STEM Explorer Day 2: Mock CSI Crime

Welcome to Day 2 where your STEM Explorer solved a CSI Mock Crime using Forensic Science.

Today we were detectives and used paper chromatography to figure out which of five different black pens was used to write the letter left at the crime scene. Paper chromatography is a separation technique in which dots of pigment, in our case ink, are placed on special filter paper and the paper is then dipped into a solvent. We used 70% rubbing alcohol as the solvent, and as the alcohol traveled up the paper, it dissolved the dots of ink and carried them along with it. Since black ink is actually a mixture of several different colors, or pigments, the colors get spread out on the paper because they have different affinities to the paper. At the end of the experiment, we took the papers out of the alcohol and these were our chromatographs.
We then were able to compare our chromatographs to the “unknown” chromatograph to figure out which pen was used to write the letter.

Blood Composition and Compatibility

Are you my Type?

Even though blood has been studied for thousands of years, the discovery of different blood types was not made until 1901 when Dr. Karl Landsteiner identified the ABO blood groups. Landsteiner was awarded a Nobel Prize for discovering that each blood type is based on two different antigens, A and B, which are molecules located on the surface of red blood cells.

In today’s lesson, explorers learned all about blood, had an opportunity to view blood cells under the microscope, and participated in a hands-on laboratory activity investigating blood typing. Explorers used simulated blood to determine each of the suspects blood type.  Ask your explorer how they determined the blood type of each suspect!

For an Extension, try this virtual game:

Hair Identification

Today in class, Explorers acted as forensic scientists by identifying hair samples! First, we discussed who actually has hair (only mammals) and some functions of hair on animal bodies (e.g., for UV protection, for camouflage, for sensory tools like whiskers).

Then Explorers examined cards with microscope images of unknown hair samples and compared them with a master key of hair medullas in order to determine the species of each hair sample. Once they were hair experts – and could tell a dog hair from a rabbit hair – explorers determined what type of hair was left at the crime scene.

Exploring Fingerprints

No two fingerprints are exactly alike. But why are they different and how do forensic scientists use them to solve crimes? In this lesson, we took a close look at the unique features of fingerprints. Explorers learned that fingerprints come in 3 basic varieties: arch, loop, and whorl. The majority of people have loops, while only 4% of the population has arches. Fingerprinting has been used to catch criminals for over 100 years. Plastic, patent, and latent prints are three types of fingerprint evidence that can be found at a crime scene. Explorers even had a chance to try their skill at taking their own fingerprints and learned how to dust and lift prints. Perhaps a career in forensics is in your explorer’s future?

Chemical Identification—Identifying the Unknown

Today, we examined six white powdery substances and performed experiments to help us identify what each one could be. The six substances were all very common household items- baking soda, cornstarch, sugar, salt, chalk, and borax. We examined which of these substances were soluble in water and in alcohol, which ones reacted with vinegar and which ones turned a color in the presence of iodine. We found that each white powder has its own set of characteristic physical properties and chemical interactions with our test solutions. For example, baking soda reacted vigorously with vinegar (ever tried a homemade volcano? It’s usually baking soda and vinegar that create the bubbling “eruption”), while cornstarch turned a cool blue color when we added iodine to it. We learned that “you can’t judge a book by it’s cover” any more than you can judge what a white powder is by just looking at it. In both cases, experimentation or further analysis is needed to find the true identity of an unknown!



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Our Young Pre classroom is for ages. This age group is working