Don’t be Deceived by Appearances

Chemical Identification—Identifying the Unknown

Students became chemistry sleuths in the science lab this week. In this lesson, we discussed how to identify a chemical without the use of complicated machines. Students learned that in addition to using their senses, they could also use chemical properties for identification. Each group of students was given six known white powders to test (baking soda, borax, chalk, sugar, salt, and cornstarch) and using the data they collected from a series of 4 tests, they were then able to use their results to identify an unknown white powder.

They performed tests of three different properties: solubility, reactivity, and decomposition with heat, in order to identify their unknown sample. They observed which samples dissolved in water and/or in rubbing alcohol, which reacted with vinegar or iodine (if a substance reacted with vinegar the students observed bubbling, and if a substance reacted with iodine, it turned purple!), and what happened when we held a sample over a flame (nothing, popping sounds, smoke, or perhaps the delicious smell of caramel!). Working collaboratively, they determined the properties of each known sample. They then used their results to determine the identity of their unknown, which turned out to be a combination of two of the white powders already tested. Students did a great job staying focused on their experiments and collecting the data they needed to identify the unknown.

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