Invisible Ink Experiment

Overview:

Students will be experiencing how to make invisible ink using sunlight and lemon juice. By doing this experiment they will only need three supplies. Super easy and super cool for any student!

Time: 

20-30 min

Lesson Materials:

*You can use the document in the link below to either: tailor the experiment to your needs or to have a printable version of this lesson plan*

Invisible Ink Experiment Lesson Plan

The plan is editable and printable. Copy the Google Doc in your own drive and make edits or you can just print.

Invisible Ink Experiment Lesson Video:

https://youtu.be/WxJ7wjUaIlg

Learning Objectives:

By the end of this experiment, students will be able to:

  1. Students will be able to observe how lemon juice can make ink using sunlight.
  2. Students will be able to see how impactful sunlight is.
  3. Students will be able to identify that not needing much can make a cool experiment.

Materials Needed:

Materials

  • Lemon Juice
  • Paint Brush/ Q-tip
  • Paper
  • tupperware/ bowl

Heat/sunlight

  • Direct sunlight

Experimental Methods:

  1. Squeeze the lemon juice into the small container. You can use your hands or, if you have any unhealed scratches, a juicier.
  2. Add the water. Stir.
  3. Write your message
  4. Let the “ink” dry.
  5. Use a heat source to decode the secret message.

Expected Experimental Results:

This is what the final should look like. If you look closely it says “Hello”. The more heat the letters will pop out. Don’t forget to let the paper dry before putting it in heat.

Questions to Think About:

Questions

  1. Why is heat important with this experiment?
  2. What materials could you use instead other than q-tips?
  3. Why are lemons so important in this experiment?
  4. What would you predict would happen if we used a different fruit? (for example an orange)

Predictions/Hypotheses:

  1. Without heat for this experiment the experiment would not work because the lemon juice attracts the heat.
  2. Using a paint brush would also work for this experiment.
  3. If we use a different fruit like orange juice instead of lemon juice it would not work because it does not attract heat.

Chemistry:

Invisible ink is used by heat. While the ink is exposed to direct heat like with sunlight, blow dryer, iron, oven and light bulb, the lemon juice acid will make the letter turn a different color and then the message becomes visible. Lemon juice gets absorbed into the paper. The paper is made of cellulose, which is a long connecting chemical made up of sugar (glucose). The lemon juice weakens the connections between the sugars. When the paper is heated the weakened connections between the sugar breaks apart from the main cellulose structure. The sugars turn brown or “caramelize” in the heat source. The small sugar, glucose, caramelized at low temperatures (320F). The big connected structure, cellulose needs a much higher temperature to caramelize so it remains white after heating in the sun. Caramelizing is basically adding oxygen from the air to the sugar.

Society:

During the Revolutionary War invisible ink was used by the Americans to send messages and help defeat the British. Also, fruit oxidizes without heat: apples and pears. Other foods oxidize (caramelize) with heat, such as flan.

Logistics:

STEAM Subjects: 

Chemistry

Science Vocabulary: 

Energy, Heat

References:

Steve spangler science. “Secret message with lemon juice- sick science.” steve spangler science, steve spangker science, https://www.stevespanglerscience.com/lab/experiments/secret-lemon-juice-messages/

Funding:

CSU Internal Funding Sources:

  • IRA (Instructionally Related Activities Fund)
  • Faculty Small Grant

External Funding Sources:

  • Adobe