Activity 3 OOperationOOperationppeerraattiioonn EEspionageEEspionagessppiioonnaaggee Kids test for the best way to make invisible reveal itself. They discover that mixing a (invisible ink made from baking soda) and an (fruit juice) can create a . In this case, the chemical reaction causes a change in color, making the invisible message appear.

Materials • Activity sheet for each kid • 1 box of baking soda (1 tsp. per kid) Prepare Ahead Lead the Activity • Water Familiarize yourself with the activity, which happens 1 Introduce Ruff’s challenge. (5 minutes) • Juices: cranberry and purple grape in three stages: Hand out the activity sheets. Tell kids they’ll be juices; grape juice concentrate 1. Writing messages with invisible ink making invisible ink and writing secret messages with • Sticky notes to label juices it. Later, they’ll make their hidden messages appear! • Bowls (see “Prepare Ahead”) 2. Having a group discussion about , bases, • Red and blue food coloring and chemical reactions while the messages dry • Measuring spoons 2 Write with invisible ink. (15 minutes) Have • spoons (1 per kid) 3. Testing out different ways to reveal the message kids follow the directions for writing with invisible ink • Cotton swabs (2 per kid) (steps 2 and 3 on the activity sheet). When they’ve • Cotton balls (6 per kid) • Set up tables for the fi rst stage. Each kid needs a cup fi nished, have them leave their papers to dry, which • Cups (1 per kid) with a tsp. of baking soda, a spoon, a couple of cotton will take about 10 minutes. • Paper (1 sheet per kid) swabs, and a piece of paper. Place paper towels and a • Paper towels (1 roll per table) bowl of water in the center of each table. • Chart paper and marker 3 Discuss acids and bases. (5 minutes) Tell kids • Prepare and set aside materials for the third stage. that to make their messages appear, it helps to know National Science Education Standards Each table will need: three bowls fi lled halfway, one a little chemistry. Draw the pH scale (left) on chart

Grades K–4 TM/© 2008 WGBH Educational Foundation. each with grape juice, grape juice concentrate, and paper. Explain that acids and bases are common Science as Inquiry: abilities necessary to cranberry juice; one bowl fi lled halfway with water chemicals, and give a few examples. (Citrus juices and do scientifi c inquiry; understanding plus a few drops of red and blue food coloring (so it about scientifi c inquiry vinegar are acids; baking soda, borax, , and Physical Science: properties of objects looks like juice). Label the bowls with sticky notes. other cleaners are bases.) and materials Also set up a bowl fi lled with cotton balls, and an Grades 5–8 empty bowl for the used cotton balls. The pH scale indicates how acidic or basic a substance Science as Inquiry: abilities necessary to is: the scale goes from O (most acidic) to 14 (most do scientifi c inquiry Z2 =MKVO basic). Acids and bases are chemical opposites, and Physical Science: properties and changes when they are combined, a chemical reaction can of properties in matter 0714occur. Some signs of a chemical reaction include Acid Base foaming, fi zzing, or a change in color. Tell kids to ,K^^O\c 6OWYX @SXOQK\ :_\O ,KUSXQ ,Y\Kb 6S[_SN watch for a chemical reaction as they try to reveal the +MSN 4_SMO  AK^O\ =YNK #  .\KSX invisible message. "  ! " -VOKXO\  Indicates how acidic or basic a subtance is 13 4 Make predictions. (5 minutes) Ask kids: 7 Discuss what happened. (10 minutes) 8 Award Points. (5 minutes) Time to rack up • Looking at the pH scale, is baking soda a base • Ask kids what worked best to reveal the secret some points! Review the activity’s key ideas by or an acid? (A base) message. (Grape juice concentrate) asking the following questions, worth 50 • If you wanted to create a chemical reaction with • Is this what they predicted? (Answers will vary.) points each: • What does a pH scale show? (How acidic or the baking soda, what would you combine it • Did any of the other liquids work ? (A faint basic a substance is) with, a base or an acid? (Its opposite, an acid) message appeared with the grape juice.) • Is baking soda a base or an acid? (A base) • Of the four liquids you’re going to use to reveal • What kind of chemical reaction did they see? your messages (grape juice, grape juice (A change in color. The grape juice concentrate • What about the juice? (An acid) concentrate, cranberry juice, and colored turned a bluish-green color.) • When you mix a base and an acid together, water), which one do you think will work best? • Why do you think the grape juice concentrate what can happen? (A chemical reaction) Why? (Record predictions on chart paper.) might have worked better than the other • What kind of chemical reaction occurred here? • What kind of chemical reaction do you think juices? (Answers will vary. Kids may say it has (A color change) you’ll see? Some choices are: foaming, fi zzing, something to do with being a concentrate, or a change in color. which is correct.) Tell kids that grape juice contains a pigment, which gives it its color. 5 Set up materials for revealing The acid–base reaction between the baking the invisible ink. (2 minutes) Prepare soda and grape juice caused a color change, tables for the third stage, as outlined in and the amount of pigment in the grape juice “Prepare Ahead.” infl uenced how dark the message became. Because grape juice concentrate has more 6 Test the different liquids and pigment in it than grape juice does, it make observations. (15 minutes) Have produces a darker, more visible message. kids follow step 4 on the activity sheet. Make sure they use a different liquid on each section of their paper, as well as fresh cotton balls. Have them pat the liquids sparingly over each section so their paper stays as dry as possible. If time permits, have kids create additional secret messages, trade them with others, and then reveal them.

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