Looking for a family-fun mystery to solve this Halloween season? Look no further!
In this activity, your family will learn about chromatography by studying how ink has distinctive properties which can be recognized as different colors that separate when it is exposed to water. By studying the patterns of different black washable ink pens or markers, you can match the colors from the test samples to the pattern found from the Cookie Bandit’s note.
Crack the case at home together using real scientific forensic techniques that are easy and fun for everyone.
Activity time: 30 Minutes
Ages: Grades 1-6
Oh, No! A mystery culprit, who calls themselves the Cookie Bandit, has left behind a ransom note after stealing a beloved cookie jar. Their note, which they left on a coffee filter reads,
“If you ever want to get your cookie jar back again, meet me outside with a bag of candy. -The Cookie Bandit” (Or feel free to get creative!)
The case has been narrowed down to five possible suspects. Each of these suspects has a favorite black marker they use, and each marker is a different brand, and thus will have a distinct and unique combination of pigments in it to form the color black.
By separating out these pigments and comparing them to a sample of pigment from the ransom note, you will be able to use chromatography to determine which pen was used to write the note and who the Cookie Bandit is! (It is also fun to take note of how many different colors each ink sample has and what colors they are.)
- 5 different black markers or pens (note that permanent markers, dry erase markers, and some other brands will not be water soluble. Use ‘washable’ ink to be safe!)
- Coffee Filters (or paper towels could work, too)
- A glass or cup with about 0.5 cm of water in it
- Paper towel, pencil, scissors, and tape
- Write the Cookie Bandit’s note on a coffee filter with one of the 5 markers or pens. Write the note so that there is about 3 fingers of white space from the edge, this will allow the filter to absorb water. Be sure the ink is completely dry for best results.
- Cut coffee filters into 5 strips per participant at about an inch or so wide.
- Three fingers up from the bottom, draw a line across the strips – one pen/marker on each of the strips. Label each strip with a pencil on the top, so you know which strip has a marking from which pen.
- Make a numbered list of which pen correlates to which number, and give each pen sample a name for their owner.
- Harry: Buyartosh – deep blue, black brown, pink
- Zayn: Mozart Brush pen – deep blue/grey, black
- Louis: Tombow AB – indigo, pink, brown, blue, purple
- Niall: Papermate – peach, navy, pink, purple, indigo
- Liam: Stained – black, brown, blue
- Cut a strip of the ransom letter out to test. It should have three finger widths of white space before writing begins, and some space after text, so there is room for the chromatogram, just like with the test samples.
- Tape samples into a cup of 0.5cm of water so that the bottom dips into the water, but it does not hit the ink line. (Depending on the cup used, you can do them all at once, or one at a time).
- Let the strips sit for 1-4 minutes while the water begins to creep up the coffee filter and let it grow until it is about 1 cm away from the top of the taped strip.
- Carefully remove the strips and lay down near the list or on a paper towel and allow for them to dry. [The chromatogram from the ransom note will not be as distinct as the chromatograms from the black lines; the colors should still be distinguishable, so that the pen that wrote the note can be identified].
- Once all your strips, and the strip of ransom note have been tested, compare your ransom note section to the five test strips and see which one matches the ink on your ransom note! That’s your culprit!
So, what is expected to happen?
The particles of color in ink are suspended in or dissolved in a liquid base. When you write, that liquid base dries up, leaving just the color particles behind. When you dip the bottom strip in water, the liquid creeps up the filter and contacts that dried color from the ink. The particles are dissolved again and wicked up the strip with the water.
How does this work?
This ‘rehydration’ of the color and the way it wicks up with the water is a specific term called capillary action. The more water soluble a molecule is, the farther the color particle will be carried upward and the higher it will end up on the strip of paper. In other words, the color particles are attracted to both the water and the filter paper. Each and every color has a different solubility, or a different and varying level of attraction to water and the filter. Thus, less soluble colors would be more attracted to the filter paper than the water, and may not move much higher on the strip of paper at all. Depending on the relative attraction of a dye to the water and the paper, a color will travel at its own rate. The differing rates of travel is key to separating out the colors in the black ink.
This is chromatography: the separation of a mixture by passing it in solution or suspension through a medium in which the components move at different rates.
Need some further explanation? Check out this video.
Were you able to identify the pen that matched the ransom note?
Who stole the cookie jar? For me, it was Louis!
Let us know who YOUR cookie bandit was on social media.
Don’t forget to tag JMF!
Blog written and researched by Lauren Maley, JMF Development Associate