Short answer: the shell dissolves and you get a squishy, bouncy egg — if you’re patient
Put a raw chicken egg in vinegar and within a day the chalky shell starts fizzing away. After about 24–48 hours the hard shell is gone, leaving the thin membrane that holds the egg together. Keep it in vinegar a bit longer and water moves through that membrane, the egg swells, and it becomes surprisingly rubbery and even a little bouncy.
Why this happens (the chemistry, simply)
This is one of those kitchen experiments that’s predictably delightful. Eggshells are mostly calcium carbonate — basically biological chalk. Vinegar contains acetic acid. When acid meets calcium carbonate a chemical reaction happens and carbon dioxide is released as bubbles.
The reaction, in one neat line
CaCO3 + 2 CH3COOH → Ca(CH3COO)2 + CO2 + H2O
So the solid shell (CaCO3) turns into a dissolved calcium acetate, you see fizzing CO2 bubbles, and what’s left is the egg’s inner membrane.
What you’ll see, hour by hour (rough timeline)
Small changes are visible quickly and the dramatic ones happen over days. Times below assume room temperature and ordinary 5% white vinegar.
First 0–30 minutes
- Fizzy action where the shell touches the vinegar. Little CO2 bubbles cling to the surface like tiny pearls.
- If you tilt the jar you’ll see bubbles stream up — that’s your chemical reaction in motion.
6–24 hours
- The fizzing slows as the outer shell dissolves; you might see thin patches where the shell is thinner.
- If you gently touch the egg (with a spoon) you’ll feel grit from loose shell fragments.
24–48 hours
- Most of the hard shell is gone. The egg looks odd: slightly translucent, with a pale membrane visible beneath.
- It’s fragile but intact — handle carefully.
48–72+ hours
- The egg will often swell noticeably. Vinegar (mostly water) moves through the semi-permeable membrane into the egg by osmosis, making the yolk and white expand.
- Put it on a soft surface and drop from a short height and — sometimes — it bounces. It’s not a rubber ball, but it has surprising spring.
Why does the egg swell and feel rubbery?
Two things happen after the shell is gone. First, the membrane is semi-permeable: water molecules can pass through, but large proteins and salts inside the egg mostly can’t. Because the inside of the egg has dissolved proteins and salts, water moves in to balance concentrations — that’s osmosis, and it makes the egg grow.
Second, the membrane’s structure of fibrous proteins gives it elasticity. When it’s full of water it feels soft and rubbery rather than brittle.
How to do the experiment (materials and steps)
Materials
- One raw egg (room temperature is easiest)
- Clear container or jar (so you can watch)
- White vinegar (5% acetic acid) — enough to cover the egg
- Optional: food coloring, measuring cup, timer, spoon
Steps
- Place the egg in the jar gently and pour vinegar over it until it’s fully submerged.
- Watch for fizzing. Leave the jar undisturbed on a counter or windowsill.
- Check after 24 hours. If you want the shell gone, carefully pour off the vinegar and rinse the egg under water, using a spoon to rub off any remaining shell bits.
- To keep it for a bounce test, put it back into fresh vinegar for another day or two. If you want the egg to swell more, leave it in the vinegar longer and the membrane will let more water in.
Variations and little experiments to try
Once you’ve got the basic “naked egg,” you can branch into a bunch of fun mini-tests.
Try different acids
- Lemon or lime juice will also dissolve shells, but they’re weaker and smell fruity.
- Cola will fizz and slowly dissolve some shell because of phosphoric acid, but it stains and is messier.
Test osmosis by changing the liquid
- Put a naked egg into plain water — it may still swell, but less quickly than in vinegar.
- Put it into a high-sugar syrup or concentrated salt solution — watch the egg shrink as water flows out of the egg to the saltier outside. It’s a neat reversible experiment.
Dye through the membrane
Add food coloring to the vinegar. The dye can pass through the membrane, tinting the white and sometimes the yolk. It’s an arts-and-science crossover.
Measure CO2
Hold a balloon over the jar mouth when you first put the egg in vinegar (only for a tightly sealed small-mouth jar) and you’ll capture some CO2 as bubbles inflate the balloon. Tiny demonstration of gas release.
Safety and practical notes
Don’t eat the egg after this experiment. The chemistry and soaking mean it’s not food-safe. Dispose of the vinegar and egg in household waste (double-bag if it’s been sitting a long time; it can smell a bit). Rinse the jar and clean surfaces.
Vinegar is mildly acidic — it will irritate skin if you’re handling lots of it, so don’t soak your hands in it. Kids should do this with supervision. Use gloves or wash hands after handling the egg.
Common questions
Will the egg always bounce?
Not necessarily. A well-soaked egg that has swollen and the membrane is intact will bounce a little from a low height, but it’s fragile and can burst if dropped hard. The bounce comes from elasticity plus internal pressure from added water.
How long until it’s completely shell-free?
Most shells dissolve within 24–48 hours. Very gently rubbing the surface can remove stubborn bits. If you want to avoid handling a fragile egg, refresh the vinegar and wait another day.
Why does it smell sometimes?
If the egg is left too long without fresh vinegar or is punctured, hydrogen sulfide (the rotten-egg smell) and other breakdown products of protein can develop. That’s a sign to throw it out.
Why this is a lovely little science trick
It’s simple, visual, and hits chemistry, biology, and physics in one experiment: you see a chemical reaction (shell dissolving), biological structure (membrane function), and physical behavior (osmosis and elasticity). It’s tactile, a little gross in the best possible way, and reliably surprising.
If you usually think of eggs as breakfast staples, this flips that idea: suddenly an egg becomes a clear, squishy object that reveals how living structures control movement of water and gases. That’s the kind of small pivot in thinking that sticks with you.
Curious follow-ups
- Try weighing the egg before and after to quantify water gain or loss.
- Compare eggs from different species or store-bought vs home-laid — shells vary in thickness and composition.
- Microscope lovers: look at shell fragments and the membrane under magnification. The porous architecture is gorgeous and weirdly architectural.
Final thought
This experiment is like a mini science festival in a jar. It’s quick to set up, needs only grocery-store supplies, and gives you a chain of observations to follow. Plus, you can say you made an egg bouncy — which never fails to delight.