Using soils from different parts of the Scout den..
Test the pH by mixing vinegar or baking soda to the soil.
Add water and see if it bubbles or not.
Plastic bottles for each person
Cut the plastic bottle in half
Place soil into the container (couple of Tbsp)
Add baking soda then water to the soil (same quantity as soil)
In another plastic container, fill it with soil and add vinegar then water (same quantity as first experiment)