The ScenarioIn this challenge, groups of students need to use chemistry to identify the perpetrator behind a recent robbery in the chemistry department. The introductory slide is shown below: Learner ObjectivesI can:
Lesson StructureThe heart of this lesson is all about motivating students to work productively in a group setting. In my class of 30 students, I had students in groups of 4-5 but this could easily be modified to work with smaller groups as well. I wouldn't recommend getting larger than 5 or students will have a hard time contributing to their group. Setting the Stage - [3 min] Hand out “There’s Been a Crime!” and Clue #1 papers, one of each per group
Outline the Objective – “Who stole the equipment from the chemistry department?” - [5 min]
Clue Time - [10 min]
Pulling it Together - [25 min]
Conclusions - [10 min]
The Answer - [0-5 min] Depending on how students do with the task, you can end the period (or start the next period) by going over the solutions together as a class. If most groups get to the at least one of the solutions, it is usually best just to let the task naturally conclude with their conclusions. A teacher revealing the answer sometimes disrupts the feeling of personal discovery and solving a mystery. The CluesEach of the clues provide a piece of the puzzle but none of them provide enough information to solve the mystery on its own. Not all of the information in the clues is needed but since students are only allowed to bring back their notes, it's important to capture everything that might have value once combined with the other clues in the group. The SolutionClue 1: The flask contains two substances, liquid Potassium Carbonate (K2CO3) and an unknown solid that are the products of a chemical reaction. The note suggests that the precipitate is important, so this mystery substance is the perpetrator’s “calling card” Clue 2: The “calling card” is a compound that shares the same initials as the suspect Clue 3: The list of suspects can be narrowed down to 4. The atomic number of the elements listed on the slip of paper suggests that the ID must begin with “827” Clue 4: The only equation that does not have an error is the second one, suggesting that the perpetrator used a double replacement reaction to make the “calling card” Clue 5: The only metals higher than Calcium on the activity series are Lithium (Li), Potassium (K), and Strontium (Sr). Of these, only Potassium (K) is missing so the single replacement reaction creates Potassium Sulfide (K2S) Clue 6: The secret ingredient represented by the picture is Iron (II) Carbonate (FeCO3) All of these clues lead to the following reaction and identity of the unknown substance left by the perpetrator. The perpetrator is Franklin Edward Sparrow (aka “Iron (II) Sulfide”) How to help...Encourage groups to work persistently through the challenge and the feeling of being stuck. If it looks like a group has stopped making progress, it may be necessary to provide some hints to help them down a productive path. Try to limit the hints to 1-2 things that will help the group wherever they are at. Some possible hints to consider:
Materials Needed
FilesBelow are the files for the clues and supplementary materials. Please use and share freely for non-commercial purposes. If you have any questions or ideas, leave a comment below :)
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