Have you been told not to drink pop or soda because it contains too much sugar and is bad for your teeth? Let’s do an experiment to explore this advice!

Materials

• Aluminum foil or plastic wrap
• Cups or glasses, 4
• Eggs, 4
• Measuring spoon
• Paper towel
• Pop or soda
• Sugar
• Toothpaste containing fluoride
• Vinegar, 2 cups
• Optional: Coffee, milk, orange juice, sports drink, tea

Be Safe

Vinegar will irritate eyes and skin. Keep out of your eyes and wear protective glasses and gloves if possible.

Experiment

Prepare a sugar solution by dissolving 2 ¼ tablespoons of sugar in one cup of water. (A 12-oz can of Coke® has about 40 grams of sugar, equivalent to 2 ¼ tablespoons per cup.) Obtain four cups or glasses and pour one cup of vinegar into two of the cups. Pour a cup of soda or pop of your choice into the third cup, and one cup of sugar solution into the fourth cup. Spread a thin layer of fluoridated toothpaste all over ONE of the eggs and place this egg into one of the vinegar solutions. Add one uncoated egg to each of the other three containers. Observe: do you notice any immediate changes in any of the cups?

Cover the containers with aluminum foil or plastic wrap and allow the eggs and liquids to sit undisturbed for a few days. After 2 - 3 days, remove the eggs from the containers and discard the liquids. Place the eggs on a labeled paper towel so you know which egg was in each liquid. Compare any differences in the thickness, color, and appearance of the eggs.

What’s happening?

Eggshells, which are made out of calcium carbonate (CaCO₃), serve as a model for our teeth in this experiment. Teeth are composed of a mineral called hydroxyapatite, or calcium hydroxyphosphate [Ca₅(PO₄)₃OH]. The eggs are thus similar to, but not exactly the same, as our teeth. When you brush your teeth with fluoridated toothpaste, fluoride ions in the toothpaste displace hydroxy (OH) groups in your tooth enamel, making it harder and less reactive. A similar substitution takes place with calcium carbonate in eggshells. Did toothpaste help protect the eggshell?

Did you observe any other changes to the eggs or in the liquids? Eggs placed in vinegar and pop or soda will usually produce bubbles in the liquid. The bubbles are carbon dioxide (CO₂) gas, which forms when acids in vinegar and in pop or soda react with the calcium carbonate in eggshells. This reaction degrades or “eats away” at the eggshell, making eggs placed in those liquids appear noticeably thinner.

What about the egg placed in sugar water? Sugar water is used as a model for pop or soda in this experiment. Compare the appearance of the eggshells for eggs placed in pop versus in sugar water. Sugar does not appear to be the “culprit” in why pop or soda may be bad for your teeth. Sugar alone may not degrade tooth enamel like the acid content in pop or soda does. It is known, however, that sugar helps to “feed” bacteria living in your mouth, and these bacteria in turn produce acids that DO degrade tooth enamel. So pop delivers a “double whammy” due to both the acid AND the sugar that it contains!

Extension 

Experiment with other beverages. Coat half of each egg to be tested with toothpaste before placing the eggs in different beverages. Does toothpaste protect eggshells from dissolving or staining?

References

https://sciencing.com/science-fair-project-tooth-decay-6085859.html
https://www.easy-science-experiments.com/rubber-egg.html

To view past “ChemShorts for Kids” activities, go to:

https://chicagoacs.org/ChemShorts

- PAUL BRANDT