Invisible Inks Gary Jacobs, University of Kentucky, Center for Applied Energy Research 2540 Research Park Dr., Lexington, KY th grade chemistry experiment

Overview Experiment Objectives Materials Procedure Conclusions General Observations & Helpful Hints Resources

Experiment Objective To learn about how color changes can be made by reacting substances with heat, or with other substances. This is an introduction to chemistry.

Overview This activity is an adaptation of the experiments described in the websites listed on the last slide. This presentation is mainly focused on helpful tips to successfully complete the activities.

Materials Needed Experiment #1Experiment #2Paper (2 sheets) Q-tip (1)Water/baking soda mix Plastic Cup (1)Plastic Cups (2) Lemon Juice (~1 tsp)Q-tip (1) or Paint brush Lamp with Hot BulbCranberry Juice (~1 tsp) Heat Gun Flash Light

Procedure Experiment #1 1. Pour the lemon juice in a cup. 2. Use the Q-tip to write a word on the paper using the lemon juice and let dry. It will be invisible. 3. An adult supervisor will then hold the paper to the hot bulb and observe the appearance of the word. Experiment #2 1.Pour a small amount of baking soda into a cup. 2.Add just enough water to the baking soda to make a paste. 3.Use the Q-tip to write a word on the paper using the baking soda paste and let dry. 4.Dip the paint brush (or Q-tip) into the cranberry juice and paint the juice over the invisible word. The invisible word should become visible.

Conclusions, Experiment 1 The dry lemon juice is the invisible ink and it will react after contact with the light bulb to make dark letters appear. Ask the students for a hypothesis as to what is causing the reaction. The students will reply either “light” or “heat” from the bulb. The instructor will experiment using the hot gun and the flash light and show it is the heat from the bulb that is important. The reaction is a combustion reaction that will leave behind a small amount of ash. Ask for examples of combustion, and explain the importance of combustion reactions in our everyday lives.

Conclusions, Experiment 2 The baking soda mixture is the invisible ink. A color change is produced when the cranberry juice, which is acidic, reacts with the baking soda, which is a base. Discuss examples of acid-base reactions in our everyday lives. For example, we take antacid medication to relieve a stomach ache. The experiments give the students an introduction to chemistry.

General Observations and Helpful Hints Use the maximum wattage light bulb for which the light fixture is rated; this will minimize the time needed to burn the lemon juice. After applying the baking soda (in Experiment #2), give it ample time to dry completely. Otherwise it will smear when the cranberry juice is applied.

Resources for Invisible Inks About chemistry website: nk3.htm (note: all one word) Kidzworld website