Looking for something fun, engaging and educational to do with your kids this summer? Here's the recipe and instructions for the Sidewalk Chalk science experiment that our Tuesday morning guests referred to. Have fun!
Making Sidewalk Chalk
Required Supplies:
Water
Plaster of Paris
Poster Paint (various colors)
Mixing Container (small paper cups, bathroom dispenser size)
Stirring Utensil (e.g., popsicle sticks)
Mold (e.g., paper coin wrappers – preformed)
Old newspapers of paper towels
Recipe:
Approximately 1 part water (e.g., 1/8 cup)
2 parts Plaster of Paris (e.g., ¼ cup)
Poster paint to provide color
Procedure:
- In the mixing container put the Plaster of Paris. Stir in enough water with the Plaster of Paris that the mixture has the consistency of ketchup (you’ll need to be able to pour it, but you don’t want it to be too runny).
- Add enough poster paint to make the mixture the desired color.
- Position the mold. If you are going to use coin wrappers, stand the coin wrapper on one end on the newspaper or paper towel.
- Pour the mixture into the mold and leave it along until it hardens. If you use a coin wrapper, once the mixture has dried, you can just peel the wrapper away from the chalk (the wrapper will peel away easier if the chalk still has a little moisture in it).
- Depending on how much water is in your mixture, the paper should be removed after 1-1.5 hours. Also, the chalk will need to dry out for about 1 day before using it so that it doesn’t crumble.
NOTE: do not put Plaster of Paris in the sink. It clogs pipes. Throw used materials in the trash.
Science aspects:
Evaporation – As the water evaporates from the Plaster of Paris, what was once a powder and a liquid is now a solid. Sometimes during the evaporation process, you can detect heat also.
Filter – If you used a pain coin wrapper and placed it on a newspaper or paper towel, you will see that the water absorbed by the newspaper or paper towel is clear, not the color of the chalk. The Plaster of Paris must act as a filter… the water molecules are small enough to filter through the mixture, but the molecules containing the color are not.
Instructions for removing chalk from wrapper:
Allow chalk to harden. After 1-1.5 hr. peel away the wrapper from the chalk (The wrapper will peel away easier if the chalk is still a little moist). Allow chalk to dry out for one day before use.
