An estimated 3% of vinegar is composed of acetic (ethanoic) acid. Meanwhile, an eggshell is mostly composed of calcium carbonate. When acetic acid and calcium carbonate are combined, they form calcium acetate, water and carbon dioxide. This combination physically and chemically changes a non–water-soluble chemical like calcium carbonate into a water-soluble compound (calcium acetate and carbon dioxide gas).
The reaction created by acetic acid and calcium carbonate can be written as the equation CaCO3+ 2H+ -> Ca+2 + H2O + CO2.
CaCO3 is calcium carbonate, and H2 is hydrogen iodide. Ca+2 is calcium cation. H2O is water. CO2 is carbon dioxide.
This osmosis experiment is a common scientific lesson in many junior high and high school classes and is a simple way to teach students chemical reactions.