You will need:
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...