Ever wanted to make a super secret message to a friend, like you were a spy in the movies?
In this month's 20 Minute Lab, we'll be writing a message using the "ink" of a common fruit!
Planning to set up a lemonade stand this summer with your friends or family? In between customers, you can use the lemonade to write secret messages to each other!
If you don't have a lemon or lemonade, you can use bottled lemon juice, an orange, lime, other citrus fruit, or even vinegar!
If you could see your message after the paper dried - without applying any heat - you may have used too much lemon juice when writing. Try it again - this time letting the Q-tip rest on the edge of the bowl before writing to let some of the liquid drip off.
If your message does not appear after applying heat, the heat from the light bulb may not be hot enough. Try using a hotter light bulb or try the iron method.
What's going on?
Did your secret message magically appear? Did it turn dark brown? Why did this happen?
Lemon juice is made up of carbon-based compounds, which you applied to the paper with the Q-tip. As you saw, it doesn't have any color at room temperature.
However, heat breaks carbon bonds and sets some of those carbons free from the paper. When that free carbon contacts the oxygen in the air, it turns a brownish color. This process is called oxidation.
Sometimes substances will oxidize without any added heat. Have you ever had apple slices turn brown when they sit out for a while? That's because the carbon-based compounds in the apple oxidized without the need for the extra heat.
Fun trick: to prevent your apples from turning brown, add some lemon juice to them! Lemon is a natural antioxidant which prevents the oxidation process from happening.
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