Hidden Messages

Concept: An acid/base reaction using two different indicators.

Materials:

Half sheet of chromatography paper

Cardboard piece fitted to paper

Phenolphthalein indicator (clear on paper)

Universal indicator (reddish/orange on paper)

0.1 M Sodium Hydroxide solution

Paintbrush/q-tips

Small sponge/cotton balls

Vinegar (acid)

Directions: Glue or tape cardboard to chromatography paper. Paint a secret message or picture on the chromatography paper using the paintbrush/q-tips. Use phenolphthalein on what you want red in the reaction and universal on what you want purple in the reaction. The phenolphthalein will go on clear and the universal will go on orange. Let the paper dry fully. Brush on the sodium hydroxide with the sponge/cotton balls. The colors will appear. If you want, use the vinegar to make the message/picture disappear again.

Introduction: I have a problem. My friend left me this message and said no one else could see it. But I need help; I can't read all of it. Maybe if I use some of this magic solution...Look! I can read it now!

Explanation: The two colors I used in my message are indicators; they tell us when an acid or base shows up. When there is no acid or base, it is called neutral. The paper is neutral/slightly acidic, and phenolphthalein is colorless and universal is reddish/orange when it is neutral.

When a base, such as sodium hydroxide, is applied, in my magic solution, the indicators change colors to show this. In the presence of base from the hydroxide ions, the phenolphthalein goes from clear to red and the universal goes from red/orange to purple.

When an acid is applied, like the vinegar, the indicators change back again. They go back to how they were (clear and reddish). The acid has neutralized the base that was first applied, which is why the indicators go back to their original colors.

Neutralization Reaction:

Vinegar or acetic acid + Sodium Hydroxide ---> Sodium Acetate + Water

HC₂H₃O₂ + NaOH ----> NaC₂H₃O₂ + H₂O

Waste Discard paper, and if used, q-tips and cotton. Rinse sponge.

Disposal: paintbrush, if used.

Reference: Unknown