Summary

In this activity, students will determine empirical formulas for samples of trace evidence collected from various crime scene scenarios. They will use the information to link a criminal to a particular crime scene.

Grade Level

High school

NGSS Alignment

This activity will help prepare your students to meet the performance expectations in the following standards:

• Scientific and Engineering Practices:
  • Using Mathematics and Computational Thinking
  • Analyzing and Interpreting Data

Objectives

By the end of this activity, students should be able to

• Determine the empirical formula from percent composition or mass data.

Chemistry Topics

This activity supports students’ understanding of

• Percent composition
• Empirical formula

Time

Teacher Preparation: 15 minutes

Lesson: 30 minutes

Materials

• Case Description Cards
• Suspect Cards
• Calculators
• Periodic Table

Safety

• No specific safety precautions need to be observed for this activity.

Teacher Notes

• This is intended to be used an individual activity but can be differentiated to partner work.
• There are 8 “Case Description Cards” provided which each require the empirical formula to be determined. Each case is provided with percent composition data as well as with mass data. Teachers can decide to use one type of card or the other, or a combination of both.
• 8 “Suspect Cards” are provided and are used by students to match the empirical formula that they determine to the suspect of a crime.
• Students are required to show work for each case and determined whodunit on the Student Handout.
• Students should have a background on calculating empirical formula from percent composition or mass values (depending on the card type chosen by the teacher) prior to completing this activity. Students should also be familiar with differentiating between empirical and molecular formulas.
• The case cards may be solved individually. I suggest printing a set of case cards for 4 students to share in order to allow the cards to be passed efficiently.
• To differentiate, one could assign the entire set to two students to share the load. The red cards may be a little more difficult to solve, and could be assigned to advanced students.
• Teacher could print on cardstock or colored paper and laminated to ease material handling and allows for better re-use between classes.
• Teacher should print out suspect cards. These cards should be placed on a large “Suspect Board” (magnets or tape to large blackboard or whiteboard or semi-permanent poster). This allows for more interactive solving, as students become quite competitive as to who’s the best “detective”.
• Alternatively the teacher could print the suspect cards for the groups as was done for case cards. In this event, suspect cards should not be distributed until about half way into the activity, to allow for clarity of tasks (students should have most of the formulae from the cases done by then).
• Answer Key: