®

APRIL 2007

Paintball!Chemistry Hits Its Mark

Also: Coins, Coins, Coins!Also: Coins, Coins, Coins!

Paintball!Chemistry Hits Its Mark

2 ChemMatters, APRIL 2007

Production Team

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Administrative Team

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Peter Isikoff, Administrative Associate

Technical Review

Seth Brown, University of Notre Dame

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Teacher’s Guide

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Donald McKinney, Editor

Mark Michalovic, Editor

Ronald Tempest, Editor

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Education Division

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Programs

Policy Board

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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

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tion about the incredible properties of

this polymer, take a look at

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l/hpf/home_dyneema.htm.

Paintball!

You have read all about what’s in a

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process.asp.

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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.

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Chemists Celebrate

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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

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