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KS2 Science at Home: Week 9

Key Stage 2 Experiment of the Week! – 'Naked Egg' Experiment

How does it work?  

Naked egg day7

The bubbles that form on the shell are carbon dioxide (CO2). Vinegar is an acid called acetic acid (CH3COOH), and white vinegar from the grocery store is usually about 4% acetic acid and 96% water. Eggshells are made up of calcium carbonate (CaCO3). The acetic acid in the vinegar reacts with the calcium carbonate in the eggshell to make calcium acetate plus water and carbon dioxide that you see as bubbles on the surface of the shell.
The chemical reaction looks like this . . .

2 CH3COOH + CaCO3 = Ca(CH3COO)2 + H2O + CO2
Acetic acid + Calcium carbonate = Calcium acetate + Water + Carbon dioxide

The egg looks translucent when you shine a flashlight through it because the hard outside shell is gone. The only part that remains is the thin membrane called a semipermeable membrane.

You might have noticed that the egg got a little bigger after soaking in the vinegar. Here’s what happened…Some of the water in the vinegar solution (remember that household vinegar is 96% water) travelled through the egg’s membrane in an effort to equalize the concentration of water on both sides of the membrane. This flow of water through a semipermeable membrane is called osmosis.

If you take your naked egg and place it in a glass filled with corn syrup, the egg will shrivel. Since corn syrup has a lower concentration of water than an egg does, the water in the egg moves through the membrane and into the corn syrup to equalize the water concentration levels on both sides.

Materials you need

  • Distilled white vinegar
  • Egg
  • Beaker

Instructions

1. Place the egg in a tall glass or jar and cover the egg with vinegar.

Naked egg day1

2. Look closely at the egg. There will likely be tiny bubbles forming on the shell.

3. Leave the egg in the vinegar for a full 24 hours.

4. Change the vinegar on the second day. Carefully pour the old vinegar down the drain and cover the egg with fresh vinegar. Place the glass with the vinegar and egg in a safe place for a week—that’s right, 7 days! Don’t disturb the egg but pay close attention to the bubbles forming on the surface of the shell (or what’s left of it).

5. One week later, pour off the vinegar and carefully rinse the egg with water. The egg looks translucent because the shell is gone! The only thing that remains is a delicate membrane of the egg surrounding the white and the yolk.

Questions to think about

1. Does the experiment change if the egg or organic or not?

2. Does using a more concentrated vinegar change anything?

Some research for next week:

We will answer this question with next week’s science experiment!