The egg in vinegar experiment is a fun way of learning about egg structure, chemical reactions, osmosis, and the scientific method. It’s a safe and non-toxic project, so it’s perfect for young investigators. Other names for the egg in vinegar experiment are the naked egg, rubber egg, or bouncy egg. The “naked” part is easy to understand, because you’re removing the shell from the egg using chemistry. The “rubber” or “bouncy” description implies the egg bounces rather than breaks. Does it work? You be the judge!
The Chemistry of the Egg in Vinegar Experiment
Vinegar contains acetic acid (CH3COOH), which is a weak acid. Egg shells are calcium carbonate (CaCO3). Acetic acid reacts with calcium carbonate, making calcium acetate and carbon dioxide. Here is the balanced chemical equation for the reaction:
2 CH3COOH(aq) + CaCO3(s) → Ca(C2H3O2)2(aq) + H2O(l) + CO2(g)
The calcium acetate dissolves in water, while the carbon dioxide is a gas and forms bubbles. So, the egg shell dissolves and bubbles away, leaving a naked egg.
What You Do
All you need for this project is an egg, vinegar, and a cup:
- Cup large enough for the egg
- Food coloring (optional)
Use either a raw egg or hard-boiled egg. The advantage of using a raw egg is that you can see into the inside of the egg when you are done. The advantage of using a hard-boiled egg is that it bounces after pickling in the vinegar. The raw egg bounces a bit too, but if you use too much force it breaks open and makes a mess.
- Place the egg in a cup.
- Pour vinegar over the egg until it is just covered. It’s okay if the egg floats a bit. If you like, add a few drops of food coloring. After about 15 minutes, observe the bubbles forming around the egg. The bubbles are carbon dioxide gas. They form from the chemical reaction between the acetic acid in the vinegar and the calcium carbonate of the egg shell. You may also feel that the cup is slightly warm. The reaction is exothermic, meaning it gives off heat. The bubbles and temperature change are two signs of a chemical change.
- Wait a day. Also note that the liquid becomes cloudy or scummy. This is the dissolving egg shell.
- If you remove the egg after 1 day, use a spoon. Otherwise, a raw egg easily ruptures. At this point, if you remove the egg, you can easily rinse away any remaining shell. But, you get better results if you pour off the liquid and add fresh vinegar. This is especially true if you want a rubber egg or bouncy egg. Wait another day or two, giving the vinegar time to get all the way into the egg.
- Remove the egg and rinse it off using water.
Learn the scientific reason why bad eggs float in water, while good eggs sink.
Science Experiments to Try
Now that you have a rubber egg, what do you do with it?
- Examine the internal structure of the egg. This only works if you started with a raw egg and not a hard-boiled one. Identify the egg membrane, yolk, egg white (albumin), and chalaza.
- Compare the egg without its shell to a normal egg. Notice that the egg soaked in vinegar is slightly larger than the egg with its shell. Why is this? The reason is because water entered the rubber egg via osmosis. The concentration of salts, proteins, and other molecules inside the egg is greater than the concentration in the cup. The egg membrane is semipermeable. It allows the movement of water, but not larger molecules. So, the egg swells with water to try to dilute the inside of the egg so it has the same concentration and outside of the egg.
Experiment: Predict what happens if you soak the rubber egg in corn syrup, salt water, or sugar water. Compare the size of this egg with a normal egg and a rubber egg. Corn syrup, salt water, or sugar water shrink the egg because the liquid is more concentrated the interior of the egg. Here, water leaves the egg via osmosis.
- Try bouncing the egg. In addition to dissolving the egg shell, vinegar also pickles the egg. It changes the conformation of protein molecules in the egg white. Because vinegar has a low pH, it also helps preserve the egg.
Experiment: Compare how well a rubber egg bounces depending on whether you started with a raw egg or hard-boiled egg.
Can You Eat the Egg?
Eating an egg after soaking it in vinegar is not a great plan. First, it won’t taste great. Second, it could make you sick. If you must eat your experiment, soak a hard-boiled egg in vinegar in the refrigerator for a few days.
Does the Egg in Vinegar Smell Like Rotten Eggs?
Mostly, the egg comes out of this project smelling like vinegar. Vinegar pickles the egg, which preserves it. But, once you remove the egg from vinegar it starts decomposing. After enough time, if you break the egg, it will stink. The odor comes from hydrogen sulfide gas, which is a product of the decomposition reactions in the egg.
Of course, if you start the project with a rotten egg, all bets are off. Rupturing the membrane releases any trapped gases. Bounce these egg with care!