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APRIL 2007
Paintball!Chemistry Hits Its Mark
Also: Coins, Coins, Coins!Also: Coins, Coins, Coins!
Paintball!Chemistry Hits Its Mark
2 ChemMatters, APRIL 2007
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Technical Review
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Teacher’s Guide
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Education Division
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By Bob Becker
QuestionFrom the Classroom
http://chemistry.org/education/chemmatters.html
Q: Lately, in chemistry class, we have been learning all about polymers. Our teacher shot some Silly String acrossthe room, and we read an article fromChemMatters about how SuperBalls aremade from polymers. So we know that poly-mers are fun, but what can they do thatreally matters?
A: A better question might be what
CAN’T they do? From clothing to medicine to
cars to computers ... you name it ... it’s proba-
bly made from—or made better by—poly-
mers. As you have learned, polymers are
long-chain molecules of repeating molecular
units, sometimes hundreds of thousands or
even millions of units long. That may seem
long, but longer still is the list of applications
for which polymers have been used in every
imaginable field.
One field that has gotten a lot of press
lately is the war in Iraq. Consider the following
examples that illustrate how polymers are
used for more than just fun and games.
Dyneema. This ultra strong, light-weight
polymer is reported to be 15 times stronger
than steel (and up to 40% stronger than
Kevlar, the polymer of which bullet-proof
vests have traditionally been made). Body
armor and flak jackets incorporate these poly-
mers, along with ceramic plates to help pro-
tect soldiers and civilians from bullets and the
shrapnel from explosive devices. Dyneema is
the trade name of extremely long chains of
polyethylene, also called high-performance
polyethylene (HPPE). The extreme length of
each individual molecule gives HPPE its
unique proper-
ties. Its density is
less than 1 so it
floats on water,
yet it is consid-
ered the
strongest fiber
in the world.
Kevlar. Panels made from Kevlar are
being used to help armor the fleet of
Humvees. Because its strength-to-weight ratio
is so much greater than steel, Kevlar can offer
the same protection as steel, without adding
all the extra weight, which would reduce the
speed and maneuverability of the vehicles.
Kevlar is also used to coat the floors of Black-
hawk helicopters.
Sodium polyacrylamide. Like sodium
polyacrylate, the super-absorbent polymer
used in disposable diapers, sodium polyacry-
lamide absorbs hundreds of times its weight in
water. So what does this have to do with troops
in Iraq? First, although helicopter pilots have
been well trained to fly in all sorts of weather
conditions, the desert climate is so dry that
huge amounts of sand and dust get stirred up
as they approach the ground. This can reduce
visibility to zero, and can lead to very treacher-
ous landings. Having a ground crew hose down
the landing area with water does not work all
that well. But
there is some-
thing about
sodium poly-
acrylamide that
binds to dust,
and sprinkling
a layer of the
polymer crys-
tals over the sand, raking it in, and then hosing
it down eliminates these rotorwash brownouts
completely. With an estimated three out of
every four helicopter accidents in Iraq and
Afghanistan attributed to these brownouts, a lit-
tle polymer can save a lot of lives.
What’s more, sodium polyacrylamide
has helped soldiers on the ground to stay
cool. Chunks of this polymer have been sewn
into cotton bandanas. During the scorching
summer months, these are then soaked in
water and draped around the soldiers’ necks.
As the water evaporates off the bandana, this
endothermic process helps to cool down the
bandana, as well as the person wearing it. The
polymer inside then releases some of its
absorbed water and the evaporation can con-
tinue for many more hours of cooling than a
simple water-soaked bandana could provide.
A third use for this superabsorbent poly-
mer is in self-pressurizing tourniquets.
Tourniquets are nothing new; for centuries,
straps have been tightened around soldiers’
limbs to prevent blood loss. You see them in
just about every war movie ever made. But the
C
H
C
H
H
H
n
C
H
H
C
C
H
O
NH2
n
Dyneema, where n > 100,000
polyacrylamide
JUPITER IM
AGES
®
Vol. 25, No. 2 APRIL 2007
ChemMatters, APRIL 2007 3
use of tourniquets is actually quite controver-
sial: the restriction of blood flow often results
in the loss of what otherwise would have been
a healthy arm or leg. How do you apply
enough pressure to minimize blood loss, but
not restrict blood flow to the rest of the limb?
Hemodyne (a company in Virginia) has come
up with a solution: the BioHemostat is a ban-
dage which absorbs the blood—thanks to the
sodium polyacrylamide inside—and as it
expands, it applies just the right pressure to
stop the bleeding but not the blood flow.
Semiconducting organic polymers, or
SOPs. A research team at MIT led by chemist
Tim Swager and electrical engineer Vladimir
Bulovic has designed a new line of SOPs that
have the capacity to sniff out explosives with
greater sensitivity than any other detection
method yet developed. When ultraviolet light
of just the right intensity is shined upon a film
of these SOPs, the film produces laser light.
But when a molecule of trinitrotoluene (TNT)
binds onto the polymer chain, the laser action
ceases. This effect is sensitive enough to
detect TNT molecules at concentrations of
only a few parts per billion. According to the
researchers, new technologies for explosives
sensing could help protect soldiers from
improvised explosive devices (IEDs), one of
the greatest threats facing Coalition Forces in
Iraq. Enhancing the sensitivity of these detec-
tion systems could increase the distance at
which explosives can be identified, giving the
soldiers greater standoff capabilities.
Silly String. (That’s right: Silly String!)
Whereas SOPs may pave the way for a very
high-tech IED-detection system, a much
lower-tech solution comes in a can—and in a
variety of bright, festive colors.
This is ingenuity at its best.
Before searching a build-
ing, ground troops have
taken up the practice of
spraying Silly String
across the doorways
and into each
room. The IEDs
are often trig-
gered by extremely fine,
nearly invisible trip wires. When the
strands of Silly String land on the floor, the
room is considered safe to enter. But when
the strands get caught in mid air ... soldiers
beware! Better living through chemistry, no
doubt. If only all of the challenges in Iraq had
such simple solutions.
Question From the Classroom 2How are polymers used in the war in Iraq?
Paintball! Chemistry Hits Its Mark 4You may be surprised to find out how much chemistry isinvolved in this super-popular sport. Keep your head down!
Gold in Your Tank 8From the offshore platform to the refinery, to the gas pump,see how gasoline makes its way from deep, deep under-ground to your car.
Retiring Old Tires 11Somewhere around 300 million used tires are generatedeach year in the United States. Sometimes gigantic pilesof them catch fire with devastating results. What can bedone with old tires? The world can only use so manytire swings!
The Captivating Chemistry of Coins 14Did you ever wonder how a soda machine knows whensomeone tries to slip it a Canadian dime? There’s a lotof chemistry behind coins.
The Death of Alexander Litvinenko 18As this issue goes to press, the assassination of Alexander Litvinenko remains unsolved. The poisoning case involves police and intelligence officials from three
different countries as well as Interpol, the international police force.
Chem.matters.links 20
CMTEACHERS! FIND YOUR COMPLETE
TEACHER’S GUIDE FOR THIS ISSUE ATwww.chemistry.org/education/chemmatters.html.
GETTY IMAGES
MIKE CIESIELSKI
MIGUEL CRUZ
ASSOCIATED PRESS IMAGES
PaintballsPaintballs are a marvel of both engineering and chemistry. They must be
strong enough to be fired at an initial velocity of up to 91 m/s (200 mph) without
breaking, yet burst open when they hit someone without causing any tissue dam-
age beyond mild bruising. The deformation of the paintball on contact greatly
increases its stopping time, thus lessening the force (and the sting) of its
impact. To accomplish this task, paintballs are made with a tough but elastic
outer coating of gelatin, with a liquid center. The process by which liquids are
manufactured within a gelatin shell is known as encapsulation.
Encapsulation technology originated with the pharmaceutical industry.
The process involves enclosing a substance—either liquid or solid—within a
thin transparent gelatin membrane. These capsules are commonly called soft
gels, since they are somewhat elastic and give a little when squeezed. Soft gels
are commonly used for medicine, vitamins, bath oil beads, and a variety of
other applications.
Gelatin is made from denatured collagen
fibers, which are derived from the skin, bones,
and connective tissue of animals. The gelatin for
paintballs is usually made from pig skins, which
tend to make the best paintball. A plasticizer is
also added to increase stability and make the
gelatin more moldable. The gelatin-
plasticizer ratio is formulated so as to
establish the optimal balance between
elasticity and brittleness, enabling the
paintball to break open on impact yet
not break when initially fired.
http://chemistry.org/education/chemmatters.html4 ChemMatters, APRIL 2007
our heart is pounding
as your adrenalin skyrockets.
Projectiles whiz past your head as you
dive for cover behind a makeshift ply-
wood barrier. You return fire, but you know
you are outnumbered. The enemy is closing in.
Suddenly, you’re hit. You reach for the wound.
Your fingers are covered in a sticky red liquid. You
have become another casualty. Fortunately, the red liquid
is not blood, and the battle you have bravely fought is not
actual combat—it is the exhilarating sport of paintball!
The first paintballs were fired by foresters and ranchers
to mark trees and cattle. Then someone got the bright idea that
it would be more fun to fire paintballs at people than at trees
and cows. Thus the sport of paintball was born. From its incep-
tion in the 1980s, the sport has grown by leaps and bounds.
Today, over 10 million people participate annually in paintball
games. Over 1 billion paintballs are produced each year!
Although there are numerous variations, players typi-
cally attempt to capture an opponent’s flag without being shot
by a paintball. The first team to capture the opponent’s flag
and return it safely to their territory is the winner. The
action is fast and furious, with a typical game lasting
anywhere from 5 to 30 minutes. Sound dangerous?
Other than a little bruising, it’s actually safer than
golf because of the protective face gear that all
players are required to wear. And the game
itself would not be possible without—you
guessed it—chemistry!
By Brian RohrigY PHOTOS BY MIGUEL CRUZ
Chemistry Hits Its Mark
MIKE CIESIELSKI
Though technically not water soluble, gelatin does break down in
water to form a colloidal gel. That is why it is so important to keep
paintballs dry. Gelatin is used in a variety of foods. Jell-O, marshmal-
lows, gummy bears, ice cream, yogurt, cream cheese, and margarine all
contain gelatin. Its unique constitution helps to give foods thickness and
texture. And it provides the perfect medium to keep the paintball
intact—until it hits you!
A typical paintball is 68 caliber, meaning its diameter is 0.68 inches
(1.7 cm). They are also available in other sizes as well. Paintballs come
in a variety of colors; some glow in the dark, others fluoresce under
black light.
The first paintballs were not water soluble, since they were similar
to the original formulation which was used to mark trees and cattle.
When a forester marks a tree, it is important that rain not wash off the
mark. The first paintball contests resulted in a lot of stained and ruined
clothing, to the chagrin of many parents.
In the mid-1980s, the paintball manufacturers decided to make a
water-soluble paintball. This was a daunting task, since the “paint” for
the paintballs could not contain any water or else they would break
down the gelatin shell. This feat was accomplished by using water-sol-
uble compounds, but not water itself. And once paintballs became water
soluble, the popularity of the sport skyrocketed.
After much research, it was determined that polyethylene glycol
(PEG) would be an excellent substance for the liquid inside of a paintball.
Polyethylene glycol is a tasteless, colorless, and nearly odorless
compound that dissolves in water but has no effect on the gelatin shell.
PEG is very viscous, meaning it
flows slowly. Its thick syrupy con-
sistency makes it perfect for use
in paintballs; they have a consis-
tency somewhat like blood when
they break open.
That’s swellIf a paintball is dropped into a beaker of water, it will expand to an
impressive size. Through osmosis, water will pass through the gelatin
membrane and hydrogen bond with the polyethylene glycol within.
Since the concentration of water is much greater outside of the paintball
than inside, water will diffuse inward in an attempt to equalize the con-
centration of water. Water will continue to travel through the gelatin
membrane until the concen-
tration of water inside the
paintball is equal to the con-
centration of the water on
the outside of the paintball.
However, as it swells the
gelatin shell will break down,
spilling the contents before
equilibrium is reached.
As you can see, paintballs
are not really made from paint,
but rather from a mixture of non-
toxic food grade ingredients. The exact
combination of ingredients is a trade
secret but we do know that in addition to
polyethylene glycol, they also contain col-
ored food dyes, preservatives, and a thickener such as
starch or wax. The ingredients within the paintball are
also biodegradable, so they pose no threat to wildlife or
the environment.
Bonding with your paintballsWhat makes paintballs water soluble? The answer lies in polarity
and hydrogen bonding. Water is a polar substance that has distinct
regions of positive and negative charge. Water’s polarity is due to the
differences in electronegativity between oxygen and hydrogen. Elec-
tronegativity, as defined by the late American chemist Linus Pauling, is
“the power of an atom in a molecule to attract electrons to itself.” Oxy-
ChemMatters, APRIL 2007 5
Outsidethe paintball
Membrane
Low WATER
concentration
High WATER
concentration
Direction of movement
Insidethe paintball
Lewis diagram Space-filling diagram
Two representations of water, showing regions of partial charges.H
O
OH
n
H Hδ
δ
δO
+ +
-
• • • •
δ+ δ+
δ-
polyethylene glycol, PEG Are all molecules with polar bonds polar?
The answer is no; in some cases, the polarity of the bonds is effec-
tively cancelled. Consider a CO2 molecule. Oxygen is more elec-
tronegative than carbon, so the covalent bond between the two
atoms is polar. This is called a polar covalent bond; the O-H bond in
a water molecule is also polar covalent. The polar nature of this bond
is indicated by the arrow ( ) in the figure below. But the linear
nature of the CO2 molecule dictates that, overall, the molecule is non-
polar. That’s because while one oxygen atom is drawing bonding
electrons toward itself, the oxygen atom on the other side of the mol-
ecule is doing the same thing; the net effect is that they cancel each
other out. That makes CO2 a nonpolar molecule.
So when predicting the polarity of a molecule, the shape must
be considered. Often, molecules that are symmetrical will be nonpo-
lar even if polar bonds are present.
Lewis Diagram Space-filling diagram
Two representations of CO2, showing an overall nonpolar molecule.
O OC
• •
• •
• •
• •
Osmosis: a paintball swells up when placedin water.
CESAR CAMINERO
gen is more electronegative than
hydrogen, so it attracts elec-
trons to itself more strongly
than does hydrogen. For a
water molecule, this creates
a region of partial negative
charge (�-) on the side of
the oxygen atom, and a
region of partial positive
charge (�+) on the side of
the hydrogen atoms.
Because of the shape of the
water molecule, these polar
bonds make the molecule polar
overall.
Polar molecules are attracted to
other polar molecules. This attraction is
due to the positive side of a polar molecule
being attracted to the negative side of another polar molecule. This
attraction is the basis of the intermolecular bonding that may occur
when one substance dissolves into another. This tendency is summed
up nicely in the principle “like dissolves like,” meaning that polar sub-
stances dissolve in other polar substances.
We can take a closer look at the interaction between water and
polyethylene glycol molecules. The oxygen atoms in the polyethylene
glycol chain each have two nonbonding electron pairs. The partial posi-
tive charges around the hydrogen atoms in water are attracted by these
nonbonding electrons. This particular type of intermolecular attraction is
called a hydrogen bond. Hydrogen bonds occur when a hydrogen atom
attached to a small, highly electronegative atom (typically F, N, or O) is
in the vicinity of an atom with nonbonding electron pairs. Although not
as strong as covalent or ionic bonds, hydrogen bonds are the strongest
of the intermolecular forces. The hydrogen bonds between water mole-
cules are responsible for its unusually high boiling point.
The dyes used in paintballs are also polar and water soluble. The
polar nature of the polyethylene glycol enables these water-soluble dyes
to be dissolved within the paintball. We can’t show you the structures of
the dyes because they are proprietary—that means a closely guarded
secret. But the colored dyes and the polyethylene glycol are water solu-
ble, so today, when a paintball combatant returns from the field of battle
and her clothes are splattered with paint, they simply need to be thrown
into the wash and they will generally come out clean—though it may
take more than one washing!
Magic markersThe firing instruments used to shoot the paintballs
have come a long way since the game began.
Known as markers rather than
guns, they have evolved
from hand-cocked,
single-shot pistols
into rapid-firing,
high-precision instru-
ments. The “marker”
term arose from the
first use of paintballs,
which was to mark trees
and cattle. The term also
gives the sport of paintball a
less violent image.
The markers come in a
variety of makes and models—
from pistols to semiautomatic rifles.
Some models can fire 100 paintballs
at 30 per second using a single 12-
gram CO2 cartridge. Extra large hoppers (the storage chamber that holds
the paintballs before they are fired) can hold up to 250 paintballs. Fully
automatic models are available, but these are prohibited on most playing
fields. There are even paintball “landmines” that will spray paint all over
whoever is unfortunate enough to step on one.
Markers all operate on the same basic principle—using compressed
gas to launch a paintball. Gases can be readily compressed because there
is so much space between the molecules. When the marker is cocked, a
paintball falls from the hopper into the barrel. When the trigger is pulled, a
quick blast of compressed gas is released directly behind the paintball,
propelling it forward at an initial velocity up to 91 m/s.
It’s a gasThe most common gas used in paintball markers is compressed
CO2. The CO2 within a gas canister is at an
extremely high pressure—around
800–850 psi (pounds per square inch). At
this pressure, however, CO2 will actually
liquefy. So, within the high-pressure con-
fines of a gas cartridge, much of the CO2will typically exist as a liquid. The liquid is
actually responsible for controlling the
pressure of the CO2. As long as there is
6 ChemMatters, APRIL 2007 http://chemistry.org/education/chemmatters.html
Volu
me
Pressure
Boyle’s Law
H H HH
HH
OO
O
• •
• •
• •
• •
• •
• •
Hydrogen bonding between water molecules.
Hydrogen bonding (blue lines) between polyethylene glycol and water.Hydrogen bonds are about 1/15th the strength of a covalent bond. Red = oxygen atoms, grey = carbon atoms, and white = hydrogen atoms.
JUPITER IMAGES
MIGUEL CRUZ
ChemMatters, APRIL 2007 7
some liquid present, the pressure of the gas in contact with the liquid
will remain constant. The pressure of the gas will equal the vapor pres-
sure of the liquid. Thus, the pressure of the CO2 will stay constant for
each shot; if there were no liquid present, releasing the gas would
decrease the pressure of the remaining gas. However, if the
marker is fired many times in succession, the pressure will tem-
porarily drop since it takes some time for the liquid CO2 to vapor-
ize and restore the pressure.
The vapor pressure of CO2 at room temperature
is about 60 times atmospheric pressure. To prevent a
canister from exploding under high pressure,
CO2 tanks are fitted with a copper burst disk
that is made to pop off if
the pressure exceeds a safe
level. This varies
between 2200 psi
and 2800 psi, depending on
the manufacturer.
When a small
amount of this gas is
released, it expands
greatly, since it is now
under much less pres-
sure. Boyle’s law states that the
volume of a gas is inversely pro-
portional to its pressure, so long as
the temperature is held constant. Inversely
proportional means that when one factor
decreases, the other increases. When the volume of a
gas goes down, its pressure goes up. Likewise, when the
pressure decreases, the volume increases.
The paintball is propelled forward by the increase in the volume of
the CO2, which is due to the decrease in pressure the gas experiences
as it leaves the cartridge and enters the firing chamber. The only thing
standing in the way of the expanding gas is the paintball, which is
launched effortlessly through the air.
Just do it.The sport of paintball is highly addictive. Serious players can
spend hundreds, or even thousands, of dollars on
high-tech gear. There are numerous organized
leagues and tournaments in nearly every
state and in countries around the
world.
Even the U.S. Army is
getting into the game; they
have made an arrangement
to sponsor the Long Island
Big Game, to be held
May 19–20, 2007,
in New York. Orga-
nizers expect over
2000 players, and the
game will feature tanks, a heli-
copter, missions, and prizes.
A few bruises are a small
price to pay for a sport that not
only is immensely entertaining, but
also teaches strategy, builds team-
work, and provides great
exercise. And if that upcoming
chemistry test is stressing you
out, there is no better way to
relieve that stress than by
heading to the woods with
some friends and blasting each
other with spheres of brightly
colored gelatin-encapsulated
solutions of pigment-infused poly-
ethylene glycol!
Ten tips from tourney players
Get in shape: It’s a physical sport.Eat well, stay active, and cut badhabits such as smoking.
Protect yourself: Cover up with appropriate gear to prevent bruises or a
blood clot.
Know the rules and abide by the do’s and don’ts.Be a good sport.
Learn to shoot with either hand. This increasesyour mobility.
Be unpredictable:Make yourself a harder target forthe competition.
Prepare: Study the game and walk the field. Packyour gear the night before.
Communicate with team members. Tournamentplayers yell at each other constantly.
Practice: Simple drills can improve your aim.
Be safe: Always wear your mask, listen to the ref,and follow the rules of the field.
Always treat a marker as if it is loaded.
Can you find the density of a paintball?
Paintballs come in various sizes, but a typical paintball will have a
diameter of 1.7 cm and a mass of 3.1 grams. Can you determine the
density of a paintball? The formula for the volume of a sphere is 4/3 � r3.
The formula for density is m/v.
You can find the answer on page 20.
REFERENCES
Chemical Institute of Canada.
http://ncwsnc.cheminst.ca/articles/1994_paintballs_e.html (accessedFeb 2007). Paintballs and Canadian National Chemistry Week.
Enotes.com. http://science.enotes.com/how-products-encyclopedia/paintball (accessed Feb 2007). How paintballs aremade.
Madpaintballer.com.http://www.madpaintballer.com/make_paintballs.php (accessed Feb2007). How to make paintballs and more.
Brian Rohrig teaches at Jonathan Alder High School in Plain City, OH. His mostrecent ChemMatters article, “NASCAR: Chemistry on the Fast Track,” appearedin the February 2007 issue.
MIGUELCRUZ
8 ChemMatters, APRIL 2007
young lady pulls into a station
and up to a pump. Through the
nozzle and into the car’s tank
flows a slightly yellowish liquid
about the consistency of nail polish remover.
She pays about $2.50 a gallon and continues
on her way. Most of you know that the gaso-
line that she pumped came from crude oil. But
the motor oil that reduces friction in the
engine, part of the tires on her car, the plastic
parts inside the car, the plastic of her sun-
glasses, the fabric of her jacket, and the medi-
cine in the bottle in her purse were also
manufactured from crude oil—the thick, black
substance also known as petroleum.
Texas teaFor years, oil has been known as “black
gold,” among other terms. The hydrocarbons
(molecules made of carbon and hydrogen)
found in petroleum are among the most
important chemicals known. They are the
reactants used for manufacturing plastics,
medicines, fertilizers, pesticides, insecticides,
and a multitude of other products. Many of
these compounds possess an enormous
amount of chemical energy; the combustion
of a gallon of gas can release 1.32 � 108
Joules of energy. If a gallon of gasoline could
be used as food, it would be the equivalent of
31,000 food calories. That’s enough
to feed a teenager for about two weeks!
Crude oil is about 84% carbon,
14% hydrogen, and 2% other ele-
ments, such as sulfur and nitrogen.
The chemicals in gasoline after it has
been refined from crude oil are mostly hydro-
carbon chains of varying length. The carbon
and hydrogen atoms came from once-living
organisms.
Decomposed Remains + Pressure + Heat = Oil
Plants and animals died in ancient seas
10 to 600 million years ago and their remains
sank into the mud. In the layers of mud, little
or no oxygen was present as microorganisms
decomposed the remains. As more layers of
sediment piled up, the pressure and heat
increased, converting the decayed remains into
a mixture of hydrocarbons—our crude oil.
What do the hydrocarbons in crude oil
look like? Most of the molecules are satu-
rated, meaning that they only contain single
bonds. Saturated hydrocarbons are known as
alkanes. Here are some simple alkanes:
Natural gas used for heating and cooking
is about 75% methane, an odorless gas. The
“rotten egg” odor that you smell when you
leave the gas stove on is from either hydrogen
sulfide (H2S) or dimethyl sulfide (CH3SCH3),
added for the purpose of detecting leaks or to
alert you that a burner is left on. Propane and
butane are common fuels that you may
already be familiar with.
The first four compounds of the alkane
family are shown in Table 1; the series contin-
ues with pentane (C5H12), hexane (C6H14),
heptane (C7H16), octane (C8H18), nonane
(C9H20), and decane (C10H22). Can you come
up with a general molecular formula that fits
all alkanes? (Check the end of this story for
the answer.)
Finding and
extracting the oilGeologists have a variety of methods for
finding oil. They use satellite images to exam-
ine surface terrain or cameras to reveal ocean
floor features. Instruments are used to detect
minute changes in the earth’s gravitational or
magnetic fields caused by flowing oil. Some-
times, geologists create shock waves with
explosions or thumper trucks that pound into
the ground. The passage of the shock wave
through rock layers is measured by seismo-
logical instruments. Different types of rock
transmit the shock wave at different speeds,
allowing geologists to map out the structure
and reveal oil pockets.
Once the oil is discovered, a drilling rig is
brought in. Test wells are drilled to determine
whether the deposit is worth developing. If the
oil is under an ocean, an offshore rig is
erected over the spot. A crew occupies the
offshore platforms for up to three weeks at a
time and then rotates with another crew.
Sleeping quarters, cafeterias, and recreational
areas are placed around the platform along
with the drilling equipment. Transport to the
platform can be by boat or by helicopter. The
work continues day and night.
Oil platforms are huge structures that
rise above the ocean surface. In fairly shallow
http://chemistry.org/education/chemmatters.html
GoldTankin Your
A
By Roberta Baxter
GETTY IMAGES
ChemMatters, APRIL 2007 9
waters, and up to 1700 feet, fixed platforms
have legs anchored to the ocean floor. In
deeper waters, oil companies use floating
platforms attached to the floor by cables.
One of the largest structures in the world
is above the Petronius oil field, about 130
miles southeast of New Orleans. The field was
discovered in 1995 and is estimated to have
100 million barrels of oil at a depth of 1734
feet under the ocean surface. The oil platform
over the field is anchored to the ocean floor
and rises 2000 feet above the surface, nearly
four times taller than the Washington Monu-
ment. Total weight of the platform is about
43,000 tons.
After the crude oil is pumped from the
well to the surface, it is transported to a refin-
ery by an oil tanker or through a pipeline.
Refining oilCrude oil contains thousands of chemi-
cals that must be separated. The first step in
the refining process involves the use of a frac-
tional distillation column. The hydrocarbons
found in oil have different boiling points, the
property that is exploited in order to separate
them. First, the crude oil is heated until it
vaporizes. The vapor travels up a fractional
distillation column filled with trays or plates.
As the vapor rises through the column, the
temperature drops. When a compound
reaches the area of the column that is at a
temperature equal to its boiling point, it con-
denses on a tray, flows out of the column, and
is collected as a liquid or gas. The vaporized
compounds with the lowest boiling points
travel to the top of the column, the coolest
section, before they condense. Each conden-
sate is known as a fraction.
Materials such as asphalt, fuel oil, and
engine oil have high boiling points, so they are
extracted near the bottom of the distillation col-
umn. Other chemicals, such as diesel fuel,
kerosene, and gasoline come off in the middle.
Small molecules such as methane and ethane
are collected at the very top of the column.
A hydrocarbon’s boiling point is depen-
dent on the forces of attraction between the
molecules or the intermolecular attractions.
For the nonpolar hydrocarbons, only Van der
Waals (also called London dispersion; see
ChemMatters, December, 2006, p. 9) forces
are at work. Fritz London, a German-American
physicist, suggested that these forces result
from fleeting, instantaneous charge imbal-
ances or dipoles in a molecule. The temporary
dipole in one molecule induces a dipole in
neighboring molecules, which, in turn, induce
still more dipoles in other molecules. The com-
bination of temporary and induced dipoles cre-
ates an attractive force between the molecules.
The possibilities for these interactions to occur
go up with increasing molecular size and sur-
face. The general rule is that as the size of mol-
ecule increases, so do the London forces.
Small hydrocarbons with little surface
area (less than 5 carbons) tend to be gases
because very little intermolecular attractions
exist. Medium-sized molecules (C5 to C9)
have greater London forces and tend to be
liquids at room temperature. Large hydrocar-
bons (C10 and up) with greater surface area
and more electrons have substantial inter-
molecular attractions and thus tend to be oils
and waxes.
Improving the
fractionsGasoline is not a single compound; it is a
complex mixture of hydrocarbons, including
isomers of octane and other additives. Com-
pounds suitable for gasoline only make up
about 40% of the crude oil. The world’s
energy dependence requires more than that,
so chemical processes are added to the refin-
ing process. Three ways to make more useful
compounds out of those coming off the frac-
tionation column include:
• Cracking—breaking large hydrocarbonsdown
• Unification—combining smaller hydrocarbons
• Alteration—rearranging molecules
Cracking is accomplished by either ther-
mal decomposition or catalytic reaction. In
thermal cracking, heavy gas oil (molecules
with >20 carbon atoms) is heated with steam
to 1,500 ˚F (816 ˚C). The long carbon chains
break into smaller chains, which include
octane and those that can be used for other
products. In catalytic cracking, catalysts are
added to the mixture so that the process can
take place at lower temperature and pressure.
The catalysts used are compounds of alu-
minum and silicon, such as aluminum
hydrosilicate, bauxite, and silica-alumina.
Catalysts are also required for unification
reactions; platinum and platinum-rhenium
mixtures are often used. These reactions com-
Name Molecular Structural formula Condensed Usesformula structural formula
methane CH4 CH4 Natural gas
ethane C2H6 CH3CH3 Fuel
propane C3H8 CH3CH2CH3 Camping
stove fuel
butane C4H10 CH3CH2CH2CH3 Heating fuel,
disposablelighters
C
H
H H
H
C
H
H C
H
H
H
H
C
H
H C
H
H
H
C
H
H
H
C
H
H C
H
H
H
C
H
H
C
H
H
H
Concrete platform
500 m
Floating platform
WashingtonMonument (169 m) Offshore oil drilling platforms
Table 1. Simple alkanes
CESAR CAMINERO
bine smaller hydrocarbon molecules into
longer chains. The reactions also produce
hydrogen gas, which is collected and sold.
The alteration process involves catalysts
and hydrofluoric or sulfuric acids. The mole-
cules of double-bonded hydrocarbons, such
as propylene and butylene, are converted into
octane isomers by alkylation. A simplified
illustration of the process is shown. In this
case, isobutylene (A) is treated with a catalyst
and a strong acid (H+). This causes the double
bond to become protonated, that is, one of the
carbon atoms of the double bond now has a
new hydrogen atom attached. This leaves the
other carbon atom from the double bond with
a deficiency of electrons and thus a positive
charge. This hydrocarbon with a positive
charge is called a carbocation (B). Carboca-
tions are very reactive so they don’t hang
around for long; they are referred to as “reac-
tive intermediates” because they exist only for
a fleeting moment before they react with
something else. In this case, the carbocation
reacts with another molecule of isobutylene,
forming yet another carbocation (C). At this
point, the reaction can take many different
paths. In this example, isobutane is added and
iso-octane, the prized component of gaso-
line, is formed. Notice that this step also
forms intermediate (B), which continues the
process. Being able to control the outcome of
these reactions is of
supreme importance
to refinery chemical
engineers. New cata-
lysts are being devel-
oped all of the time.
Once the desired
compound is made, it
is purified to remove unreacted reagents.
Then it is run through an absorption column
to remove water and through sulfur scrubbers
to remove sulfur compounds. Now it’s time to
blend the compounds to make gasoline with
different octane levels.
What is an octane
rating?The octane ratings shown on gas pumps
indicate how much a fuel can be compressed
before it ignites spontaneously. In a gas
engine, the piston compresses the gas-air
mixture. Once it is compressed, the mixture is
ignited by the spark plug. If the gas ignites
prematurely and without the spark from the
spark plug, it causes knocking and possible
engine damage. Octane ratings and gasoline
additives were presented in a recent Chem-
Matters article (Volume 25, No. 1, February,
2007), so it won’t be repeated here. But in a
nutshell, the octane rating gives you an idea of
how the gas will perform with respect to
knocking. For example, an octane rating of 87
tells you that the gas has the same resistance
to preignition as a mixture of 87% iso-octane
and 13% heptane.
Oil fields from around the world supply
the gasoline to fuel our cars, the reactants to
make numerous products, and the oil to heat
our homes. Geologists will search for new
fields to meet the demand, and scientists will
continue to devise better ways to drill for,
transport, and refine oil. Until we find the
means to treat our addiction to it, oil will
remain valuable enough to claim the nickname
“black gold.”
SOURCES
Graham, I. Fossil Fuels; Raintree Steck-Vaughn: Austin, TX, 1999.
Speight, J. Petroleum Chemistry andRefining; Taylor & Francis: Washington,D.C., 1998.
Snedden, R. Energy From Fossil Fuels;Heinemann: Portsmouth, NH, 2006.
Chevron Corporation.http://www.chevron.com/products/learning_center (accessed Jan 2007).
U.S. Environmental Protection Agency.http://www.epa.gov (accessed Jan 2007).
http://www.howstuffworks.com. (accessedJan 2007). Articles on how gasolineworks, how oil refineries work, how to drillfor oil.
Roberta Baxter is a science writer who lives inColorado Springs, CO. Her most recentChemMatters article, “Chemistry Builds a GreenHome,” appeared in the October 2006 issue.
http://chemistry.org/education/chemmatters.html10 ChemMatters, APRIL 2007
C C
HCH3
H
C C
H
H
H
C C
H
C
C
CH
H
C
C
CH
H
H
H3C
CH3
CH3
catalysts
catalysts
H3C CH
3
iso-octane
+
+H3C
H
H3C
H3C
H3C
H3CH+
H3C
CH3
A B
C
(D)
CH3H
3C
C H
H3C
H3C
H3C
CH3
Iso-octane may be formed from smaller molecules via alkylation reactions.
Liquifiedpetroleum gas
Chemicals
Petrol forvehicles
Jet fuel,paraffin forlighting andheating
Diesel fuels
Crude oil
Fractionatingcolumn
Fractionsincreasing indensity andboiling point
Fractionsdecreasing indensity andboiling point
Lubricatingoils, waxes,polishes
Fuel for ships,factories, andcentral heating
Bitumen forroads androofing
C5 to Cgnaphtha
C5 to C10 petrol(gasoline)
C10 to C16 kerosine(paraffin oil)
C14 to C20diesel oils
C20 to C70fuel oil
>C70 residue
20oC
70oC
120oC
170oC
270oC
600oC
C1 to C4 gases
C20 to C50lubricating oil
350oC
Answer to question: The general formula forany alkane is CnH2n+2.
Schematic of a refinery fractional distillation column.
CESAR CAMINERO
ChemMatters, APRIL 2007 11
resently, approximately 300 million used tires are generated annually in the
United States alone. In the early 1990s the growing stockpiles of scrap tires
reached as many as 3 billion, with at least another 240 million adding to the
problem every year. Although limited uses were found for about one-quarter
of them, the others remained, layer upon layer, in surface storage sites and
landfills. There, they collected stagnant water and housed disease-spreading insects
and rodents. Worst of all, they frequently caught on fire.
Burning ring of tireActually, why not burn them? Just ask anyone who has been anywhere near a
burning heap of tires; they will tell you that you don’t want to go there. Thick solid tires,
unlike granular coal or liquid petroleum, burn slowly, releasing black clouds of noxious
volatile organic compounds (VOCs). For every kilogram of tire, approximately 11 g of
VOCs, 4 g of semi-volatiles, and 4 g of polycyclic aromatic hydrocarbons (PAHs)—
especially dangerous carcinogens—are released into the atmosphere. Given the fact
that the average tire weighs about 9 kg, you can appreciate the environmental impact
of a burning heap of tires.
In February 1990, an arsonist
ignited 14 million scrap tires piled out-
side the town of Hagersville, Ontario,
Canada. The fire burned for an agonizing
17 days, caused the evacuation of over
4000 people, and cost over $10 million in
firefighting and clean-up costs. A similar
fire plagued Wesley, CA, in September
1999, when firefighters from several
states joined local firefighters to extin-
guish the blaze that started in a storage
site containing 5 million tires.GETTY IMAGES
You’re walking through a city
neighborhood and suddenly—
what’s this?—you’re bouncing
and springing along the side-
walk. You look down, and the
pavement is some vibrant
shade of brown or red—no
graffiti, cracks, or chalked
messages. Nice! Pedestrians
with tired feet are giving it
rave reviews. Tree roots can
bend it but not crack it. What
is it? It’s one of the new rub-
berized surfacing materials
generated from old tires. And
the good news is that we’re
not going to run out of that
source any time soon.
P
PbZn
Some of the materials released when tires burn:
benzene 1,3-butadiene benzo[a]pyrene
volatile organic compounds a polycyclic aromatic compound metals
Retiring ld Tires
By Donald Jones and Helen Herlocker
CA INTEGRATED WASTE MANAGEMENT BOARD-TODD THALHAMER
Firefighters and environmental workers
dread tire fires! They are especially difficult to
extinguish when compared to other fires.
Extreme heat liquefies the rubber, turning it
into oil. With each tire generating about two
gallons of oil as it burns and liquefies, a fire
like the one in Ontario can release over 20 mil-
lion gallons of toxic oil to either burn or leach
into the soil of surrounding farmlands.
RubberNatural rubber, a wet sticky plant prod-
uct, is an example of a polymer, a molecule in
which repeating molecular subunits form
chains. These chains are generally linked to
one another by atomic bridges called cross-
links. It’s the number of these cross-links that
give rubber its characteristic properties.
History credits New Jersey chemist
Charles Goodyear for inventing a process in
the mid-19th cen-
tury for controlling
the number of
cross-links in
uncured rubber. The
initial result was a
product much more
durable and chemi-
cally resistant than
the original, but
would begin to deteriorate within a few days,
gradually breaking down into a wet crumbly
mess. Vulcanization, a chemical process
named after Vulcan, the Roman god of fire,
adds more cross-links by introducing sulfur at
high temperatures. Along the rubber molecule,
there are several sites called cure sites, which
are particularly attractive to sulfur atoms. Dur-
ing vulcanization, highly reactive sulfur atoms
form chain-like bridges that span from a cure
site on one rubber molecule to one on a neigh-
boring molecule.
Chemists have developed ways to control
the vulcanization process to favor either short
or long sulfur cross-links between rubber
molecules. Short cross-links (1 or 2 sulfur
atoms) result in a product with good heat
resistance, while longer cross-links (3–8 sul-
fur atoms) give the rubber more elasticity and
flexibility. Blends of natural and synthetic rub-
ber (along with many other materials) can be
used to make a very sturdy automobile tire
that can last around 40,000 miles.
Then what?Given the danger, public safety issues,
and the negative environmental impact of
costly tire fires, all but eight states have laws
severely restricting the disposal of scrap tires
in landfills. In some rural areas, regulations
like these have led to unfortunate measures of
local convenience. Streams, rivers, and hill-
sides are often found littered with old tires with
no uses and no immediate means of disposal.
So, what do you do with hundreds of
millions of old tires? Just as the problem
seemed hopeless and the stockpiles were
reaching a critical mass, economic reality
entered the picture. The cost of virgin rubber
on the world market started to rise as dramati-
cally as the price of crude oil rose. Manufac-
turers began eyeing the vast and growing
stockpiles of rubber tires with new interest.
Today, new and creative uses for recycled
tires, like the sidewalk mentioned earlier, are
springing to the forefront.
Three uses for an
old tire
Light my tire
The first use—as fuel—may be particu-
larly hard to believe, given all we’ve said
about burning tires! But
nearly half of the used tires
generated in the United
States over the past few
years have become tire-
derived fuel (TDF), provid-
ing energy for a variety of
industrial and public utility
applications. Major users
include cement kilns, pulp
and paper mills, electric
utilities, and various indus-
trial boilers. In all three
uses the steel “bead” used
to attach the tire to the rim
of the wheel is removed before shredding.
For some applications, whole tires, including
their fabric and steel components, are used.
In others, whole tires are preshredded to
expose more surface area for combustion.
Burned under carefully controlled conditions,
the energy recovered per ton of tires is
somewhat larger than that for coal and about
the same as for oil—not so surprising given
the largely hydrocarbon composition of vul-
canized rubber.
TDF has another advantage: Under the
right conditions, it is a cleaner fuel than either
coal or oil. With no nitrogen content, TDF
combustion results in less nitrogen oxide
(NOx) emissions into the atmosphere.
Although any burning in the presence of air
will result in a reaction between atmospheric
nitrogen and oxygen to form NOx, fuels like
certain coals and oils bring enough of their
own nitrogen to the mix to increase NOx emis-
sions dramatically. Oil can contribute as much
as 50% of the total, and coal, as much as
80%. As for TDF, make that a zero. Burning
TDF will result, however, in some SO2 emis-
sions, because of the sulfur introduced in the
vulcanization process.
Engineering projects
A second broad area of use for about
20% of used tires is in civil engineering pro-
jects—projects taking advantage of the chem-
ical stability and resilience of vulcanized
rubber. For these projects, tires are shredded
into tire-derived aggregates (TDA)—pieces
and particles ranging in size from 2 to 12
inches depending on the intended use. The
U.S. Scrap Tire Markets 2003 Edition, pub-
lished by the Rubber Manufacturers Associa-
tion, describes several applications for TDAs.
12 ChemMatters, APRIL 2007 http://chemistry.org/education/chemmatters.html
H3C
S
x
catalyst
H3C
xS
z
H3C x
z = 1-2
Shoulder
Steel Belts
Tread AreaGrovesRib
Bead Chaffers
Bead
Radial Plies
Cap Plies
cross-linked polyisoprene
polyisoprene
Parts of a tire.
COURTESY OF THE GOODYEAR TIRE & RUBBER COMPANY
Spiral WoundCap Plies
COURTESY OF THE GOODYEAR TIRE & RUBBER COMPANY
Vulcanization of natural rubber
Charles Goodyear
Most of them are used as filler in landfills,
where their superior properties make them
useful for enhancing drainage, venting gases,
closing caps, lining collection vessels, and
providing additional surface cover. In addition,
less costly than stone, TDAs work well in sep-
tic drain fields, where they enhance the
drainage spaces for wastes. For large-scale,
civil engineering projects, TDAs are valued as
subgrade fill for embankments, where the
existing soils are too weak for the task. You
might see TDAs at work in highway construc-
tion projects as fill material behind walls and
bridge abutments—
projects in which the
light weight, superior
drainage properties,
and low-cost make
TDAs the best choice
for the job.
Crumb rubberproducts
The third applica-
tion for scrap tires,
about 11% of them,
includes a growing
array of products
requiring an initial and
somewhat costly pretreatment to yield crumb
rubber. For these applications, the steel and
fabric components of the tire must be sepa-
rated away, leaving the vulcanized rubber to
be ground or cut to the required crumb size.
Imagine the logistics. It would be difficult
enough to rip away the fabric and steel from
one tire. But for hundreds of millions of them?
The task on that scale requires knowledge of
the physical and chemical properties of all of
the tire components. One separation strategy
begins by physically grinding whole tires into
pieces of about 2 inches in diameter. These
pieces are fed into a granulator where their
size is reduced even further. At this stage, the
remaining steel is removed by magnets, and
the fibers are sifted out on shaking screens.
Finally, the separated rubber is refined to the
particle size
required by the
manufacturer.
A second
method, called the
cryogenic method,
uses liquid nitro-
gen or super-
cooled air to freeze
the ground tire
stock into solid
chips. A hammer
mill pounds and
shatters the chips,
liberating the steel
and fabric in the
process. Then, as in the previous method,
magnets and sifters remove the extraneous
material, leaving exceptionally clean vulcan-
ized rubber. By either method, clean crumb
rubber is generated for any use to which
costly virgin rubber is suited.
The applications and
demands for crumb rubber
increase every year. About
one-third of it is used in the
manufacture of rubber-modi-
fied asphalt (RMA), for a wide
variety of surfaces. Arizona
and California use most of the
available RMA with growing
demands in Florida, Texas,
and other states. While initial
production costs are high,
RMA produces long-lasting
road surfaces with low main-
tenance requirements, thereby
making it cost effective in the
long run. Used on highways,
RMA surfaces reduce noise
and shorten braking dis-
tances—features appreciated
by consumers. Resilient and
stable crumb rubber is attrac-
tive for surfaces under playground equipment,
as a soil additive under athletic fields, and as
surface material for tracks—applications with
obvious human safety advantages.
Clean crumb rubber has one more obvi-
ous use, one that may eventually overtake all
of the others—tire manufacturing! Presently,
it constitutes a portion—about 10% in the
United States—of the mix used to manufac-
ture new tires.
Looking to the futureHow far have we come toward solving
the environmental problem of scrap tires?
Recall that in the early 1990s there was a
growing mountain of them, as many as 3 bil-
lion crowding landfills and other collection
sites. Then, only about 25% of scrap tires
were being reused and repurposed. Today, the
news is getting better—a lot better thanks to
economic realities and new industrial tech-
niques. Today, about 80% of our annual crop
of 300 million used tires will find new uses.
And as for that stockpile? There are about a
quarter of a billion left. Got any ideas?
REFERENCES:
U.S. Scrap Tire Markets—2003 Edition,Rubber Manufacturers Association, 1400K Street, NW, Washington, DC 20005(July 2004).
EPA web site;http://www.epa.gov/epaoswer/non-hw/muncpl/tires/basic.htm. Managementof scrap tires.
Kurt Reschner, http://www.entire-engineer-ing.de/str/Scrap_Tire_Recycling.pdf.Scrap tire recycling.
Donald Jones, an active ACS member, taughtchemistry at MacDaniel College in Maryland. HelenHerlocker, a science writer, is a former editor ofChemMatters.
ChemMatters, APRIL 2007 13
The Goodyear P195/75R14,
a popular sized tire, weighs about
21 pounds and contains:
Approximate Composition
Carbon 85%
Ferric material 10–15%
Sulfur 0.9 to1.25%
How about getting 40,000 miles out of a pair of sandals? Forinformation on how you can make your own pair of tire sandals,go to http://www.hollowtop.com/sandals.htm.
PHOTOS COURTESY OF THOMAS J. ELPEL, WWW.GREENUNIVERSITY.NET.
What’s in your tires?
Crumb rubber may be used for shock absorbingplayground floors.
Making sandals from old tires!Making sandals from old tires!
PHOTOS COURTESY OF TOTTURF.COM
ave you ever stood in
front of a vending
machine, pumping in
your change, and the
machine just kept
spitting out one dime,
until you realized that it was a
Canadian dime? Why can’t you use Canadian
coins in American vending machines, and vice
versa? And how do vending machines distin-
guish between real money and fake money?
What are our coins made of? Are nickels
made of nickel? These questions and many
more will be answered as we examine the
captivating chemistry of coins!
Early cashMetallic money has been around for thou-
sands of years, while paper money has only
been popular for a few hundred years. The
first coins were worth their face value of what-
ever precious metal they were made from.
Today, all coins are deliberately made to be
worth
less than their face
value, so as to
prevent them from being melted down and the
metals recovered and sold. All coins were
originally made from gold, silver, and copper,
and these elements are still referred to as the
coinage metals. The drachma and denarius,
which were widespread in Greek and Roman
times, were composed of silver. The aureus, a
gold coin, was also popular.
AlloysAlthough some ancient coins were
sometimes made from pure metals, today, all
coins intended for circulation are made from
alloys. An alloy is a homogeneous mixture of
two or more elements, one of which must be
a metal. There are numerous advan-
tages to using alloys. Alloys typically are
harder, more durable, and more corrosion
resistant than the pure metals by themselves.
Pure gold and silver, for example, are very
soft, and would not hold up to the wear and
tear that circulated coins experience. Even the
ancients were well aware of the advantages of
alloys, as bronze was a common material
used to make coins. The development of
bronze was so
important that an
entire historical
era—the Bronze
Age—was named
in its honor. The
bronze alloy
used to make
coins today is
typically com-
posed of 95%
copper, 4% tin,
and 1% zinc.
14 ChemMatters, APRIL 2007 http://chemistry.org/education/chemmatters.html
h
By Brian Rohrig
MIKE CIESIELSKI
MIKE CIESIELSK
I
A newer coin, the Sacagawea dollar,
looks like a gold coin. It is actually made from
an inner core of copper surrounded by an
outer layer of manganese brass (an alloy of
copper, zinc, manganese, and nickel). Brass
was chosen because of its gold color, since
previous dollar coins were disliked by con-
sumers because they too closely resembled
other silver coins such as quarters. Brass is
an extremely durable metal with excellent cor-
rosion resistance, as evidenced by its com-
mon use in instruments and plumbing
fixtures.
Even though the 1792 Mint Act man-
dated that all American coins be made from
copper, silver, or gold, few American coins
today actually contain these metals. They have
become far too expensive. These precious
metals have been replaced with cheaper met-
als, even though most coins do tend to retain
the appearance of the more valuable metals.
A pretty pennyThe ubiquitous penny used to be made
mostly of copper but is now mostly zinc. Zinc
is much less expensive than copper. Today’s
penny is made up of 97.5% zinc, with a paper-
thin copper coating that only makes up 2.5%
of its total mass. This change came about in
1982. From 1962 to 1982, the penny was
95% copper and 5% zinc. This makeover
came about because the value of the copper in
a penny began to approach one cent and
looked like it might rise higher. As a result,
there were nationwide penny shortages due to
incessant hoarding.
There are several ways to distinguish
between old and new pennies. A post-1982
penny has a mass of 2.5 grams, while the pre-
1982 pennies have a mass of 3.1 grams. 1982pennies may have either mass. Since all pen-
nies have an identical volume, a greater mass
indicates a greater density. Copper is denser
than zinc. (The density of Cu is 8.96 g/cm3,
while that of Zn is 7.13 g/cm3.)
Another big difference between old and
new pennies is their melting point. If heated
over a Bunsen burner, the new penny will be
reduced to a silvery liquid blob in just a few
moments. The older copper pennies can be
heated over a Bunsen burner flame without
melting. Zinc melts at a much lower tempera-
ture than copper. The melting point of zinc is
420˚C, while that of copper is 1083˚C.
Don’t eat the changeBefore 1982, if a small child swallowed a
penny, doctors would generally advise to just
let it pass, since the hydrochloric acid (HCl) in
the gastric juices of the stomach will not react
with copper. If you are familiar with the metal
activity series, then you will know that zinc is
more reactive than copper, and HCl will react
with zinc.
If a newer penny is swallowed and the
copper coating has worn thin or has devel-
oped even a tiny crack, the HCl in the stomach
can react with the zinc within the penny. If the
penny remains in the stomach long enough, it
can develop some jagged edges as the stom-
ach acid eats away at it. These jagged edges
can potentially perforate the intestine as the
penny passes through the digestive system.
However, most of the time these swallowed
pennies pass with little harm done.
Changing
changeThe penny is not the only coin to
undergo a makeover in recent years. The
Coinage Act, passed by Congress in 1965,
mandated that silver be either removed or
eliminated from dimes, quarters, and half dol-
lars. Silver was completely removed from
dimes and quarters in 1965 and replaced with
an outer layer of a copper-nickel alloy bonded
to an inner core of pure copper. In 1971, the
composition of all half dollar and “silver” dol-
lar coins were changed to that of the dime and
the quarter. With coins nowadays, little is as it
appears. Not only are our “copper” pennies
mostly zinc, but our “silver” coins are mostly
copper!
Dimes and quarters minted before 1965
were composed of an alloy of 90% silver and
10% copper, and they are considered some-
what valuable by collectors. You can easily
test for the presence of silver with a simple
experiment. Rub a little mustard on a silver
coin and also on a nonsilver coin and let them
stand overnight. In the morning, rub off the
ChemMatters, APRIL 2007 15
Thin copper outer layer
Zinc core
Cross-section showing the structure andcomposition of a post-1982 penny.
2 HCl(aq) + Zn(s) � H2(g) + ZnCl2(aq)
Mustard mystery? If you suspect you have a“silver” coin, apply a generous portion ofmustard to it and let it sit overnight.
MIKE CIESIELSKI
In the morning, remove the mustard. If silver isindeed present, there will be a tell-tale blackspot, indicating Ag2S.
The mass of a penny tells you whether it wasmade before or after 1982.
MIKE CIESIELSKI
MIKE CIESIELSKI
mustard. A black spot will remain on the silver
coin, but not on the nonsilver coin. Mustard
naturally contains sulfur compounds, and sul-
fur reacts with silver to form a black precipi-
tate of silver sulfide (Ag2S).
Coin magnetismEver wonder why Canadian coins cannot
be used in American vending machines, and
vice versa? To answer this question, test a
number of American coins with a magnet. It is
doubtful you will find any that are
attracted. The only exception is
the 1943 zinc-plated steel
penny, which was manu-
factured during World
War II to conserve
copper for the war
effort. There are
only three ele-
ments that are
ferromagnetic
(strongly
attracted to a
magnet) at room
temperature.
These are iron,
nickel, and cobalt.
Even the nickel coin con-
tains only 25% nickel. The
rest is copper. The concentration of
nickel is not great
enough to make the coin
ferromagnetic.
When you place a
coin in a vending
machine, up to a dozen
tests may be performed
to verify whether a coin
is genuine. Sensors
within the vending
machine measure the
coin’s weight, diameter,
and rolling
speed. An electrical current
passes through each
coin deposited to
determine its rate of
conductivity, thus
determining its
metallic content.
The coin also
passes through
the poles of a
magnet. If a
coin is magnetic,
it is rejected by
the machine.
In Canada, the
vending machines must
be arrayed differently, since
most Canadian coins are mag-
netic. However, Canadian nickels have been
made mostly from copper since 1982. But
Canadian dimes, quarters, and one and two
dollar coins are still mostly made from nickel
and therefore are strongly attracted to a
magnet.
One bus driver in Alberta, Canada, used
the magnetic properties of Canadian coins to
his advantage. Every day after work for 13
years, he would collect a number of coins
from the coin collection unit on his bus using
Experiments With Pennies:1. See how many drops of water you can place on a penny, using an eyedropper.
Because of the incredible surface tension of water, you can fit an
astonishing number of drops on a penny before they will tumble off.
2. Determine which household substance is the best copper cleaner.
Immerse discolored pennies in various household solutions, such
as pop, juice, milk, vinegar, ketchup, lemon juice, and detergent.
Leave the pennies immersed for 1 week. Remove the pennies and
examine them. Which substance did the best job at cleaning the
pennies? Which did the worst job?
3. Place several shiny pennies between the layers of a paper towel
that has been soaked in vinegar. Sprinkle some salt on the pennies
as well. The next day, observe what happens. The pennies will have
developed a green coating of verdigris, or copper (II) acetate. See
Feb. 2003 issue of ChemMatters for more details.
http://chemistry.org/education/chemmatters.html16 ChemMatters, APRIL 2007
1.
2.
3.
MIKE CIESIELSKI
MIKE CIESIELSKI
MIKE CIESIELSKI
a long pole with a magnet attached to the end.
He collected a fortune, amassing over $2.3
million. But he was eventually arrested, arous-
ing suspicions when he purchased an
$800,000 house on an annual salary of only
$38,000!
An interesting experiment can be con-
ducted with a pre-1982 Canadian nickel, a
magnet, and a Bunsen burner. Place the
nickel on the magnet, and holding the mag-
net with tongs, heat the nickel over the Bun-
sen burner flame. After a short while, the
nickel will fall off! When heated, ferromag-
netic substances lose their magnetic proper-
ties. Substances are magnetic because tiny
regions within the material known as
domains are all aligned in the same direction.
When heated, these domains become
unaligned, causing the substance to lose its
magnetic attraction. After the nickel cools,
the domains realign and it will once again be
attracted to a magnet. The temperature at
which a substance loses its magnetic proper-
ties is known as its Curie point. For nickel,
the Curie point is 375 ˚C, easily obtainable
with a Bunsen burner.
If you have some foreign coins at home,
test them with a magnet. Some will be mag-
netic, but most will not. British pennies are
magnetic, as they are made of copper-plated
steel. They are even part of a popular chil-
dren’s toy where a magnetic pyramid is
constructed.
Loonie tooniesThe two-dollar Canadian coin—
affectionately known as the
toonie—is a fascinating amal-
gam of art and chemistry. It is
composed of an outer ring of
mostly nickel, with a gold-
colored inner disk of 92%
copper, 6% aluminum, and
2% nickel. The outer ring
is strongly attracted to a
magnet, but the inner ring
is not. If this coin is heated
strongly over a Bunsen
burner flame and then quickly
submerged in cold water, the
smaller inner coin can be made to
pop out!
All metals expand when heated, but not
at the same rate. The amount of expansion a
material experiences when heated is known as
its coefficient of linear expansion. Copper has
a higher rate of expansion when heated than
nickel, which also means that copper shrinks
more rapidly when cooled. When plunged into
cool water directly after heating, the inner coin
will shrink at a greater rate than the outer ring,
causing the inner coin to fall out.
When the toonie was first introduced in
1996, some defective coins would separate if
given a hard blow or frozen. For many Cana-
dians, it was great sport to see if the two
parts of the toonie could be separated. Wear-
ing the smaller inner coin as a necklace was
even considered a fashion statement. This
flaw in the toonie was corrected not long after
its debut. It is currently against the law in
Canada to deliberately separate the two parts
of a toonie.
Well, hopefully some of the questions at
the beginning of the story have now been
answered. Whether jingling in your pocket or
slung around your neck on a chain, coins
provide you with yet another opportunity to
discover chemistry in everyday items.
The
one-dollar
Canadian coin is known
as a “loonie,” for the
picture of the loon on its face.
The “toonie” is the slang for the
two-dollar Canadian coin (which
alludes to both “two” by
analogy with the
loonie, and to
“Looney Tunes,”
again paired with
the loonie).
ChemMatters, APRIL 2007 17
Brian Rohrig teaches at Jonathan Alder HighSchool in Plain City, OH. His most recentChemMatters article, “NASCAR: Chemistry on theFast Track,” appeared in the February 2007 issue.
REFERENCES
Hagenbaugh, B. A penny saved couldbecome a penny spurned. USA Today.July 7, 2006, pp. 1B–2B.
Huss, F. Ferromagnetism and the CuriePoint. Chem 13 News. Dec, 1989, p. 6.
McClure, M. Chemical Counterfeit Catcher.ChemMatters, Oct. 1997, pp. 13-15.
Yeoman, R.S. The Official Red Book: AGuide Book of United States Coins, 60thEdition. Whitman Publishing: Atlanta, GA,2006.
Wikipedia. http://en.wikipedia.org/wiki/Toonie
Science Learning Center. http://www.fi.edu/pieces/knox/mustardtrick.htm
18 ChemMatters, APRIL 2007
November 1, 2006. Three or possi-
bly four men meet in the bar of
London’s Millennium Hotel. One
is Alexander Litvinenko, a fiercely
outspoken critic of the Russian government
and an ex-KGB agent. The others are Russian
businessmen Dmitri Kovtun, Andrei Lugovoi,
and possibly Vyacheslav Sokolenko, all of
whom have either current or past ties to the
Russian intelligence community. A second
meeting with an Italian security consultant at a
Piccadilly sushi bar, Itsu, took place later that
evening. Other meetings take place in and
around London that day. The number of meet-
ings and their locations are shrouded in mys-
tery; the substance of their discussions,
unknown. What is known is that hours later,
Litvinenko became seriously ill, allegedly the
result of an intentional poisoning. Twenty-two
days later, Litvinenko died of a previously
unheard of method of execution; poisoning
with a rare radioactive isotope—polonium-210.
An ex-spyAlexander Valterovich Litvinenko was
born in 1962 in the Russian city of Voronezh.
At one time, Litvinenko transferred from the
military into the FSB (the Russian Federal
Security Service, which succeeded the KGB,
an organization similar to the CIA), rising to
the rank of lieutenant-colonel. His area of spe-
cialty was fighting organized crime, which no
doubt made him some enemies. His disen-
chantment with the FSB and his falling out
with Vladimir Putin (the current president of
Russia), stems from the 1990s when Putin
was the head of the FSB. Since that time,
Litvinenko became an outspoken writer and a
vehement critic of the Russian government,
and Mr. Putin, in particular. In 1998, Litvi-
nenko participated in a televised news confer-
ence in Moscow with other FSB officers. They
claimed that their superiors had ordered them
to assassinate people.
In the days following the November 1
meetings, Litvinenko’s hair fell out, his throat
became swollen, his bone marrow was
attacked, and his immune and nervous sys-
tems became fatally damaged. After a valiant
effort by doctors at London’s University Col-
lege Hospital, Litvinenko died of heart failure
22 agonizing days after his exposure to polo-
nium-210 (210Po).
Early on, British security sources
revealed that MI5, the British counter-intelli-
gence and security agency, had identified the
FSB as the most likely culprit. From his
deathbed, Litvinenko stated his belief that his
death was ordered by Russian president
Vladimir Putin himself.
Polonium-210Polonium-210 is a rare, naturally occur-
ring radioactive element found in minute
amounts in the earth’s crust. It was once used
as a trigger in nuclear weapons. In this capac-
ity, 210Po is alloyed with beryllium (Be). The210Po fires off an alpha particle, which is
absorbed by the Be, which subsequently spits
out a neutron, initiating the uncontrolled chain
reaction characteristic of nuclear fission. The210Po decays into stable 206Pb after releasing
the α-particle. Alpha decay causes the ele-
ment to lose four mass units, and the atomic
number is reduced by two.
AlexanderLitvinenko
The Death of
He4
2
Po210
84
Pb206
82
By Audrey Keown
Po Pb He
Be C n
210
84
206
82
4
2+
10
4+ He
4
2
13
6+
1
0
A. Litvinenko in 2002 holding a copy of his book,in which he alleged that agents from the FSBcoordinated the 1999 apartment block bombingsin Russia that killed more than 300 people.
ASSOCIATED PRESS IMAGES
Polonium-210 decays by alpha emission.
Using a 210Po/10Be alloy to trigger a nuclearweapon.
CESAR CAMINERO
ChemMatters, APRIL 2007 19
Discovered by Marie Sklodowska-Curie
and her husband Pierre Curie in 1898, it was
tentatively called Radium F. Polonium was
later renamed in honor of Marie’s native land
of Poland (Latin: Polonia).
There are 25 known isotopes of polo-
nium, and all of them have short half-lives. A
half-life is the time it takes for 1/2 of a radioac-
tive sample to decay to half of its initial value.
The products of nuclear decay are called
daughter nuclei. The range of atomic masses
of these isotopes is 194 – 218 amu, with210Po being the most abundant.
Polonium-210 is made by bombarding
bismuth-209 with neutrons (that came from U-
235) in nuclear reactors. The Bi-209 absorbs a
neutron to become Bi-210, which sponta-
neously decays into Po-210 by beta emission.
Beta particles are high-energy electrons. In the
process of beta emission, a neutron in the
nucleus is converted into a proton and an elec-
tron. The electron is ejected from the nucleus
as the energetic beta particle. Thus, beta decay
causes the element to gain one proton, but the
mass number remains the same.
210Po can be made from 209Bi. The beta particle(β) has a charge of 1-.
Biological hazardsThe half-life of 210Po is only 138 days. It
decays by alpha emission, that is, it emits
alpha particles, which are essentially high-
energy helium nuclei. The alpha particles are
high energy, but they have little penetrating
ability—a single sheet of paper will stop them
dead in their tracks. The particles are fired out
of the polonium nucleus with 5.3 MeV of
energy, which is more than 1 million times
more energy needed to rupture a chemical
bond. Because of their low penetrating ability,
the particles are not harmful as long as the
polonium is located outside the body. But if210Po is ingested, it becomes extremely dan-
gerous. If only 1 �g of 210Po is ingested, that
corresponds roughly to 3 quadrillion (3� 1015)
atoms of the radioactive isotope. This is
enough for potentially hundreds of 210Po iso-
topes to interact with each and every cell in a
person’s body. As the polonium atoms fire out
the high-energy alpha particles, extreme dam-
age occurs via ionization and radical forma-
tion. Proteins are destroyed and DNA is
cleaved, making a mess of the internal func-
tioning of the body.
It is theorized that alpha particles
destroyed the fragile stem cells in Litvi-
nenko’s bone marrow. Stem cells are
required for the maintenance of red blood
cells and the immune system. A detailed
autopsy was not possible at the time of this
writing; the body was considered too danger-
ous to be safely handled.
Where did the 210Pocome from?It has already been mentioned that 210Po
is very rare. Furthermore, the production and
distribution of 210Po is tightly controlled.
There are no producers in Britain or the United
States. Nearly all of the known 210Po produc-
tion worldwide takes place in Russian nuclear
reactors, and almost all of it (less than 1 gram
per year) is imported to the United States. In
the United States the 210Po is safely embed-
ded in ceramic, so it may be used in static
elimination equipment.
The United States keeps tabs on the
imported 210Po. Although it can be used to
trigger a nuclear bomb, the likelihood of a ter-
rorist group attaining a significant amount of
fissionable fuel such as U-235 is small. They
could, however, use the 210Po along with con-
ventional explosives to make a “dirty bomb”
that would spread radioactive particles, creat-
ing a radioactive contamination hazard.
The investigation
continues …If pure 210Po was smuggled into Britain,
authorities there have reason for concern.
How did it get across the border, and how
was it diverted? Interpol, the international
police organization, has been called in to help
coordinate the investigation, which now spans
across three countries—Britain, Russia, and
Germany. It will be some time before all of the
evidence is in concerning Litvinenko’s death.
The evidence concerning his alleged poison-
ing will no doubt take even longer to con-
clude. Stay tuned to ChemMatters; we will be
watching as the story continues to develop.
When all of the facts are uncovered, expect to
see a future issue with the conclusion to this
extraordinary story.
REFERENCES
Amato, I. How Polonium Poisons. Chemicaland Engineering News, Dec 4, 2006, p 15.
Lide, D., ed. CRC Handbook of Chemistryand Physics, 76th ed. CRC Press: NewYork, 1995.
Eubanks, L., Middlecamp, C., Pienta, N.,Heltzel, C., Weaver, G. Chemistry inContext, 5th ed. McGraw-Hill HigherEducation: Dubuque, IA, 2005, Chapter 7.
United States Nuclear RegulatoryCommission. http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/true-or-false.html (accessed Jan 2007)
BBC News. http://news.bbc.co.uk/1/hi/health/6181688.stm (accessed Jan 2007)
USA Today. http://www.usatoday.com/news/world/2006-12-13-polonium-guide_x.htm.(accessed Jan 2007)
Audrey Keown is a freelance writer based inKansas, who lives with her dog Jaspur.
ASSOCIATED PRESS IMAGES
Bi n Bi209
83
1
0
210
83+ Po
210
84�+
Investigators arrive in front of a Hamburg hometo check for traces of polonium. The case nowinvolves police and intelligence officials fromthree different countries, as well as Interpol, theinternational police force.
German police seal the door of a Hamburgapartment building after finding traces ofradiation in an apartment apparently used byDmitri Kovtun.
ASSOCIATED PRESS IMAGES
Comparing the penetrating ability of differenttypes of radiation. Alpha particles can be stoppedby a sheet of paper or skin. Beta radiation can bestopped by glass, plastic, metal, or wood. Densematerials such as lead, steel, or concrete arerequired to shield against gamma radiation.
CESAR CAMINERO
ChemMatters wins
award!
We are pleased to announce that
ChemMatters has won the 2006 Distin-
guished Technical Communication
Award from the Society for Technical
Communication. The magazine has
also advanced to the STC’s Interna-
tional Technical Publications Competi-
tion, the results of which will be
announced in the spring of 2007.
Plastic that is stronger
than steel
One way to express the strength of a
fiber is its free breaking length, the
theoretical length of a fiber that breaks
under its own weight when freely
hanging. Independent of the thickness
of the fiber, the free breaking length
depends only on the composition of
the material. The free breaking length
of the high-performance polyethylene
polymer Dyneema must be infinite.
According to DSM, the maker of
Dyneema, a rope made of the material
could, in theory, reach to a satellite in
orbit. Imagine an elevator to a space
station some day! For more informa-
tion about the incredible properties of
this polymer, take a look at
http://www.dsm.com/en_US/htm
l/hpf/home_dyneema.htm.
Paintball!
You have read all about what’s in a
paintball, but if you would like to learn
more about how one is assembled,
this Web site is for you: http://
www.rps-paintball.com/
process.asp.
And for everything else you wanted
to know about paintballs but were
afraid to ask, head to http://www.
pcri.net/specialedition4.htm. For a
paintball dictionary, go to
http://www.paintballnexus.com/
dictionary.php.
And when you absolutely positively
need to know where your paintball is
going to land, try this paintball trajec-
tory calculator: http://home.
comcast.net/~dyrgcmn/
pball/trajectory.html.
Paintball density (m/V) answer: To
find the volume, use 4/3 � r3. The
radius is found by taking 1/2 the diame-
ter. 1.7 cm � 2 = 0.85 cm, so V = 4/3
� (0.85)3 = 2.6 cm3 = 2.6 mL. Then
d = 3.1 g/2.6 mL = 1.19 g/mL. This
means the paintball will sink in water,
since water has a density of ~1 g/mL.
Are there any fluids that can keep a
paintball afloat?
More on oil
For amazing virtual tours of offshore
drilling platforms, check out
http://resources.schoolscience.
co.uk/SPE/index.html and
http://resources.schoolscience.
co.uk/exxonmobil/index.html.
ChemMatters at your
fingertips
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Also, the new 1983–2006 ChemMat-
ters Index is available for only $12. Call
1-800-227-5558, or order online at
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Chemists Celebrate
Earth Day
The Chemists Celebrate Earth Day
(CCED) theme is “Recycling—Chem-
istry Can!” Celebrate anytime of the
week of April 22, 2007.
Enter the K–12 grade
illustrated haiku con-
test to win a local
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contest. Start a
recycling program
at your school or increase awareness
about the benefits of recycling.
More information about CCED, the
contest, American Chemical Society
local contacts, and local events is
available at http://chemistry.org/
earthday.
Teachers, look here!
The Discovery Channel Young Scientist
Challenge (DCYSC) is a national sci-
ence contest for middle school stu-
dents in the 5th through 8th grades.
The contest identifies and honors
“America’s Top
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1155 Sixteenth Street, NWWashington, DC 20036-4800
Reach Us on the Web at
chemistry.org/education/chemmatters.html
A publication of the Education Division of the American Chemical Society
Chem.matters.links
Ship armored with Dyneema.
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