• INVISIBLE INK

     

    Sometimes people tell me they can't do any science projects because they don't have any chemicals. There are some activities that don't require any chemicals you don't already have. A great example is invisible ink.

    Invisible ink is any substance that you can use to write a message that is invisible until the ink is revealed. You use the ink by writing your message with it using a cotton swab, dampened finger, fountain pen, or toothpick. Let the message dry. You may want to write a normal message on the paper so that it doesn't appear to be blank and meaningless. If you write a cover message, use a ballpoint pen, pencil, or crayon, since fountain pen ink could run into your invisible ink. Avoid using lined paper to write your invisible message, for the same reason.

    How you reveal the message depends on the ink you used. Most invisible inks are made visible by heating the paper. Ironing the paper or holding it over a 100-watt bulb are easy ways to reveal these types of messages. Some messages are developed by spraying or wiping the paper with a second chemical. Other messages are revealed by shining an ultraviolet light on the paper.

    Make Invisible Ink

    Anyone can write an invisible message, assuming you have paper, because body fluids can be used as invisible ink. If you don't feel like collecting urine, here are some alternatives:

    Heat-Activated Invisible Inks
    Iron the paper, set it on a radiator, place it in an oven (set lower than 450¡ã F), hold it up to a hot light bulb.

    ¡¤         any acidic fruit juice (e.g., lemon, apple, or orange juice)

    ¡¤         onion juice

    ¡¤         baking soda (sodium bicarbonate)

    ¡¤         vinegar

    ¡¤         white wine

    ¡¤         dilute cola

    ¡¤         diluted honey

    ¡¤         milk

    ¡¤         soapy water

    ¡¤         sucrose (table sugar) solution

    ¡¤         urine

    Inks Developed by Chemical Reactions
    These inks are sneakier, because you have to know how to reveal them. Most of them work using pH indicators, so when it doubt, paint or spray a suspected message with a base (like sodium carbonate solution) or an acid (like lemon juice). Some of these inks will reveal their message when heated (e.g., vinegar).

    ¡¤         phenolphthalein (pH indicator), developed by ammonia fumes or sodium carbonate (or another base)

    ¡¤         thymolphthalein, developed by ammonia fumes or sodium carbonate (or another base)

    ¡¤         vinegar or dilute acetic acid, developed by red cabbage water

    ¡¤         ammonia, developed by red cabbage water

    ¡¤         sodium bicarbonate (baking soda), developed by grape juice

    ¡¤         sodium chloride (table salt), developed by silver nitrate

    ¡¤         copper sulfate, developed by sodium iodide, sodium carbonate, potassium ferricyanide, or ammonium hydroxide

    ¡¤         lead(II) nitrate, developed by sodium iodide

    ¡¤         iron sulfate, developed by sodium carbonate, sodium sulfide, or potassium ferricyanide

    ¡¤         cobalt chloride, developed by potassium ferricyanide

    ¡¤         starch (e.g., corn starch or potato starch), developed by iodine solution

    ¡¤         lemon juice, developed by iodine solution

    Inks Developed by Ultraviolet Light (Black Light)
    Most of the inks that become visible when you shine a black light on them also would become visible if you heated the paper. Glow-in-the-dark stuff is still cool. Here are some chemicals to try:

    ¡¤         dilute laundry detergent (the bluing agent glows)

    ¡¤         body fluids

    ¡¤         tonic water (quinine glows)

    ¡¤         vitamin B-12 dissolved in vinegar

    Any chemical that weakens the structure of paper can be used as an invisible ink, so you might find it fun to discover other inks around your home or lab.

     

    INVISIBLE INK FROM LEMON JUICE

     

    Lemon juice is acidic and weakens paper. When paper is heated, the remaining acid turns the writing brown before discoloring the paper.

    Difficulty: Easy

    Time Required: A Few Minutes

    Here's How:

    1.      Squeeze lemons to obtain their juice or obtain bottled lemon juice.

    2.      Use the juice as 'ink' by applying it to a stick or paintbrush and writing on paper.

    3.      Allow the paper to dry.

    4.      When you are ready to read your invisible message, hold the paper up to sunlight, a lightbulb (recommended), or other heat source.

    5.      The heat will cause the writing to darken to a pale brown, so your message can now be read.

    6.      Another way to read the message is to put salt on the drying 'ink'. After a minute, wipe the salt off and color over the paper with a wax crayon to reveal the message.

    Tips:

    1.      Experiment with other juices. White wine, orange juice, vinegar, and apple juice all work well, too.

    2.      A cotton swab makes an excellent disposable 'paintbrush'.

    3.      The writing turns brown because the weakened paper burns before the rest of the paper. Be careful not to overdo your heating and ignite the paper!

    What You Need:

    ¡¤         Lemon or Lemon Juice

    ¡¤         Sunlight or Heat Source

    ¡¤         Paper

    ¡¤         Paintbrush or Stick

    PEPPER AND WATER CHEMISTRY TRICK

     

    The pepper and water science trick is one of the easiest magic tricks you can perform. Here's how to do the trick and an explanation of how it works.

    Materials for the Pepper & Water Trick

    You only need a few common kitchen ingredients to perform this science magic trick.

    ¡¤         black pepper

    ¡¤         water

    ¡¤         dishwashing liquid

    ¡¤         plate or bowl

    Performing the Pepper & Water Trick

    1.      Pour water into a plate or bowl.

    2.      Shake some pepper onto the water.

    3.      If you dip your finger into the pepper and water, nothing much happens.

    4.      If you put a drop of dishwashing liquid on your finger and then dip it into the pepper and water the pepper will rush to the outer edges of the dish. If you are doing this as a 'trick' then you might have one finger that is clean and another finger that you dipped in detergent before performing the trick.

    How the Pepper & Water Trick Works

    When you add detergent to water the surface tension of the water is lowered. Water normally bulges up a bit, like what you see when you look at a water drop. When the surface tension is lowered, the water wants to spread out. As the water flattens on the dish, the pepper that is floating on top of the water is carried to the outer edge of the plate as if by magic.

     

    HOW CAKES ARE MADE

    In order for a cake to rise, it must have a leavening agent to make the batter increase in volume. Most of the cakes use carbon dioxide, which is released from the baking soda or baking powder in the recipe. This carbon dioxide needs a place to go, so that¡¯s where the sugar comes in.
    The first step in making a pound cake is to take a fat, such as butter or shortening, or a combination of the two, and beat it with an electric mixer. This incorporates air bubbles. Then, sugar is sprinkled slowly into the butter. As the sharp sugar crystals cut into the butter, tiny pockets are formed and fill with air as the mixer blades pull more butter over the top of the hole to close it. This makes the butter double in volume and become creamy in texture, which is why this procedure is called ¡°creaming.¡± If the crystals of the store brand sugar are smaller than the old favorite, or the edges of the crystals aren¡¯t as sharp, they won¡¯t cut into the butter as deeply. This makes a smaller hole, so less air can be pulled through. Then, the eggs are usually added, which adds more volume and allows the mixture to hold even more air. The dry ingredients, including the baking soda or powder, are then added, usually alternating with liquid. When the baking soda or powder comes into contact with liquid, carbon dioxide is released. As the batter heats up, bubbles form and the batter rises. As the carbon dioxide breaks down, the moisture in the cake forms steam, which fills the air pockets our sugar made. Eventually, the steam evaporates, but by this time the protein in the flour has had enough time to set, thus making the cake hold its shape.

    Just as heat makes steam and carbon dioxide expand, coolness causes contraction. Open the oven door before the crumb structure is set and a draft will burst the tiny bubbles and the cake will fall.

    One of the most common mistakes in baking cakes is to overbeat the batter after adding the flour. This makes the flour develop too much of the protein gluten, which is what makes the cake hold its shape. If you get too much, the cake will be tough. Alternately, adding one-third of the dry ingredients with one-third of the liquid ingredients until both are blended in seems to make just the right amount of gluten form to make a tender cake. Cake flour is higher in starch and lower in protein than all-purpose flour. It also is ground finer than regular flour, and produces a finer crumb.

    Have your ingredients at room temperature before you start ¡ª butter should be around 65 degrees to cream nicely. Probably a return to Ms. Crawford¡¯s old sugar will solve her pound cake problems. Click the link below for my grandmother¡¯s pound cake recipe. It¡¯s one of the best I¡¯ve ever tasted, although I may be just a tad biased.

    GAK RECIPE

    Ingredients:

    ¡¤  1 cup Elmer's glue

    ¡¤  food coloring, your choice of color (optional: coloring can stain!)

    ¡¤  1 cup liquid starch

    Pour glue and coloring in plastic container.

    Stir until color is thoroughly mixed in.

    Add starch a little at a time, stirring with a spoon or kneading with your fingers as mixture thickens.

    Keep stirring until mixture holds together like putty.

    Test with your fingers: if too sticky, add more starch in small amounts until mass is smooth and rubbery. 

    Oobleck Recipe

    READ THE BOOK BARTHOLOMEW AND THE OOBLECK by Dr. Seuss

    Another interesting substance is called "oobleck." It also acts like a liquid until pressure is applied.

    Ingredients:

    Homemade Glue from Milk

    by Matt Spencer


    Materials: 3 jars, skim milk, vinegar, baking soda, paper towels, coffee filter, paper to test glue, stirring rod

    Age range: 5-10 (kindergarten - fifth grade)

    Introduction

    With this experiment you can make surprisingly good glue from common kitchen items. I started by having my daughter draw pictures of insects of her choosing on a piece of paper. I then had her draw a picture of a landscape with flowers on a second piece of paper. I explained to her that we were going to use special glue to put the insects in the garden.

    Procedure

    1.      Pour about 100 ml (roughly 1 cup) of skim milk into one of the jars.

    2.      Add about 15 ml (roughly 1 tablespoon) of vinegar to the milk.

    3.      Stir the mixture (optional: heat the mixture slowly).

    4.      Cover the top of one of the empty jars with the coffee filter.

    5.      Filter the milk/vinegar mixture by pouring the liquid through the coffee filter.

    6.      Once the liquid has drained, scrape the solid residue from the filter.

    7.      Use paper towels to dry the solid as much as you can, and return the solid to a clean jar.

    8.      Add a small amount of baking soda to the solid. (How much you should use will depend on the amount of solid you have and how well it was dried. Start with about 1/4 teaspoon.)

    9.      Mix and test the resulting glue.

    Leave the remainder of the glue to dry for later observations.

    Observations

    By adding vinegar to milk we produce a solution containing white solids (precipitation), and by filtering the milk we separate the solution into two substances (called curds and whey). The curds can be dried with a paper towel to produce a cheese-like substance.

    The baking soda, when added to the curds, causes them to become a sticky glue. We noted bubbles coming from the solid when the baking soda was added.

    The glue dries to become a plastic-like substance. It has different physical properties than the original milk and vinegar individually.

     


    FOOD CHEMISTRY

    Root Beer Float

    When a scoop of ice cream is added to root beer, the float foams over for essentially the same reason. The surface tension of the root beer is lowered by gums and proteins from the melting ice cream, and the CO2 bubbles expand and release easily, creating a beautiful foam on top.

    Light Up Your Mouth

    All you¡¯ll need for this is some Wintergreen Lifesavers and a dark room. Hand everyone some of the candies and turn out the lights. Stand facing each other, no more than 6 inches apart to see the effect, and begin chewing up the candies. You¡¯ll get to chew with your mouthes open, much to the delight of some kids, to see what¡¯s going on.

    You should be able to see tiny sparks in each other¡¯s mouthes from the chewing. Why? The wintergreen oil in the candies mixed with the sugars in the candies create a small electrical charge from the grinding and chewing. This is called triboluminescence.

    Float Your (Soda) Boat

    If two cans of soda weight the same ammount they should float on water evenly, right? For this you¡¯ll need two unopened cans of soda. one regular and the other diet. You¡¯ll also need a one gallon jug of water to float them in and some markers to track water levels on the jug. Fill the jug up about 2/3 of the way with water and mark where the water sits at. Now add the can of diet soda to the water. Note where the water level rose to and whether or not the can floated. Once you have made the observations remove the can and add the can of regular soda. Mark the water level and whether or not the can floated.

    The can of diet soda should float while the can of regular soda sinks to the bottom. Why? Sugar is more dense than artifical sweetener. So even though the cans have the same volume of liquid their densities are different.

    Deep Sea Diving Raisins

    Did you know that raisins like to deep sea dive? Sure they do! You can watch them as they dive down, pop back up for air, then dive down again. You¡¯ll need a dozen raisins, a clear plastic pitcher, and a bottle of soda water. Fill the pitcher up with the soda water. Then drop in the raisins one at a time. Watch as they happily dive down in the soda water then come back up for air.

    What is really happening is the carbon dioxide gas in the soda water. As the molecules fix themselves to the raisins they make them float up. However once they touch the surface the carbon dioxide is released and the raisins sink back down again, only to repeat the process again.

    Bake That Apple

    Want to teach the kids have to bake their own treats, without buring down the house? Here¡¯s a great one for a sunny day. You¡¯ll need:

    • black construction paper
    • aluminum foil
    • plastic wrap
    • cardboard
    • an apple
    • glue, scissors, tape, toothpicks, and a paper cup

    Cover the cardboard smoothly in the foil and glue it down. Once the glue has dried cut out a large circle of about 5-6¡å diameter. Now cut a smaller circle of the black construction paper, about 2-3¡å diameter. Glue this circle in the center of the foil circle. Once the glue is dry cut a straight line from the outside of this circle to the center then fold it into a cone shape, use the tape to hold it. Push a tooth pick into the center of the cone and stick an apple slice on the toothpick. Cover the top with the plastic wrap and place the entire thing inside a paper cup. Now just set it outside in the sunshine and wait for it to cook.

    The foil reflects the sun¡¯s rays onto the black paper which heats up, the plastic wrap then traps the heat inside. And the poor apple is cooked.

    Taste Testing Ice Cream

    Who would resist the chance to compare ice cream in the name of science? Oh science, why do you have to be so fattening? For this little experiment your kids will get to make their own ice cream, then compare it to some store bought and see what differences they notice. Caramel, nuts, and sprinkles optional. To make your own ice cream you¡¯ll need:

    • rock salt
    • crushed ice
    • 1 cup milk
    • 1 tsp vanilla
    • 1 cup sugar
    • 1 cup whipping cream
    • empty and clean 3 lb coffee can with lid
    • empty and clean 1 lb coffee can with lid
    • wire whisk and tape

    Mix the milk, vanilla, sugar, and whipping cream in the small coffee can. Put the lid on and tape it shut to prevent any leaks. in the larger can put a layer of the ice and rock salt on the bottom, then sit the smaller can inside. Fill up the rest of the larger can with ice and rock salt, then place the lid on top and tape it shut. You want to make sure there won¡¯t be any leaks coming out of the can. Lay the coffee cans down on the floor on their side and let your kids spend the next 15-20 minutes rolling them back and forth. Check the center can occasionally to note it¡¯s change.

    When the ice cream is ready scoop it up and serve it in bowls next to the store bought ice cream. Be sure to label which bowls are the homemade and which are the store bought ones. Let your kids compare the tastes, textures, thickness, and even color of the different ice creams. Look at the ingredients found in each one. Which kind tastes better, which one sounds better for you?

    See how yummy science can be? I love the educational value of every day treats. It makes you think what other lessons can be found in your grocery store¡¯s aisles.