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Daisies in STEM - Crime Scene

Today was a beautiful day. The weather was perfect. My daughter and I were looking forward to having lunch in our backyard. We set the table outside with peanut butter sandwiches and juice and went inside to wash our hands. Alas! We returned outside to find that someone had drunk our juice and eaten from our sandwiches! Who did it? It's up to the Daisies to find out.

Crime scene activities are super fun, but they need to be adapted for each grade level. We started by defining 3 basic terms in forensic science: crime scene, evidence, and suspects.

Our crime scene, marked with a caution tape, included the table and the green rug.

The evidence included fingerprints (on the cups), teeth marks (on the peanut butter sandwiches), and a mysterious white powder.

We also identified 4 suspects: Susie Lue, Baby Mia, John Doe, and Chef Fusilli.

We will use the clues from the crime scene to identify the culprit and solve the crime. The first evidence we investigated were the fingerprints on the cups. Fingerprints are unique for each person, even identical twins do not have the same fingerprints. Fingerprint's shape can generally be described as a loop, a whorl, an arch and a tented loop.

To learn about fingerprints, each girl created her own fingerprint profile. To avoid using ink (because ink is very messy) we created a dark graphite patch by scribbling a pencil on a small paper card. The girls rubbed their finger on the graphite patch, and used tape to "lift" the fingerprint from the finger. The fingerprints were placed on a paper and examined with a magnifying glass. After the girls practiced identifying fingerprints it was time to address the evidence from the crime scene. Each girl received a cup, which was a replica of the cups from the crime scene (I touched each cup with an oily hand). The girls carefully dusted the cups with coco powder to reveal and identify the fingerprints on the cups.

The girls identified 2 types of fingerprints on the cups, a whorl and a loop. Two suspects had fingerprints that matched the evidence: John Doe and Chef Fusilli. Not all the girls were able to get clear fingerprints on the cup, which was a good reason to examine the second evidence: teeth marks on the sandwiches. Just like fingerprints, dental prints are unique for each person. Dental prints can be examined by folding a Styrofoam plate in half and biting it. This is really fun for kindergartners since at this age most kids are loosing their baby teeth and growing permanent teeth. It is easy to see where a tooth is missing on the Styrofoam plate, in addition, the permanent teeth leave sharper bite marks compared to baby teeth.

After examining the girls teeth marks, we returned to the crime scene and carefully examined the teeth marks on the sandwiches. We compared the teeth marks with the suspects' teeth, and concluded that Susie Lue and Baby Mia are probably not the culprits.

The final evidence was a mysterious white powder. We needed more information to identify the powder, so we looked for additional clues by reviewing the suspects background information. We found that Susie Lue loves eating cookies and her clothes are often covered with powdered sugar; Baby Mia may have baby powder on her clothes; John Doe is working on his science project and is using baking soda for his volcano; and Chef Fusilli likes to bake snickerdoodles with lots of cream-of-tartar. Therefore, the mysterious powder at the crime scene could potentially be powdered sugar, baby powder, baking soda, or cream-of-tartar. The mysterious powder can be identified by analyzing the chemistry properties of the powder against the known powders associated with the suspects.

The girls tested 4 chemical properties of the powders: smell, water solubility, reaction with acid, and acidity (pH) and marked the results on a results matrix.

For the smell test, we assessed the powder's smell with the wafting technique, which is used to safely smell chemicals in a laboratory. In this technique the smell is brought to the nose by waving a hand above the powder in the direction of the nose. It is unsafe to smell chemicals directly. The girls marked if the powder had a smell (baby powder) or not.

The water solubility test was done by mixing the powder with water. The girls marked if the powder dissolved completely (powder sugar), dissolved a little (baking soda, cream of tartar, and mystery powder), or did not dissolve (baby powder).

For the acid test, the powders were mixed into vinegar. The girls marked if the mixture bubbled (baking soda) or not.

Finally we tested the acidity (pH) of each powder using a home-made pH indicator - cabbage juice. The girls marked if the mixture turned pink (cream of tartar and mystery powder), stayed purple (powdered sugar and baby powder), or turned blue (baking soda). More information about the cabbage juice can be found in our Daisies in STEM - Magic Potion activity.

Once the results matrix was completed, we compared the chemical properties of the mystery powder to the chemical properties of the 4 known powders. The mystery powder was cream of tartar!

We returned to our suspects and identified the culprit. All the evidence lead to...Chef Fusilli!

The Daisies solved the mystery!

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