The Mystery of the Stolen Ice Cream Machine

Melissa Anderson

1-30-2014

TEACHER KIT

The Mystery of the Stolen Ice Cream Machine

Description: Students will engage in different tasks that develop varying chemistry skills. While trying to figure whom the real thief is, students will work with chromatography, fingerprint analysis, hydrometers, and acid-base chemistry.

Learning goals: Students will engage in reasoning and problem solving while solving this mystery. Each stage of the mystery will provide the students with a new area of chemistry to explore. The ink chromatography will enable the students to learn about polarity. The hydrometer provides a stage in which the students can learn how to measure sugar levels in a beverage. As an aside, the students will learn how much sugar they are really drinking when they imbibe Powerade or energy drinks. The fingerprint analysis encourages the students to practice close observation. The secret note provides a lesson in acid base chemistry.

Recommended grades: 3-7; ~45 minutes

Key Concepts:

Polarity: separation of charges within a molecule that form a dipole/multipole movement

Analysis, measuring, deductive reasoning

Acid-base chemistry: the exchange of protons between and acid and a base; a base is a proton acceptor with a pH over 7; an acid is a proton donator with a pH under 7.

Meniscus: the curve formed at the top of a surface as a result of surface tension; it can be concave or convex

Materials needed: black permanent marker, black whiteboard marker, black Crayola marker, black ballpoint pen, ransom note, coffee filter paper, scissors, small plastic cups, drinks of the same color with varying levels of sugar (Powerade, Red Bull, Monster, etc.), Hydrometer, forensic powder (cocoa powder and baby powder), baby oil, poster paper cut into small squares, Q-tips, ink pad, Goldenrod paper, dandelion colored crayons, Windex, rubbing alcohol

What/how to prepare ahead of time:

Secret Note: On a piece of goldenrod paper, write a message in Crayola Dandelion crayon. This message can be revealed with a base, like Windex.

Chromatography paper: Cut coffee filters into rectangles about 3 cm x 5 cm in size. Draw a line in pencil about 1 cm from the bottom.

The mystery drinks: The four mystery drinks are Monster, Redbull, orange Powerade, and approximately 3 plastic spoonfuls of sugar with about 1 cup of water. Red and yellow orange food dye can be used to make all the beverages about the same color. You should prepare two solutions of the sugar-water because one will be given to the class and one will be used at the crime scene.

What Happens/Why: Students will investigate who stole the ice cream machine through a series of four clues: ransom note, drink analysis, fingerprint analysis, and revelation of a secret note. After considering all the clues the students will have to rule out suspects to discover the thief.

The Case: Last night, there was a robbery at Colby College! Somebody stole the ice cream machine out of Foss dining hall. In its place was a note left by the thief. Colby Security currently has four suspects in custody. Each suspect has several different pens in their pocket. Which pen was used to write the note? Use chromatography to figure it out!

Part 1:

Ransom Note:

First, the teacher will cut out a small piece of the ransom note (this should be written on coffee filter paper) and the class with note what happens with the paper is place in a cup with 1 mL of rubbing alcohol. Then, students receive a piece of chromatography paper with a thin pencil about 1 cm from the bottom line on it. Writing on the paper with pencil will not affect the results. Students will place a very small dot of each of other suspects’ pens along the horizontal line about half a pinky’s width apart. Remember which one is which! You can do this by labeling each dot with pencil.

Once all the dots are in a line, carefully lower the paper into the small plastic cup full of 1 mL of rubbing alcohol. Put this aside for now.

Due to polarity, the different inks will be drawn up the piece of paper, leaving different streams of color. The permanent marker—which belonged to the thief—will be significantly more purple than the other inks, making it easy to identify.

Chromatography works because the different compounds within the ink of each marker have different polarities. When the paper is placed into the rubbing alcohol solvent, the solvent is drawn up the paper. It will “attract and drag” the polar substance within the ink up to paper with it. Since the different compounds within the ink have different polarities, they will be revealed in different stages along the water’s path. The most polar compound will be close to the top of the paper while the least polar will remain near the bottom.

Part 2:

Testing the Mysterious Drinks

Story: The thief left behind an unmarked water bottle with a mysterious orange drink at the scene of the crime. The suspects in custody each have an orange beverage that they often drink. The police can identify the thief based on whose drink matches the drink found at the crime. The orange beverages are Monster, Redbull, orange Powerade, and water with 3 tablespoon of sugar in it and food dye. Each of these substances will have a different sugar level.

To measure the sugar level, we will use a hydrometer. The class will test the sugar content of each drink one at a time. To do this, pour the drink into the provided cylinder. Then place the hydrometer into the solution and spin it. When the hydrometer comes to a rest, read the measurement that marks where the meniscus of the liquid sits. The higher the number, the more sugar there is in the drink. There should be 5 substances. 1-4 should all be different but the 5th one is the thief’s and it should be a repeat of any of the substances.

Part 3:

Dusting for Prints:

Story: As the police are inspecting the water bottle, they realize that the thief left a fingerprint on it! It is your job to identify which of the suspects the fingerprint belongs to. However, before looking at the thief’s fingerprint, we will practice looking at our own fingerprints. There are several different types of fingerprints. Look at the figure below to familiarize yourself with the different types.

Next, using a Q-tip, each student will barely coat his or her finger with baby oil. If they apply too much, simply wipe it away with the dry end of the Q-tip. Then have them firmly press their finger on top of a piece of poster paper. Can they see it? Have them gently sprinkle a small amount of forensic powder over the fingerprint. Blow away any excess and then observe it with a magnifying glass. To get a better look, gently put your finger on the inkpad and then carefully make a print on the same piece of paper. Take a look at it with a magnifying glass. What kind of print do you have? Look at your neighbor’s print. Is it different? How so?

Types of Fingerprints:

Part 4:

Secret Message:

Story: The thief left behind a secret message. However, the thief didn’t know that security would go to Colby Chemistry for help! The thief’s note is written on an acid/base indicating paper. How do you think we can reveal the message?

Have the class brainstorm different ways to reveal the message. As it turns out the message is written on base-indicating paper. By spraying the paper with Windex the message will be revealed. Before telling this to the student, give them each a small square of paper and a crayon. Have them write secret messages and try to reveal them.

Sources:

Goldenrod paper can be ordered from:

"Goldenrod Color-Changing Paper." Science Projects Experiments, Educational Toys & Science Toys. Web. 28 Jan. 2014. <http://www.stevespanglerscience.com/goldenrod-color-changing-paper.html>.

Fingerprints:

"Classification of Fingerprints." Classification of Fingerprints. Web. 27 Jan. 2014. <http://shs2.westport.k12.ct.us/forensics/04-fingerprints/classification.htm>.

EVIDENCE BOOK

THE CASE:

Last night, there was a robbery a Colby College! Somebody stole the ice cream machine out of one of Foss dining hall. In its place was a note left by the thief. Colby Security currently has four suspects in custody. Each suspect has several different pens in their pocket. Which pen was used to write the note? Used chromatography to figure it out!

EVIDENCE #1:

The Chemists at Colby have already collected a sample of the pen used to write the note. Observe what happened when the ink of the ransom note was placed in the chromatography cup.

Place a very small dot of each of other suspects’ pens along the horizontal line with the sample dot about half a pinky’s width apart. Remember which one is which! You can label them with pencil.

Now, fill the plastic cup with 1 mL of rubbing alcohol. Then gently place the paper into the small cup. Watch the different inks rise up the paper. Describe what happens to each type of ink. Which one matches the thief’s pen?

PEN / RESULT
THIEF
1
2
3
4

EVIDENCE #2:

The thief left behind an unmarked cup with a mysterious orange drink at the scene of the crime. The suspects in custody each have an orange beverage that they often drink. The police can identify the thief based on whose drink matches the drink found at the crime. Carefully record the level of sugar in each beverage from the measurement on the hydrometer. Make sure to check your labels!

DRINK / SUGAR LEVEL
THIEF
1
2
3
4

EVIDENCE #3

The police are inspecting the cup when they realize that the thief left a fingerprint on it! It is your job to identify which of the suspects the fingerprint belongs to. However, before looking at the thief’s fingerprint, we will practice looking at our own. There are several different types of fingerprints. Look at the figure below to familiarize yourself with the different types.

Using a Q-tip, barely coat your finger with baby oil. If you apply too much, simply wipe it away with the dry end of the Q-tip. Then firmly press your finger on to the shiny side of piece of poster paper. Can you see it?

Try dusting your fingerprint like real forensic analysts do. Gently sprinkle a small amount of forensic powder over the fingerprint. Blow away any excess and then observe it with a magnifying glass.

To get a better look, gently put your finger on the inkpad and then carefully make a print on the same piece of paper. Take a look at it with a magnifying glass. What kind of print do you have? Look at your neighbor’s print. Is it different? How so?

Types of Fingerprints:

EVIDENCE #4:

The thief left behind a secret message. However, the thief didn’t know that security would go to Colby Chemistry for help! Before consulting the experts, how do you think we can reveal the message? Write down your ideas below and try them out on your own paper. Did anything work?

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