Take Home Lab #2

Take Home Lab #2:  Invisible Ink

Question: What chemical makes invisible ink work?

Safety: Do not eat or drink any of the materials. Clean up any spills.

Materials: Students determine what materials to use.

Procedure: One way to make an invisible ink is to write on a piece of paper with the juice from a fruit and let it dry. Then heating it above a toaster or with a hair dryer will make the writing visible. But what chemical in the fruit juice makes the color change? This is what you will attempt to figure out in this activity.

                First, make sure that you can do the demonstration with a liquid known to work. Use a stick or a cotton swab to write something on a piece of scratch paper (do not waste a new piece of paper) with lemon, apple or pineapple juice. If the juice does not come straight from the fruit, be sure to make sure there is real fruit juice in it. Many fruit drinks that you buy in the store do not really have any fruit juice in them.

                Allow the juice to dry until it is invisible. Hold the paper 2 inches above a toaster (holding the edges of the paper so you do not burn yourself, hold it over a lightbulb, or put it 2 inches in front of a hair dryer. Watch for a couple of minutes to see if the invisible ink becomes visible. If it does not, keep trying until you can see it before you start your investigation.

                Now that you can get invisible ink to turn visible, you will try to figure out what is in the liquid you used that made the ink show up when heated. When you have a hypothesis for what chemical it might be, make up a solution of that chemical and test it. For example, if you believe that salt is what turns colors, test some salt water using the same procedure you did for the fruit juice. Try testing other liquids that have similar chemical and different chemicals.

                Keep a list of the liquids that you tested and a description of the results similar to the chart below.  You must test at least four different liquids.

Data Table:

Liquid:	Observations:
Fruit Juice

Post-Lab Questions:

1. Which liquids made successful invisible inks? Which liquids did not?

2. What did the successful liquids all have in them that the unsuccessful liquids did not?

3. What did your experiments tell you is in the fruit juice that makes it a good invisible ink? Explain your thought process as you came to this conclusion. Use statements such as “ Because _____ and _____ happened, I eliminated ________. Because _____ and ______ were successful, I decided to test _____. And because _____ happened, I conclude that the chemical that makes fruit juice work as an invisible ink is _____.”