Invisible Inks 4th grade chemistry experiment G ary Jacobs, jacobs@ caer.uky.edu University of Kentucky, Center for Applied Energy Research 2540 Research Park D r., Lexington, KY 40511 8592570276
Overview • Experiment Objectives• M aterials• 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.
M aterials Needed Experiment #1 Experiment #2 Paper (2 sheets) Paper (2 sheets) Qtip (1) W ater/baking soda mix Plastic Cup (1) Plastic Cups (2) Lemon Juice (~1 tsp) Qtip (1) or Paint brush Lamp with Hot Bulb Cranberry Juice (~1 tsp) Heat GunFlash Light
Procedure Experim ent #11. Pour the lem on juice in a cup.2. U se the Q tip to write a w ord on the paper using the lem on juice and let dry. It w il be invisible. 3. An adult supervisor w il then hold the paper to the hot bulb and observe the appearance of the w ord. Experim ent #21. Pour a sm al am ount of baking soda into a cup.2. Add just enough w ater to the baking soda to m ake a paste.3. U se the Q tip to write a word on the paper using the baking soda paste and let dry. 4. D ip the paint brush (or Q tip) into the cranberry juice and paint the juice over the invisible word. The invisible w ord should becom e 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 acidbase 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 • U se 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:http://chemistry.about.com/cs/howtos/ht/invisibleink3.htm (note: al one word) • Kidzworld website http://www.kidzworld.com/site/p3844.htm