Who stole my phone?

Who stole my phone?

Spy science!

Have you ever wanted to be a detective or a spy? Try this experiment and see if you've got what it takes!

What you need:

  • Different types of felt tip pens
  • Jam jar
  • Water
  • Paper clips
  • Friends and family
  • Kitchen towel or other absorbent paper
  • Scissors
  • Something that your friends and family can steal - how about your phone?

How to:

1. Give your friends and family a pen and a piece of kitchen towel each.


2. Tell your friends and family that you're leaving your phone somewhere in the house (don't leave it anywhere where strangers could take it). Ask your friends and family to decide which one of them will steal it. The thief has to take your phone and leave a ransom note on the kitchen towel with the pen that you gave them. Make sure you don't know who has taken the phone!


3. Return to the crime scene a few hours later. Is your phone gone? Is there a ransom note? If there is, you can investigate the crime!


4. Gather all the pens as evidence. Make sure you know which person had each pen. You're going to compare ink from the pens to the ink in the ransom note.

5. Cut the ransom note into 3cm strips.


6. Cut 3cm strips from a fresh piece of paper towel. With the first pen, draw a small circle on a clean strip of paper. Repeat with a new strip of paper for each pen you have.

7. Fill a jam jar with water. Use paper clips to attach some of the paper strips from the ransom note to the edge of the jar. Dip the bottom of the paper strip in the water, but make sure the water doesn't touch the ink.

8. Use more paper clips to attach the strips of paper with felt tip pen circles to the edge of the jar. Dip the bottom of the papers in the jar, but make sure the water doesn't touch the ink circles.

9. Over the next hour, the water will rise up the paper. What can you see?

The ink from each type of pen will separate into patterns of different colours. Do any of the colour patterns match? Compare the ink pattern from the ransom note to the pattern of each pen. That's the thief!

What's going on?

Felt tip ink is made up of different types of molecules. Each different pen is made up of different combinations of molecules. When you dip the paper into the water, the water travels up the paper.

The water dissolves the ink spots. Ink molecules travel with the water as it continues up the paper. The most water-soluble ink molecules are carried towards the top of the paper. Less water-soluble ink molecules don't travel as far. This forms the ink patterns you can see.

This technique is called chromatography. Real forensic scientists use it to solve crimes.

You can match the ink pattern from the ransom note to one of the pens. The person with that pen is the thief!

Curriculum information

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