Ask the students to speculate about what this might mean. The next day, pour out the liquid from each jar into separate bowls. Allow the water in the bowls to evaporate. Compare the amount of solid material remaining in the two bowls. The bowl that contained vinegar will have a larger amount of solid material.
Rainwater is often acid and can erode limestone easily.
Acid groundwater dissolves limestone underground, forming caves and sinkholes. Study or visit any caves or sinkholes in your area. Examine other types of rock to see if they react to vinegar in the same way as carbonate rocks. Place some small, freshly broken pieces of rock or brick in a large plastic jar. Softer rocks such as sandstone, shale, or limestone work best.