The Case of the Terrible T. Rex by Michele Torrey Read Free Book Online

determine what caused the bag (tent) to float. Werewolves? Hot air? Hmm … jot your conclusions in your lab notebook.

    How does this work?
    Air is composed of molecules. When air is cold, the molecules are close together and vibrate very little, making cold air dense and heavy.

    In hot air, however, the molecules vibrate quickly, bumping into one another like popping corn. Because each molecule needs more space to move, hot air expands, making hot air lighter and less dense than cold air.

    Conclusion? Hot air tents are lighter than the surrounding cold air environment, so they float up, up, and away! (FYI: Werewolves, besides being shifty and dangerous creatures, are quite dense and therefore must stay on the ground.)

I t’s tragic, quite tragic indeed. The water is polluted. The fish are counting on you to save the day! In this activity, you will test the pH of various water samples, just like Nell did. You will determine which water is safe for the fish and which water needs to be cleaned up, pronto!
    MATERIALS
    •   4 large baby-food jars with lids

    •   masking tape

    •   permanent marker

    •   measuring spoons

    •   tap water
    •   white vinegar
    •   baking soda
    •   water from a local river, stream, or lake
    •   purple cabbage
    •   pitcher
    •   measuring cup

    •   white coffee filters
    •   coffee strainer

    •   1-quart jar with lid
    •   pencil

    •   scissors

    •   tweezers

    •   2 clean, dry plates
    PROCEDURE
    1.    Collect and prepare four water samples for testing. Prepare each sample as follows (using the tape and marker, label the jars clearly with numbers 1 through 4, and replace the lids as you go):

    a)    Jar #1: fill with tap water to about ¼ inch from the top.
    b)    Jar #2: pour in 1 tablespoon of white vinegar, then fill with tap water to about ¼ inch from the top.
    c)    Jar #3: fill halfway with tap water, add 1 teaspoon of baking soda, replace lid, and shake until dissolved. Finish filling with tap water to about ¼ inch from the top.
    d)    Jar #4: take a sample from a local river, stream, or lake. (See “Good Science Tip” on page 69.) Fill the jar to ¼ inch from the top.
    2.    Ask an adult to dice about 3 cups of cabbage. Place the cabbage in a pitcher and ask an adult to pour approximately 1½ cups of boiling water over the cabbage, enough to cover it completely. Let it soak for 30 minutes. (Note: cabbage juice can stain, so wear a lab coat!)
    3.    Place one coffee filter into the coffee strainer. Over a sink, pour the cabbage juice through the coffee filter/strainer into the 1-quart jar. (Be careful that clumps of cabbage don’t fall—SPLAT!—into the strainer and stain your clothes!)

    4.    With the lid off the jar, let the juice cool completely. Once cool, replace the lid. Using a tape and marker, label the jar “Cabbage Juice,” and date it. ( NOTE: keep it refrigerated and discard after twenty-four hours.)
    5.    Draw some fish on white coffee filters. Each fish should be about 2 inches long. You’ll need at least four fish, but make extra just in case. (Topnotch scientists are always prepared.) Cut out the fish with scissors.

    6.    Using the tweezers, dunk one fish completely into the cabbage juice, and then place the wet fish on a plate to dry. Repeat with each fish. Allow fish to dry thoroughly.

    7.    Using a pencil, now label your four (dry) fish “#1,” “#2,” “#3,” and “#4.”

    8.    Again using the tweezers, dip the #1 fish into the #1 water sample. Lay the wet fish on another clean plate. Dip the #2 fish into the #2 water sample, and so on.
    9.    Important: record your results while the fish are still wet.

    How Does This Work? (Reading the Results)
    Scientists created the pH scale as a measurement of whether a substance is an acid or a base. The pH scale is numbered from 1 to 14. Acids range from 1 to 6. Bases range from 8 to