What does the coke do to eggshell?

When an eggshell is placed in a glass of cola, bubbles of carbon dioxide gas will begin to form on the shell's surface. This happens because the phosphoric acid in the cola attacks the calcium carbonate in the shell, creating carbon dioxide gas. The gas bubbles will cause the shell to look cloudy and white, and eventually it will begin to dissolve.

The rate at which the eggshell dissolves will depend on the concentration of phosphoric acid in the cola and the amount of time the shell is in the cola. A cola with a higher concentration of phosphoric acid will dissolve the shell more quickly, and a shell that is left in the cola for a longer period of time will dissolve more completely.

The experiment demonstrates the effect that acid can have on calcium carbonate. Calcium carbonate is a compound found in many natural materials, including eggshells, limestone, and chalk. Acidic substances, such as cola, can dissolve calcium carbonate, which is why they can be used to clean surfaces made of these materials.