube and the burning pain of heartburn goes away.
antacid = "anti-acid": Antacids get their name because they remove (or neutralize) acid, which is the same as removing hydrogen atoms.

Attached documents: 
Notes: 

Tested with family groups of adults and children of all ages.

Grades tested: 
Gr K
Gr 1
Gr 2
Gr 3
Gr 4
Gr 5
Gr 6
Gr 7
Teacher: 
Self guided
Teaching site: 
New York Hall of Science