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I'm not sure what grade level in elementary you are working with. When I teach states of matter, I like to ask can matter change its state? How do we know if it is a chemical or physical change?
I bring in sets of balloons that all look the same size. Each group gets a set of 3 and they have to decide which state it is in and as much information as they can gather about the balloons in about 3 minutes. One balloon is filled with air, one with water, and one with ice. I freeze a water filled balloon the night before and keep them in an ice chest. We discuss the properties of each state. What would have to happen in order for the solid balloon to change its state, the liquid to change its state?
Then on another day we discuss the difference between physical and chemical changes. We put 1 tbsp of vinegar in an empty water bottle. put 1 tspn of baking soda in a balloon and carefully place the mouth of the balloon over the bottle without spilling the contents. Then we make a prediction about what will happen when the two mix. Most 3rd - 5th graders know what will happen. We then count down to drop in the baking soda and record what evidence we have observed to determine which type of reaction we are seeing.
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