Answer: The acetic acid in vinegar makes the calcium water-soluble.
This mild acid attacks the calcium phosphate, freeing the calcium molecule to be dissolved in the residual water. The formula for this reaction is
CaCO3 + CH3COOH –> Ca + H2O + CO2.
Earth science classes demonstrate vinegar’s effect on calcium with two popular experiments. One is the Flexible Chicken Bone, in which chicken bones are soaked in vinegar for several days or even weeks, turning them soft and flexible. This happens because all the calcium has been removed from the bones, leaving only the soft collagen and elastin parts, which bend easily.
The second experiment is called The Transparent Egg, in which a raw egg is soaked in vinegar for a few days, which removes the calcium coating from the shell, leaving the protective, transparent membrane. The Transparent Egg is used for further experiments demonstrating osmosis and diffusion.
Pliny the Elder told a tale regarding a bet Egyptian Queen Cleopatra had made with Roman Emperor Marc Antony. She claimed she could throw a more expensive banquet than he could. Antony accepted, naturally, because Roman parties, and his parties in particular, were world-famous. When Antony arrived for the feast, he felt sure of his impending victory. Cleopatra’s table was set with only a goblet filled with wine vinegar. However, she removed a pearl from her very earring, which was worth 15 kingdoms. She dropped it into the goblet. After it dissolved, she drank it. Antony conceded his defeat.
“Science of Eggs: Making Naked Eggs Activity.” Exploratorium: the museum of science, art and human perception. N.p., n.d. Web. 9 Aug. 2010. http://www.exploratorium.edu/cooking/eggs/activity-naked.html.
“Chemical Reactions.” NEWTON. N.p., n.d. Web. 9 Aug. 2010. http://www.newton.dep.anl.gov/askasci/chem99/chem99442.htm.
“How Cleopatra Won Her Bet : Discovery News.” Discovery News: Earth, Space, Tech, Animals, Dinosaurs, History . N.p., n.d. Web. 9 Aug. 2010. http://news.discovery.com/history/cleopatra-pearl-cocktail.html.