The eggshell is made of calcium carbonate (a base), and the vinegar is made of acetic acid (an acid). Acids and bases are the opposite of each other and usually react when added together.

Calcium carbonate – the main component of mussel shells, pearls, and the shells of many other marine organisms – is highly reactive with acid, so the shells should have dissolved completely.

Scientists have discovered a spongy form of calcium carbonate (CaCO3), a material found in limestone, chalk, marble, and the shells of mussels and other shellfish. While most forms of calcium ...

Vinegar is a solution of acetic acid in water, usually at about 5 percent, with a pH of 2.4. Lemon juice contains ascorbic acid and citric acid, with a pH of about 2.3.