by Dr. Kathleen A. Carrado, Argonne National Labs |
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
First, place a raw egg in a 1-pint glass jar with a lid (mason jar, for example). Do NOT crack the egg! Then pour in enough clear, white vinegar (preferably from a newly opened bottle) to cover the egg. Close the lid and check it every once in a while over the next 24 hours. What happens? Bubbles start to form on the egg shell immediately, which increase in number as time goes on.
After 24 hours the shell will be gone (some pieces may be floating). But
the egg remains intact because of a thin membrane, though which the yolk
can be seen. Why? The chemical in vinegar is acetic acid (a weak acid).
Egg shells are made of calcium carbonate, another chemical compound.
When these two substances react, carbon dioxide bubbles form from the
carbonate and the egg shell disappears.
First put a few raisins in the water. What happens? They sink. Why?
The raisins are heavier and more dense than water. Now put a few raisins
in the soda. This time they should also sink, but then gas bubbles of
carbon dioxide will stick to the raisin and eventually lift it with them to
the top. Then what? The bubbles pop and the raisins sink again,
whereupon its "dance" can continue! Now, what does this tell you about
how a life jacket works?
Place 1/2 cup skim milk in a glass or jar. Add 1/8 cup vinegar and stir
for a few minutes. Small lumps, which are curds, will form. Let them
settle for a few minutes, then pour off as much liquid (the "whey") as
possible. Filter the remainder through a cheesecloth until the curds are
dry, and return them to the glass. Add about 1/2 teaspoon baking soda
(for neutralization) to the curds, and mix. If the glue is too thick add a
few drops of water. Now test your glue with a few pieces of paper.
Notes: The process of separating curds from whey is very similar to the
making of cottage cheese. Do not save the glue. Wash up with water.
Whole milk will not work because the fat molecules precipitate with the
casein and interfere with the glue structure, making it too weak.
A long time ago chemists discovered how to make good dyes from coal
tar, and the FDA has certified four - one blue, two reds, and one yellow -
as safe to eat. This experiment will let you detect coal tar dyes in food.
You'll need colored liquids like tomato or beet juice, soda, tea,
maraschino cherries, grenadine, jellies, water from canned and cooked
vegetables; powders like paprika, saffron, or turmeric in 1/2 cup water.
Also, a small enamel or steel saucepan (aluminum pans won't work!),
vinegar (acetic acid), and white wool yard (not acrylic).
Put some of a colored liquid, a few drops of vinegar and a 3-inch piece
of the yarn into the pan and heat to boiling. Make sure that an adult is
there to supervise this step. Lift out the yarn with a fork and rinse it in
cold water. If the yarn is colored (dyed) after this boiling step, then the
colored liquid contains an artificial dye made from coal tar.
The protein in wool reacts with coal tar dyes in an acid environment
(vinegar) to form a new stable substance via chemical bonding. Natural
dyes do not form this bond with the wool and easily wash away with hot
water. Now check your results against the food labels.
Experiment #2. One of our sources tells us that Coca Cola contains only traces of extracts from the coca plant and the kola nut. In this
experiment you can come pretty close to making one of the most closely
guarded of all trade secrets - the formula for Coke. Mix well in a glass:
1 tablespoon + 1 teaspoon sugar, 1 teaspoon vanilla extract, 1/2 teaspoon
bottled lime juice, 1/2 cup club soda, and a sprinkle of cinnamon. Close
your eyes and give it a try, you might be surprised! This mixture will look
very different from real colas because there are no artificial colors
added yet. Experiment with the amounts of the ingredients a little bit to
get the taste just right. Bon Appetit!
Procedure:
- pour 1/2 cup water into the bowl
- add 10 drops of iodine to the water and stir
- squeeze the juice of the lemon into the cup
- cut out a smaller-than-bowl-sized section of paper
- dip the art brush into the lemon juice and write a message on the
paper
- let the juice dry on the paper
- put the paper in the iodine solution in the bowl
What happens? The paper should turn a blue-purple color everywhere
except where the message was written, so that the words are outlined by
a dark background. Why? When starch molecules in the paper combine
with iodine, the combination is blue-purple in color. But Vitamin C (from
the lemon) combines with iodine to form a colorless molecule. The area
covered with lemon juice remains unchanged in color because of this.
Fill the saucer with water, but only enough so that the water line is
below your pen lines. Place the rounded edge of the cone in the water and
let it sit for about 10 minutes. If there was too much water (above the
ink lines) it will just wash off the ink. Let the water rise on the paper
until it reaches about an inch from the tip of the cone. Then take it off
the saucer and let it air dry.
A trail of color (purple, orange, pink, and yellow for an Expresso marker
pen) should be separated from the black ink, while the green ink should
make a trail of blue and yellow. This happens because black and green are
combinations of many other colors. As the water rises on the paper, the
ink dissolves in it. The colors separate and rise to different heights
because of differences in the chemicals producing the color. The
lighter-weight chemicals will move the fastest, which means that they
will move with the water to the top of the paper.
At first the liquid should be milky white and opaque. Opaque means that
light cannot pass through, making the solution impossible to see through.
The milky appearance is due to undissolved particles of lime that are
temporarily suspended in the water. It takes time for all of these
particles to settle down. The resulting clear liquid contains as much
dissolved lime as it can hold before settling out. This is called a
saturated solution. It is similar to dissolving Kool-Aid or lemonade
crystals in water. When too many crystals are used, the extra settles out
on the bottom.
The jar must be kept tightly closed so that carbon dioxide from the air
won't dissolve in it. We have other plans for this solution.
Kids, would you like to make your own "dancing California raisins" by
using chemistry? All you need are two clear plastic cups, one filled with
water and the other filled with a cold, clear soda like 7-Up. And raisins
of course.
Kids, how would you like to turn your nice shiny copper-colored pennies
into green ones? All you need is a saucer, a paper towel, vinegar, and 3-5
pennies. Fold the paper towel in half and then in half again to make a
square. Put in on the saucer. Pour over enough vinegar to wet the towel,
then place the pennies on top of the wet towel. Wait for 24 hours
and.....what happens? The tops of the pennies should turn green. Why?
Vinegar is a dilute solution of the chemical called acetic acid. The
acetate part of this acid combines with the copper of the pennies to form
the green coating, which is copper acetate.
Kids, what do Little Miss Muffet's curds & whey have in common with
glue? Just what is a curd, anyway? Curds are a milk protein called
casein (a natural organic polymer) which actually has a lot of industrial
uses. One of them is a key ingredient in Elmer's Glue-All. In Operation
Glue, YOU can produce glue from milk using ordinary household products.
Kids, did you know that most of the natural color of convenience foods is
lost during processing? Food manufacturers add artificial coloring to
foods to restore their expected color. Red food dyes are added to hotdogs
that would otherwise look gray, for example. Natural food colorings
(pigments from paprika, beets, carrots, and leaves) fade with time and
generally have a low coloring power.
Experiment #1. Kids, imagine a cooler filled with cans of soda at a
summer picnic. Did you ever notice that all the diet soda cans float on
top of the ice-cold water, while the rest have to be fished out from the
bottom? You can see this for yourself if you have a can each of a regular
and diet soda. Put them in a large container of water like an aquarium, a
cooler, or even the bathtub. Both cans are the same size but they weight
different amounts because of the extra 2/3 ounce of sugar in the regular
soda. It is enough to make the heavier one sink and the lighter one float
on water. The cans differ in their "density", which is the amount of mass
in a certain size. Mass is the amount of matter in a body (an astronaut
weighs less on the moon but has the same mass as on earth).
Kids, let's try to write a message that will appear as if by magic on
paper, using chemistry. You will need a soup bowl, some tincture of
iodine, a lemon, some notebook paper, a cup, and an art paintbrush.
Kids, here we will separate the colors in ink and make a rainbow effect.
You will need green and black water-soluble marker pens, a cone-shaped
coffee filter (for Melitta coffeemakers), a saucer, and water. Regular
coffee filters are too wrinkled and thin to work well. About 1/2 inch
above the rounded edge of the flat, cone-shaped filter, make a thick, dark
green line about one inch long parallel to the edge. Do the same with the
black marker about one inch away from the green mark. You can do the
same on the other side of the cone if you like. Pull out the filter so that
you have a shape like an upside-down ice cream cone.
Part I. Limewater
Kids, here you will make a solution that can test for the presence of
carbon dioxide (CO2 ) gas. This is a two-part project. Save the limewater
you make for use in the next issue of ChemShorts. You will need two
glass quart jars with lids, a tablespoon, and lime (CaO, the substance
used in making pickles, not the small green citrus fruit). Fill one jar
with water. Add one tablespoon of lime and stir. Secure the lid and allow
the solution to stand overnight. Pour off the clear liquid into the second
jar very carefully, do not let any of the settled lime sneak in. Keep the
jar of clear limewater closed until needed.