4-H STEM: Crime Scene Investigation

Back in December we did what I think was the funnest activity yet with our 4-H STEM group.  We did a crime scene investigation that incorporated some chemistry, some biology, some physics.

The Set-up:  A crime has been committed.  The sugar cookies for the party have been stolen.  We  will be examining the trace and physical evidence left at the scene to determine our guilty party.

Our suspects:

Beary Cedric AKA Cedric the Bear

Seen near the scene of the crime with white powder on his paws

Richard Odod the Dodo

Also seen near the scene with white powder on his hands....er wings

Oscabolla the horse

Seen leaving the scene

Also seen near the scene of the crime were Pikachu and an unknown human.

Our first activity was to identify the unknown powders that were found on Cedric and Richard's paws/wings/feet.

We tested a variety of white powders: baking soda, baking powder, corn starch, and detergent with different reactants - iodine (reacts with starch), vinegar (a weak acid that will react with bases), and cabbage juice (pH indicator) and recorded the results.

We then processed our reactants with our two unknown powders and compared the reactions to our known substances.

To make it easier, each group was provided with an ice cube tray to separate the samples.

Our results: Cedric had baking soda on his paws, while Richard had cornstarch on his wings.  So far the evidence is inconclusive.

We then dusted some plates found at the scene for fingerprints.  I set up the plates ahead of time by putting lotion on my hands and pressing my fingers against the edge of white ceramic plates.

The kids used cocoa powder and soft brushes to bring out the fingerprints.  It was very important to tap lightly with the brushes, not brush back and forth.  We then used tape to lift the fingerprints off the plates.

We then used markers (the lab sheet said to use pencil but our pencils didn't work for some reason) to make an impression of our own fingerprints and compared them.

Our last activity was using short wave UV lights to look for clues around the scene.  We discussed the various things that will show up under the lights, which include blood, saliva, sweat, scorpions, some vitamins, milk, some oils, honey, ketchup and various other organic materials.

I used yellow highlighters and wrote messages on black cardstock so they would only show up under the lights.  I placed these in semi-hidden spots around the room.

My signs:

  

Our guilty parties were: Cedric the Bear and Oscabollo the horse.

The kids had a great time with this activity and were very excited when they solved the crime.