Why Does an Eggshell Dissolve in Vinegar?

Vinegar will dissolve an eggshell, but leave the membrane intact, which means you can remove the eggshell but leave the egg intact, and yes I’m referring to a raw egg! The reason for this effect is due to the acetic acid in the vinegar. The egg shell is made up of calcium carbonate, the acetic acid breaks the two apart letting the shell dissolve into the vinegar. The calcium ions will float way from the egg into the vinegar while the carbonate turns into carbon dioxide, you’re looking at the carbon dioxide when you try this at home, it’s the bubbles that form on the egg.

Another acid that can be used is citric acid. This acid dissolves the shell faster, more completely, and with a weaker odor.

A real world application of this chemistry can be found when looking at limestone. Limestone is made out of a form of calcium carbonate. Rain water is acidic because of the carbon dioxide in the air — the carbon dioxide dissolves slightly in water to make carbonic acid. When it rains, the water works on the limestone like the vinegar does on the egg. The water slowly dissolves the limestone, eventually forming caves, stalagmites, and stalactities.