Follow these instructions and find out how to make a bouncy rubber egg. This activity is a fun way to learn about the chemical reactions that occur when you put an egg in vinegar!

You will need

  • hard-boiled egg, with shell on
  • glass of vinegar.

What to do

Use a chemical reaction to dissolve the calcium carbonate that keeps the egg shell strong to make a "rubber" egg

To make your egg bounce you will need to:

  1. Put the egg into the vinegar - you should see bubbles start to form on the egg.
  2. Leave the egg undisturbed for at least a day. You should see some wonderful scum form.
  3. Take the egg out of the vinegar and rinse it with water. The shell will rub off.
  4. Give the egg a poke with your finger and squeeze it gently.

What's happening

Vinegar, or dilute acetic acid, 'eats up' the calcium carbonate in the egg shell, just leaving the inner membrane, or skin, of the egg behind. As the calcium carbonate is responsible for making the shell hard, the vinegar soaked egg feels soft and rubbery.

When calcium carbonate (the egg shell) and acetic acid (the vinegar) combine, a chemical reaction takes place and carbon dioxide gas is released. That's why you see the bubbles.

The chemical reaction keeps happening for about a day until all of the calcium carbonate in the egg is used up. Calcium carbonate is in eggshells, seashells, limestone, and many other materials.

Let's have a closer look at the chemical reaction. Calcium carbonate's formula is CaCO3 and acetic acid is CH3COOH.

So the reaction is: CaCO3 + 2CH3COOH -> Ca(CH3COO)2 + H2O + CO2.

The calcium ions (Ca2+) float free in the solution. Ions are atoms or molecules that have an electric charge due to the loss or gain of electrons.


Limestone is a sedimentary rock that is largely made of calcium carbonate. It is ordinarily white, but may be coloured by impurities; iron oxide making it brown, yellow, or red and carbon making it blue, black, or grey. The texture varies from coarse to fine.

Most limestones are formed over thousands of years from the skeletons of marine invertebrates. Among the important varieties of limestone are marl, chalk, oolite, travertine, dolomite, and marble.

Acid rain causes reactions like the ones in this activity. One kind of acid rain can come from air pollution caused by burning fuels that have sulfur atoms, which when burnt produce sulfur dioxide gas.

When the sulfur dioxide mixes in with rain, it turns to weak sulfuric acid. When the acid rain hits the limestone it slowly makes it fall apart, like the egg shell did. People use limestone in buildings and statues.

This is why over time, buildings and statues are being damaged by acid rain.

If you collect small rock samples and drop them in vinegar, you may see bubbles appear, like they did on the egg. The presence of bubbles indicates that calcium carbonate may be present in the sample.

Calcium carbonate reacts with acids to produce carbon dioxide gas, which we observe as bubbles. This is called the 'acid test'. The 'acid test' is one of many tests that geologists use to determine the identity of a rock sample.

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