One of our big labs of the year is the Mystery Powder Lab. I have 6 unknown white powders that the students have to identify by performing a series of chemical tests and observing physical properties. Once they have all their data collected, they use a flow chart to figure out the identity of each powder.
On a plastic tray, I set up the following equipment: one flask of vinegar, one flask of iodine, one flask of cabbage juice, 3 pipettes, cup of clean toothpicks, cup for used toothpicks, microwell plates, 6 numbered plastic knives, and a test tube clamp. I stress the importance of avoiding contamination and proper lab procedures. When the bags are not in use, they should be closed and put back, never put anything back into the bags once its been used or touched any surfaces (besides the knives), to only use knife # 5 for powder #5, not to let the pipettes touch the powders they are testing, if anything spills or breaks to let me know, etc. The plastic trays help keep everything contained, the powders do get messy and some stuff will spill or overflow. Very easy to clean up between classes when it’s all on the trays.
On the side of the classroom, I have the 6 mystery powders in small zip-top bags, 4 of each one. The powders are: baking soda, baking powder, flour, corn starch, sugar, and baby powder (no cornstarch kind). I have pre-cut aluminum foil squares for the heat test next to the bags, the students take one when they are ready to use it. Under the hood, I have candles set up for the heat test.
Students can test the powders in any order, as long as their data is written next to the corresponding number on their data chart. The tests that they perform are: Cabbage Juice to practice pH, vinegar to test for fizzing, and iodine to test for the presence of starch, and the heat test to test for sugar. For the heat test, you want a caramel color and bubbling for a positive test, all the other powders either scorch or don’t do much.
The students perform this lab in groups of 3-4 and it takes about 1 1/2 class periods to complete. Once they have collected all their data and made their observations, I give them the flowchart to identify the powders. As a group they evaluate their data and write down what they think each bag contains. We go over the answers the next class period, or if everyone is done before the end of class, we go over the answers then. Kids really enjoy this lab and work well as a group. They take turns doing the different tests and discuss what is happening during the lab.
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