What it shows
An eggshell is calcium carbonate, which reacts with the acid in vinegar and fizzes away as carbon dioxide, leaving the egg held only by its soft membrane. The rubbery egg also swells, showing that water passes into it through the membrane.
The science
Eggshell is mostly calcium carbonate, the same substance as chalk and marble. Acetic acid in vinegar reacts with it to give calcium acetate, which dissolves, plus water and carbon dioxide gas, seen as bubbles on the shell. After two days the shell is gone and the egg is held by a thin membrane. The membrane lets water in but keeps the large proteins inside, so water moves in from the vinegar, which is mostly water, and the egg swells.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- One raw egg
- A glass jar with a lid
- Enough vinegar to cover the egg, about 1 cup
- A spoon
- A ruler and a kitchen balance, optional
- Golden syrup or strong sugar solution for the extension
Safety
For this project: The egg is raw, so wash hands after touching it and keep it off food surfaces. Bounce the finished egg only from a few centimetres over a tray; it bursts if dropped from higher.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Measure the egg around its middle with a string and ruler, and weigh it if you can.
Put the egg gently in the jar and pour vinegar until it is covered.
Watch for small bubbles covering the shell within a few minutes; these are carbon dioxide.
Cover loosely and leave for a day; then pour out the old vinegar and add fresh vinegar.
After two to three days lift the egg out with the spoon and rinse it gently under a tap.
Rub off any remaining white film with your thumb to reveal the translucent, rubbery egg.
Measure and weigh it again, and compare with the first numbers.
Hold it up to a torch to see the yolk shadow, then bounce it gently from 3 cm onto a tray.
What you should see
The shell disappears completely, the egg is larger and heavier than before and looks translucent, and it bounces a little from a low height before bursting.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is the eggshell made of?
Calcium carbonate, like chalk.
2What were the bubbles on the shell?
Carbon dioxide gas made when the acid reacted with the shell.
3Why did the egg grow bigger?
Water from the vinegar passed into the egg through the membrane.
4What happens to teeth that sit in acidic drinks?
Acid attacks the hard minerals in enamel in the same way, so teeth are damaged.
Take it further
Put the naked egg in strong sugar syrup for a day and watch it shrink as water moves out again.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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