Chemical Reactions: Was the blood at the scene the "real McCoy"?

The lab activity is designed to provide students with a certain amount of information (some consistent variables) for them to start working. Throughout the following days, students will have the opportunity to engage in higher-level thinking skills, written and oral expression, as well as listening to and cooperating with partners, and small and large groups.

Key Concepts:
Students will make inferences regarding information given and gleaned from the crime scene.
Students will be able to distinguish between inference and evidence by participating in the Mystery Festival.

Students will write reasons of support for their conclusions showing understanding of evidence vs. inference in their notebooks.

Vocabulary: variable, inference, evidence, control (as in science experiment), chemical change

Context in Use:
Grades 4-8 would be appropriate
Class Size: 20-30 students per session
A lab or room that can be locked when not in use would be ideal, but otherwise a regular classroom roped off by police tape will work.
Time for "mystery powders" and other crime scene labs: approximately 45-60 minutes (instructions given the day before) AND paraprofessional and/or parent volunteer help is strongly recommended.
Prerequisite knowledge: a working understanding of controls and variables in experiments, practice with recording data

Students are still in the groups they were put into at the start of the unit. By now, the students should have a decent rapport and skill level to delegate duties. The day prior to this activity, I would explain where each "lab" would be set up in the room. The students would follow the directions on a card at each station and record their data and additional findings in their lab reports. At the mystery powders lab, the students would look at 5 identical clear glasses filled with the same amount but different white substances in each glass. (To save on waste, have small spoons and paint trays for the students to spoon one mystery powder per paint spot and label to avoid confusion.) Remind students that the iodine used in this lab will stain and that they must be careful with it. It is also important to remind the students to take the time to wait, observe and THEN record their findings.

FOR ONE WHOLE CLASS:Label the five cups: "Blood" powder, Kendra's shoe (a suspect), Vera's shoe (another suspect), corn starch and baking soda.

Put about 1" of cornstarch in each of the cups except the one marked "baking soda".
Fill one to four small dripper bottles with iodine.

FOR EACH OF THE EIGHT GROUPS: Put one small spoonful (I use ice cream sampler spoons.) of "blood powder" in to the first compartment.

Add 2 drops of iodine and observe the color. Write your observations on your data sheet.

Do the same with the other powders, one at a time.

Circle all those that turned the same color. (Hypothesis: What does this mean?) Write on the data sheet what powder you think they are. Rinse out your reaction tray with water and a sponge. Leave it CLEAN for the next group.

The students would then rotate to a new "lab".

If you invest the time and energy in this incredibly rewarding experience, try to save the background of the crime scene from one year to the next. It takes a lot of teacher prep to complete the entire "mystery festival", but it is worth every minute. (I've had students want to extend the class period or groan with the bell rings signaling the end of the day.)

I've mentioned the use of additional hands on the lab day (one of the labs involves burning threads of yarn found at the crime scene).

After peer review, I still like the lesson I have used. However, I might try to extend the "powders" lab by providing students will all sorts of white substances (sugar, salt, powdered sugar, flour, baking soda, baking powder, cornstarch)as well as liquids (water, vinegar, etc.)that cause reactions and see if the students can create their own experiment knowing only that white powder was found at the scene of the crime and that they may find incriminating evidence in their findings.

Prior to collecting student lab results, I would like the students to journal reflections of what happened that day and any other issues they have thought about since witnessing the crime scene. I would have them answers such questions as "What have I learned?" "What do I know to be true?" "How do I know this?"

At the start of the next class period, I would have the students share some of their reflections and have students compare the content of these reflections. What are the similarities? What are the differences? With the notebooks in hand, I should have more participation from the students that tend to let others speak for them. They would have had time to think and respond accordingly.

Grade 5
Strand: 1. Nature of Science and Engineering Sub-Strand: The Practice of Science
Standard: Students will participate in a controlled scientific investigation.
Benchmark 2: Students will identify and collect relevant information and make systematic observations from a controlled experiment.