What it shows
An eggshell is made of calcium carbonate like tooth enamel is mostly calcium minerals. Soaking shells in different drinks shows which ones stain and which ones soften the shell, a model for why teeth need care.
The science
Calcium carbonate reacts with acids and slowly dissolves, releasing carbon dioxide bubbles. Colours in tea and cola attach to the rough surface and stain it. Enamel is harder than eggshell, but acids and sugary drinks still wear it over a long time, which is why rinsing the mouth and brushing matter.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Five pieces of clean white eggshell, same size
- Five clear glasses or jars
- Water, cola, tea, lemon juice (diluted) and milk
- Labels and a marker
- A camera or phone
- A fork to lift pieces out
- A ruler to compare shell hardness gently
Safety
For this project: Do not drink any test liquids afterwards. Wash hands after handling eggshell, which can carry germs. An adult should boil the shells first. This is a model; it does not replace a dentist’s advice.
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.
Boil the eggshell pieces for five minutes with an adult, cool them and dry them.
Label the five glasses with the drink names and pour 100 ml of each drink in.
Take a photo of each shell piece beside a white card for the starting colour.
Place one shell piece in each glass so that it is covered.
Photograph the glasses after 1 hour, 1 day and 3 days.
Lift each shell out with a fork, rinse it with water and look for stains or bubbles.
Press a shell gently with a fingernail to compare how soft each has become.
Rank the drinks for staining and for softening in a table.
What you should see
The shell in water is unchanged, while those in tea and cola show stains and those in acid drinks look duller or softer. Milk shows little change.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why use eggshell?
It is calcium-rich like enamel and easy to see.
2What causes the bubbles?
Acid reacting with calcium carbonate to release carbon dioxide.
3What is the control?
The shell in plain water.
4How does this relate to teeth?
It suggests that acidic and sugary drinks, if frequent, can harm teeth.
Take it further
Test how brushing the stained shell with toothpaste changes its look.
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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