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.
Yeast cells digest food to grow. Their favorite food is sugar, either
sucrose (cane sugar), fructose and glucose (from honey, molasses, and fruit)
and maltose (from starch in flour). Glucose is C6H12O6. This fermentation
process makes carbon dioxide and ethyl alcohol. Flour Facts: When mixed
with liquid and kneaded, flour develops enough gluten to support the carbon
dioxide made by the yeast. Gluten is the elastic molecule formed when the
protein of flour meets a liquid. Kneading makes the gluten stronger so it
can hold in the gases formed by the yeast. This recipe didnıt call for
kneading, but many do. After baking the dough youıll see the remains of the
CO2 gas bubbles as air pockets in the bread. Fat Fact: Fats like butter,
margarine, and oil are used in breads to make the gluten strands slippery so
the yeast gases can expand easier. Liquid Facts: Breads made with water
will have a more open texture, a more wheaty flavor, and a crispier crust.
Milk creates breads that are richer with softer texture; crusts are softer
and will brown faster due to the sugar and butterfat in milk. Sugar Facts:
Sugar provides food for the yeast to grow and adds flavor. Salt Fact: Salt
controls the speed at which the dough rises. In next monthıs column weıll
do more experiments with yeast, so stay tuned!
February, 2001
Is yeast alive? Make a yeast solution using 1/2 cup warm water, 1 tsp
sugar, and 1/4 ounce package active dry yeast. Each day, transfer 1 tsp of
original yeast solution to a solution of 1/2 cup warm water and 1 tsp sugar.
Make another sugar solution and add 1 tsp water daily. Keep a record of
observations for five days. Does the yeast culture continue to multiply
even though it is diluted by the daily transfer?
When flour, sugar, water, and yeast are mixed, what happens? Get two empty
1-liter soda bottles and two balloons. Fill each soda bottle with a 1/4
ounce package active dry yeast, 1 tsp sugar, and 1 cup room temperature
water. In one bottle, add 2 Tbsp all-purpose flour. Secure a balloon on
top of each soda bottle. Record and time what happens to the balloons.
What is the difference between them? Does flour make a difference in the
length of time the fermenation works and why?
What effect does temperature have on the fermentation of yeast? Again get
two empty 1-liter soda bottles and two balloons. Fill each bottle with a
1/4 ounce package active dry yeast, 1 tsp sugar, 2 Tbsp all-purpose flour,
and 1 cup room temperature water. Set one bottle in a vessel with warm
water. Set the other bottle in a vessel with ice water. Secure a balloon
on top of each soda bottle. Observe and record results. What effect does
temperature have on the fermentation of yeast? When was the difference most
noticeable? Read over the last two columns for interesting facts concerning
yeast and they will also help you answer the questions asked here.
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Reference: www.redstaryeast.com ("The Science of Yeast" webpage). For
microscopic photos of budding yeast cells check out:
http://goodquestion.net/beer/info/yeast.html or
www.bath.ac.uk/Departments/BiolBioch/wheals2.html
Baking powder is a combination of baking soda plus a dry acid. When baking
powder is mixed in a batter, the dry acid and the baking soda can react
together and release CO2. Dry acids are certain tartrates, phosphates, or
sulfates. Double-acting powders are the most common. The first "action" is
the release of CO2 when one of the dry acids dissolves in liquid and reacts
with the baking soda. The second "action" is the release of CO2 when the
batter is heated in an oven. This relies on a different acid that dissolves
only at higher temperatures.
EXPERIMENT 1. The purpose here is to determine if CO2 is released when
baking soda and baking powder are added to water. Dissolve 1 tsp baking
soda in one cup of water and 1 tsp baking powder (a double-acting one) in
another cup of water. The baking soda should dissolve without fizzing and
the baking powder should fizz. Why? Note also that the baking soda
dissolves completely but that the baking powder solution is cloudy. Look at
the label and youıll see cornstarch is an ingredient. One possible
explanation is that cornstarch doesn't dissolve. A follow-up experiment
with 1/2 tsp cornstarch a glass of water will confirm this.
EXPERIMENT 2. The purpose here is to determine whether baking soda and
baking powder will fizz when acid is added. So, add 1 tsp of vinegar to the
solutions from Experiment 1. We expect that when the vinegar (acetic acid)
is added, CO2 gas bubbles will be released from the baking soda solution but
not from the baking powder or the control cornstarch solution.
EXPERIMENT 3. The purpose here is to determine whether baking soda and
baking powder solutions will fizz when heated. Prepare one cup of water
each with 1 tsp baking soda, baking powder, and cornstarch. After the
baking powder stops fizzing, ask an adult partner to microwave them all for
1 minute (in microwave safe containers). Only the baking powder solution
should fizz upon heating. In this the other dry acid (probably sodium
aluminum sulfate, or alum) dissolves as the product is heated. As it
dissolves, more is in solution to react with the bicarbonate.
Think about all these reactions occurring the next time someone bakes you a
cake. This is inorganic chemistry in action!
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Reference: http://users.rcn.com/sue.interport/food/bakgsoda.html.
A very appealing and information-loaded site is hosted by
www.miamisci.org. Within their "Education" link is an "On-Line
Educational Resources (SLN)" link to such on-line activities as pH and
"The Atoms Family", which deals with energy concepts. Both feature
highly interactive portraits that are just right for K-5. The
Minnetonka Science Center is loaded with teacher tools and ooey, gooey
recipes for K-5 science (Gak, Oobleck, Slime, even a singing cake).
Start at www.minnetonka.k12.mn.us/science and proceed to "Teacher
Information". This site also contains useful science fair information.
Check out the lesson plans at this science connection:
http://student.biology.arizona.edu/sciconn/. They include density of
cereals, crime scene investigations with paper chromatography, and
oobleck and glurch, all for grades 3 and up. Now that youıve made some
Oobleck, hop to the Jefferson Labs site for ideas on what to do with it:
http://education.jlab.org and click on the "BEAMS" program for grades
6-8 activities. There are also great periodic table and element games
on-line here.
A refresher about atoms, elements and matter is hosted at
www.chem4kids.com. Also provided for an advanced student are sections
on math and chemical reactions. "Project Primary" at
www.owu.edu/~mggrote/pp/chemistry/f_chemistry.html has K-3 activities on
polymers, kitchen chemistry, and liquid nitrogen ice cream. A great
site for minerals, soils, and clays can be found at
http://cms.lanl.gov/K_12.html. Numerous links are summarized as well as
downloadable activities. Wonderful kid sites that contain a lot of
elementary science information, including some on chemistry, are Bill
Nye's (BillNye.com), Beakman & Jax (www.beakman.com) and Marshall
Brain's (www.howstuffworks.com, see the Chemistry link).
This is all hard to imagine, so here we describe an experiment testing a
simple membrane model. In dialysis, small molecules pass through a membrane
by diffusion. Itıs like dust blowing through a screen window while keeping
bugs out. Diffusion also predicts which direction the molecules will move,
which is from more concentrated to more dilute areas. Here a plastic bag
will be the membrane. Iodine, starch, and water are the molecules. Starch
and iodine combine to make a dark blue product and this will be the visual
test of your model.
Make a thick cornstarch mixture of 1 tsp (3 gm) cornstarch in 1/8 cup (20
ml) water. Put 3/4 cup (180 ml) hot water in a thick clear glass (like a
clear coffee mug or a 250 ml beaker). Slowly stir in the cornstarch slurry.
Have an adult partner put just under 3/4 cup (150 ml) water and 1 tsp (5 ml)
tincture of iodine in another clear glass. Cut off the top (ziploc side) of
a ziploc sandwich bag (not a freezer or storage bag). Pour about 1/4 cup of
the cornstarch solution into the bag (cleanly!). Close the bag tightly with
a twist tie. Gently set the bag in the iodine solution without letting the
twisted top get wet. Observe every 3 min for 15 min. Check for color
changes. Iodine molecules in the solution (orange) will flow by diffusion
through the pores in the bag to the inside, where there is no iodine yet
(flow is from concentrated to dilute). When iodine bumps into cornstarch
molecules, they react to make the dark blue complex. Which molecules were
able to travel through the pores of the bag, and which were not? What does
this tell you about the size of the molecules, the size of the pores, and
whether this is a good model of kidney dialysis?
Reference: David Thielk, ChemMatters, ACS, April 2001
To understand trick candles, you need to first understand how normal
candles work. The key difference lies in the moment after the candle is
blown out. In a normal candle, a smoldering ember in the wick causes a
ribbon of paraffin wax smoke to rise from the wick. While the ember is
plenty hot enough to vaporize paraffin, it is not hot enough to ignite the
paraffin vapors coming off.
The key to a trick candle, then, is to add something to the wick that
the ember is hot enough to ignite. After this material is ignited, the wick
becomes hot enough to light the paraffin vapors. The most common wick
additive is a metal called magnesium. Magnesium happens to burn (which
means to combine with oxygen to make light and heat) really quickly at a
fairly low temperature (low for fires anyway, at 800oF/430oC). Aluminum and iron metals both burn pretty well too, but they need higher temperatures.
Inside a burning wick, magnesium is shielded from oxygen and cooled by
melted paraffin. But once the flame goes out, the ember ignites magnesium
dust. If you watch the ember closely (and carefully!) youıll see tiny
flecks of magnesium flicking off. Just one of these is needed to provide
the heat that can re-light the paraffin vapors, and the candle flame comes
back to life. You wonıt see this happening to the wick of a normal birthday
candle. Check out these interesting weblinks for more information:
www.howstuffworks.com/question267.htm describes how regular candles work,
and www.delphion.com/details?pn=JP58049830A2 has the original 1983 Japanese
patent on trick candles.
Reference: Marshall Brainıs "How Stuff Works" website (with video) at
www.howstuffworks.com/question420.htm.
Proteins and Hard Boiled Eggs
Kids, did you ever wonder why eggs get hard when you boil them? It’s because they have lots of protein, especially in the egg whites. Here’s how it works. Protein is a polymer chain of amino acids that is flexible enough to fold up on itself in different ways based on their chemistry. It’s all wound up like a loose ball of string and held in place by weak bonds that are fairly easy to break apart. When that happens, the protein is called “denatured”. Have an adult help you to hard boil an egg. Imagine what’s going on inside the shell. When heated, the protein molecules gain enough energy to shake apart the weak bonds and the proteins begin to unfold. With time and more heat, new and stronger bonds are formed between different protein molecules. Another way to break the weak bonds is through chemical action. If you put a raw egg white in vinegar, the acetic acid will break some bonds in the egg. Use a dark bowl to help see it better. The egg white will start to set right away and get sort of pickled. When using an alcohol like vodka instead, the ethanol will break the weakest bonds in the protein. A lot of alcohol is needed, so really cover up the egg white. You should see some white strands form, but don’t be tempted to stir for this will just make a mess. You can see the greatest effect when both the alcohol and vinegar are used together. Notice the differences between these three different solutions and their effects on proteins. Mechanical energy will also work; whisking egg whites will unfold proteins and cause new bonds to form, and it stays in a new low-density “fluffier” state. A cooked, chemically-altered, or well-beaten egg white will never to go back to its original wet and gooey state. The yolk of the egg holds up better to both the mechanical energy and to the alcohol or vinegar attack. While there is a lot of protein in the yolk, there is also a lot of fat and other molecules that make it more difficult to denature. When hard-boiling eggs the recipe always calls for using a moderate heating process. High heat causes the proteins to get really tough and rubbery, and a chemical reaction between the yolk and the white leaves a green film around the yolk. Did you ever see this, maybe in an Easter egg? That film is actually iron sulfide, made from iron in the yolk and hydrogen sulfide from the white. It doesn’t hurt you of course and has no taste, but it doesn’t look too appetizing! Next check out these websites: www.hows tuffworks.com/question231 gives the scientific reason for the answer to the question of which came first, the chicken or the egg, and www.howstuffwork s.com/question85 describes how a chicken makes an egg using some really cool inorganic chemistry. --------------
Many of the elements are difficult to find in their pure state, but quite a
few are fairly easy to get a hold of. A list of suggestions along with
possible sources is provided below. How many of these elements can you
find? Can you find any others on the periodic table that we haven't thought
of here?
References: T. D. Burns, Chemistry Activity Book, 1995, Woodkrafter Kits,
Inc., Yarmouth, ME 04096-0808.
Fresco means "fresh" in Italian. Paintings done on wet plaster are called
frescoes because the plaster is fresh; this means that the plaster is still
wet when the artist paints on it. One of the most famous frescoes ever
painted took four years and was finished in 1512 by Michelangelo. It was
painted 70 feet above the ground on the ceiling of the Sistine Chapel in
Rome, Italy. Here we'll learn the technique that Michelangelo and his
helpers used to make this work of art.
The materials you will need are: a small disposable plastic dessert plate
and plastic cup, a "craft stick" (popsicle stick), plaster of Paris, water,
acrylic paints or poster paints, and a paintbrush. The procedure is to put
2 tablespoons (T) of plaster of Paris in a small cup, add 1 T of water, and
stir with the craft stick until the mixture is smooth. Pour the wet plaster
onto the plastic plate. Smooth the plaster out with the craft stick until
it covers the bottom of the plate. Dip the brush into one color of paint
and paint the plaster right away. Before the brush is dipped into the paint
a second time, rinse the paintbrush well in a cup of rinsewater. (If the
brush is not rinsed before being dipped into the paint each time, plaster
will get into the paint).
Is painting on plaster different than painting on paper? Experiment with
the interesting designs that can be made as the paint and paintbrush are
dragged through wet plaster. What happens to the surface of the plaster as
it begins to harden? Does it become more difficult to paint? When the
fresco is completely dry, twist the plate gently. This will loosen the
fresco so that it comes out easily.
So, what is the chemistry here? As the fresco dries, a chemical in the wet
plaster called calcium sulfate hydrate combines with water and hardens
before all the water can evaporate. Therefore it doesn't shrink, and the
fresco can last a very long time. If your fresco is kept safe it will last a
long time, too.
As an additional activity, consider entering the 2001 poster contest called
"Celebrating Chemistry: Then and Now". Judging categories are grades K-2, 3-5, 6-8, and 9-12. Call the ACS Office of Community Activities at
1-800-227-5558, ext. 6097 for details.
References: Go to the website www.acs.org/ncw for general details, and to the "activities and articles" section for this activity. We also used
www.artlex.com/ArtLex/p/plaster.html for this column.
Now for snowflakes. It all starts with a tiny particle of soil, ash, or dust in a cold cloud. Around this a hexagonal (six-sided) ice plate forms. A hexagon is the favorite shape of water molecules in an ice crystal lattice. The corners that stick out are better at catching other water molecules than the edges. Because the growing ice crystal is tumbling in the cloud, and sees different temperatures and saturation levels, an infinite variety of growing snowflake patterns are possible. Hence, no two snowflakes are alike!
Finally, here's a silly song, sung to the tune of "Rudolph the Red-Nosed Reindeer". (Yes, chemists know that pure iron is a silvery metal, but when it rusts you get a red iron oxide).
Iron the red-tinged atom
All of the other molecules
Then one inert Chemistry eve
Then how the atoms reacted
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Reference: Nancy Lang, Scientific American Explorations magazine, Fall
2000, p. 14 and www.redstaryeast.net/science.htm. See
www.breadworld.com/justkids for a peanut butter bread recipe with Fleischmannıs yeast.
Experiments with Yeast Part III of III
Kids, did you make your own bread from yeast according to the last few
columns? We hope you did, but if not you can still do quite a few
experiments with store bought yeast. The first experiment here tests how
sugar effects the growth of yeast. Fill two 1-cup glass measuring cups with
1/2 cup warm water. In one cup, add 1 tsp sugar. Put 1/4 ounce package of
active dry yeast in each cup, stir, and wait 10 minutes. Which cup has more
yeast foam and why? Is sugar necessary for the growth of yeast and why?
March, 2001
FIZZY FUN
Kids, baking soda and/or baking powder are added to cooking batters to
produce the gas bubbles that make cakes and muffins rise (this is called
"leavening"). It is caused by the action of baking soda plus a liquid acid.
Baking soda is sodium bicarbonate (NaHCO3). When mixed with a liquid acid
it releases the gas carbon dioxide (CO2). Of course you've seen this - when
you mix baking soda with vinegar it fizzes with CO2 bubbles. Recipes that
use baking soda for leavening always have an acid somewhere, like vinegar,
lemon juice, or buttermilk. Less obvious acids are those in honey and
molasses.
April, 2001
ChemLinks for Kids
Kids, in this column weıll put together some of our favorite internet
sites for chemistry experiments and learning activities at the
elementary school level. This is so that you have something to do in
between our monthly columns! One of our favorite resources through the
years has been the American Chemical Society magazine WonderScience. It
is now published solely on the web at www.acs.org/wondernet. Activities
investigate topics in science through fun, safe, and easy experiments
using inexpensive materials found in the home or grocery store.
May, 2001
A Medical Membrane Mimic
Kids, have you ever heard of kidney dialysis? Kidneys are essential for
keeping the proper chemical balance in our blood. They perform a wonderful
balancing act of filtration and osmosis that is not only essential to life,
but is extremely complicated. In very simple terms, the kidneys filter
blood in order to pass some dissolved salts, any toxins, urea, and
creatinine, along with a little water. When the body digests proteins, urea
is formed. But if too many urea molecules build up due to faulty kidneys,
they can cause serious diseases. So, doctors and chemists have worked
together over the years to perfect a process called hemodialysis. Chemists
have especially helped in creating the special artificial membranes now used
(hollow polysulfone fibers), which filter out urea but leave all the other
beneficial molecules behind (like red and white blood cells and essential
nutrients).
(www.acs.org/education/curriculum/chemmatt.html).
Patient Handbook, the Kidney Transplant/Dialysis Assn.
(www.ultranet.com/~ktda).
For extra info, check out www.kidney.org and www.niddk.nih.gov.
June, 2001
A Magnesium Marvel
Kids, have you ever wondered how those trick birthday candles work the
ones that keep re-lighting themselves after they are blown out? All you
need for this monthıs experiment is a regular birthday candle, a "trick"
birthday candle, matches, and an adult partner to light the candles for you.
August, 2001
Reference : Marshall Brain’s “How Stuff Works” website at www.howstuffworks.com /question616
October, 2001
Kids, did you ever think about building your own collection of chemical
elements? This can be a fun science project and a great "Show & Tell"
classroom session. Look back at our previous article on the periodic table
(June 1998) and also at http://pearl1.lanl.gov/periodic/ for great sites
that discuss the more than 100 pure elements that exist in the universe.
These sites will tell you the differences between elements, compounds (two or more elements bound together), and mixtures (two or more compounds).
There are others that are a bit hazardous and so you should only let an
adult partner handle them for you. Examples are mercury if kept contained
in a thermometer or thermostat switch, and tungsten filaments if left in
unbroken light bulbs.
November, 2001
Kids, a fun event called National Chemistry Week will take place this year
Nov. 4-10, 2001. Check other articles in the Bulletin and the Chicago Section web page for details in the
Chicago area. The theme this year is "Celebrating Chemistry & Art". One of the related activities suggested on the American Chemical Society's website will be highlighted here.
December, 2001
Kids, did you ever think of the Christmas tree as a chemical kind of plant? The wood of most any tree can be separated into two major components. They can be thought of as the "hard" and "soft" parts, which are the fiber (hard) parts and the oils and other soluble parts (soft). The hard or structural part of wood has very long molecules called polymers. They are cellulose (almost half of the wood is cellulose!) and lignin. Cellulose is the major ingredient in paper. The soluble parts of wood are extracted and separated using methods that chemists have developed. Think of the colors and flavors that are "extracted" from a steeping tea bag. Extracted oils from a spruce tree give turpentine, pine oil, and resins. There's only a tiny amount of pine oil (or alpha-terpineol), but it gives a pine tree it's distinctive Christmas smell.
References: www.santesson.com/christ/chemhome.htm for "Swedish Christmas Chemistry" and www.geocities.com/~ramarian/christmas/chemcarols.html for many "Chemistry Christmas Carols".
Iron the Red-Tinged Atom
There was Cobalt and Argone and Carbon and Fluorine
Silver and Boron and Neon and Bromine
But do you recall the most famous element of all?
Has a very shiny orbital
And if you ever saw him
You'd enjoy his magnetic glow
Used to laugh and call him Ferrum
They never let poor Iron
Join in any reaction games.
Santa came to say
Iron with your orbital so bright
Won't you catalyze the reaction tonight?
And combined in twos and threes
Iron the red-tinged atom
You'll go down in Chemistry!