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Plaster of Paris
Plaster of Paris can be combined with water to form a chemical reaction. Most commonly, plaster is the compound gypsum that has been heated. See Plaster and Portland Cement for more information about Plaster of Paris and cement.
I. Making Plaster
• Place a tablespoon of Plaster of Paris in 1 tablespoon of water. This can be done in a wide mouthed paper or plastic cup. Make sure that you add the plaster on top of the water so that the water can slowly absorb the powder. After the plaster appears completely wet, mix the two materials thoroughly.• Continue to stir over several minutes and describe the reaction.• As the mixture sets and becomes hard, have students feel the sides of the cup and note any temperature change.
SAFETY NOTE: Plaster of Paris is safe, but with all chemicals and powders it is important that students not aspirate the plaster dust. Plaster of Paris is a mild base and may cause some dry skin from prolonged exposure. Students should wash their hands when the experiment is completed.
II. Making Porous Plaster of Paris
Now we know how to make Plaster of Paris and we know how to make CO2. Let's combine these two reactions.
• Mix 1/16 of a teaspoon** of baking soda and 1 tablespoon of water
• Place a tablespoon of Plaster of Paris in this mix. Make sure that you add the plaster on top of the water so that the water can slowly absorb the powder. After the plaster appears completely wet, mix the two materials thoroughly,
• Add 1/16th of a teaspoon of Creme of Tartar and mix thoroughly
**In order to measure 1/16 of a teaspoon, one must estimate 1/2 of an 1/8 measure--the smallest normal size in a kitchen set of measuring spoons.
If you have a 1/4 teaspoon, it can be separated into 4 equal portions using a sharp edge making 1/16th portions.
If you have a triple beam balance, you can use grams and create a more refined way of measuring.
Describe the outcome. Noting that the plaster now contains bubbles, describe the nature of this new mixture (a combination of two different compounds). We will use this knowledge to design some experiments to test the concept of the plaster pot filter.
C02 Bubbles in the set plaster
During these processes, have students use their STEM notebooks and encourage them to:
• Record notes of demonstrations, experiments, or other input in a systematic way.
• Collect data carefully, in a manner consistent with scientific processes.
• Summarize main points or science concepts.
• Use diagrams, lists, and narrative in appropriate ways.
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