Mystery time! Can you figure out what the four white substances are? This lesson can be used to show properties of difference substances or demonstrate differences between chemical and physical changes. Or it can just be for fun!
I introduced this investigation to students after discussing chemical and physical properties of substances. For a “warm-up” I asked the students if they would ever accidentally mistake glue for milk. “Gross!” seemed to be the normal response. However, they easily listed several reasons – color, viscosity, density – it was clear which liquid students could drink. I even showed students what happens when you mix vinegar with both. Again, they were grossed out by the curdling milk.
Powder Investigation Set Up
Before class, I prepared the lab for the students. Containers A, B, C, D were filled with a different white powder. I also included a magnifying glass, beakers of water and vinegar and an eye dropper in their lab baskets. Sheets of foil were ready for them to use as “plates” or testing stations for their powders as well. I do use iodine, because this makes a chemical reaction with one of the powders, but I don’t let any of the students handle it. and we put any iodine mixture in separate spaces.
I placed cornstarch in container A, salt in container B, baking soda in container C and sugar in container D. Feel free to use other white substances (safe ones please!), but I chose these four because I had them available in my classroom, and they are “safe” to use. Remember… middle schoolers want to eat everything. I’m not going to use things that might put them in danger! Each substance also has a unique reaction to at least one of the tests that students can choose from. Cornstarch changes the color of iodine, salt has crystal-like particles, baking soda fizzes with vinegar, and sugar tastes sweet!
Time to test!
I let students choose which tests they would like to do with the substances. This includes mixing the substances with water, vinegar, or iodine, feeling the textures of each, using the magnifying glasses to observe the particles, and of course, the taste test (but I make them wait to do this last so it is not a giveaway!)
It is important to emphasize where students may see chemical changes happening. I ask the students these questions:
Are there bubbles?
Was there a color change?
Did something new form?
Can you get the substances back?
While testing, students fill out a chart like this: MysteryPowders. A “P” is placed in the blank if a physical change occurs and a “C” for any chemical changes.
At the end of the time, I do tell the students what each of the substances were and they are excited whenever they guessed correctly!
Have fun investigating!