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Make a cave

You will need:

  • A chalk block, the bigger the better
  • Vinegar or a weak acid


1. Carve out a small hole inside the chalk block. You can just crush up the chalk to speed the reaction

2. Fill the hole with vinegar and allow the vinegar to react with chalk (you should see small bubbles)

3. Pour out the liquid once you see no more bubbles (this may take some time).

4. Add some fresh acid to the hole and allow the liquid to react again with the chalk. Repeat & repeat.

5. Is the hole starting to get bigger? Why? Where does the chalk go in the reaction? Check below...
Be Amazing Book Front Cover; Ben Newsome, teacher & founder of Fizzics Education. Be Amazing -how to teach science the way primary kids love
Be Amazing!
How to teach science, the way primary kids love

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Why Does This Happen?

Chalk is made up of a type of limestone, a compound made of Calcium and Oxygen. Chalk is formed by the shells of microscopic marine organisms, often containing fossils from ancient seabeds. Vinegar reacted with the chalk to produce Carbon Dioxide gas, water and an aqueous compound.

2CH3CO2H(aq) + CaCO3(s) > 2Ca(CH3CO2)2(aq) + CO2(g) + H2O(l)

Limestone caves are formed when the limestone itself is dissolved by weak acids present in groundwater. This process occurs over many years and can eventually lead to forming massive formations as seen in the Jenolan caves.

A similar process occurs when acid rain touches marble statues... a major issue in historic areas.
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