Wondering Why?

Why Does Vinegar dissolve Egg shells?

Why Does Vinegar dissolve Egg shells?

Vinegar has a chemical substance called acetic acid (about three percent of vinegar). Egg shells are composed of calcium carbonate. When egg shell reacts with vinegar the calcium carbonate reacts with acetic acid to form carbon-di-oxide. This gas appears as small bubbles inside the vinegar.

CaCO3 + 2 H+ à Ca2+ + H2O + CO2

Here, the share of acetic acid is two protons. An acid in water provides protons in the solution. Vinegar will dissolve the egg shell but keeps the membrane intact. This means that egg shell can be removed but the egg can be kept as it is. This is due to acetic acid in the vinegar. The egg shell has calcium carbonate and the acetic acid divides the egg shell from the egg allowing the shell soluble in the vinegar. The calcium ions will move off from the egg into the vinegar and carbonate converts into carbon-di-oxide.
The acidic vinegar divides the calcium carbonate of the shell to form calcium acetate. Calcium acetate dissolves retaining the thick membrane covering the hard boiled egg. The resulting product is an egg without the shell. Calcium acetate separates in the solution as calcium ions and acetate ions. The acetate was not shown in the formula and hence the number of water molecules formed in order to balance the reaction is not known. Hence, many complexes of ions, CO2, and water are in equilibrium with the solution.
If the shell of the egg is dissolved by acetic acid in the vinegar, the cell membrane that surrounds the inner egg appears. This membrane does not react with the acetic acid and because of this layer, the yolk and the egg white will not spread out when the outer shell is removed. The cell membrane is semi-permeable which means that some water can enter the egg yolk and white and make it expanded.


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