Light Sticks Liquid Light
Just give the plastic light stick a little "snap" and a shake and the liquid inside begins
to glow. Some people call it liquid light. Our experience tells us that with light comes
heat... but not this time. Light sticks are more popular than ever and have become
almost required apparel for Halloween to cast an eerie glow on the candy seekers.
Light sticks are also a great and inexpensive teaching tool for students to learn how
temperature affects the rate of the chemical reaction.
Caution! This experiment requires the use of very warm water... which requires the
assistance of an adult helper.
Materials
Take advantage of the holiday and stock up on some light sticks during the
Halloween close-outs. You'll need three light sticks of the same size and color for this
experiment. You'll also need two glass containers (coffee cups or beakers work well)
and a darkened room.
Experiment
In the following experiment, you'll observe the differences in the brightness of the light
given off from a light stick placed in hot water and and an identical light stick placed in
cold water.
1.In a darkened room, remove one light stick from its package and feel the outside of
the light stick to determine its approximate temperature. Bend the light stick until you
hear it “snap” and the liquid begins to glow. Shake the light stick to mix the liquid
inside. Feel the outside of the light stick again. Has the temperature changed?
2.Ask an adult to fill one of the glass containers with cold water (a mixture of water
and ice) and the other with hot water. Ideally you would like to have the hot water
around 50 degrees C / 120 degrees F. Be careful not to make the water too hot
(above 70 degrees C / 158 degrees F) because it can melt the plastic of the light
stick. Never place a light stick in water that is being heated.
3.At the same time place one light stick in the hot water and place one light stick in
the ice water. Leave the third light stick at room temperature. How long does it takes
for a change to occur in the hot-water light stick and in the ice-water light stick? What
happens to the light intensity or brightness of each light stick? Look closely at the hot-
water light stick without removing it from its container. Notice the bubbles rising to the
top of the light stick. Compare the rate of bubble formation between the three light
sticks. If you have difficulty seeing the bubbles forming, you may have to remove the
light sticks from their containers and hold them up to a light source such as a
window. What causes the bubbles to form?
4.After a few minutes, reverse the light sticks so that the warm light stick will be
placed into the cold water, and the cold light stick into the warm water. How long does
it takes for the intensity to change (how long will it take the dim light stick to brighten,
and the bright one to dim)?
5.Remove the light sticks from the hot water and the ice water. Allow them to come to
room temperature. What happens? How long do you observe any changes?
How does it work?
When light is produced from a chemical reaction, such as this one, the resulting light
is called “chemiluminescence” (say, “chemy-lew-min-ess-cents). The light is said to
be “cool” because no heat is produced during the reaction. The reaction between the
different chemicals in a light stick causes a substantial release of energy. When the
chemicals are mixed, the atoms are excited, causing electrons to rise to a higher
energy level and then return to their normal levels. When the electrons return to their
normal levels, they release energy as light. This process is called
chemiluminesence. The chemical reaction in a light stick usually involves several
different steps. A typical commercial light stick holds a hydrogen peroxide solution
and a solution containing a phenyl oxalate ester and a fluorescent dye. The chemical
compounds are kept separated in the light stick in two chambers. The phenyl oxalate
ester and dye solution fills most of the plastic stick itself. The hydrogen peroxide
solution is contained in a small, fragile glass vial in the middle of the stick. The
“snapping” or bending action breaks the glass vial and allows the chemicals to mix.
The chemicals immediately react to one another, and the atoms begin emitting light.
The particular dye used in the chemical solution gives the light a distinctive color. The
chemical reaction may last for a few minutes to a few hours to even a few days
depending on the formulation. Most light sticks found in the stores will last for a few
hours. As you discovered in this activity, temperature can speed up or slow down the
rate of the reaction. If you heat the solutions, the extra energy will accelerate the
reaction, and the light stick will glow brighter. However, the light stick will glow for a
shorter amount of time. If you place the light stick in cold water, the reaction will slow
down, and the light will dim. So, if you want to preserve your light stick for the next day,
put it in the freezer. The cold temperature will not stop the reaction, but it will slow
down the reaction until you warm up the light stick.
Additional Info
What… you want more information? Glowing things are sorted into categories or
groups that help us understand how they work.
Luminescence
Luminescence is cool (pun intended!) It’s true. Things that are said to “luminesce”
usually do so without needing or producing heat. You might think of it as “self-
generated” light. This category of glowing stuff is divided into the following even
smaller groups: fluorescence, phosphorescence, and bioluminescence.
Fluorescence
This type of luminescence occurs when some form of radiation, such as light, causes
an object to glow. For example, fluorescent papers and poster boards glow in the
daylight. They may seem to glow even brighter under black light (ultraviolet), but in
either case, as soon as the light is removed, the glow stops. Fluorescent things do
not glow in the dark all by themselves – they require some other form of energy such
as ultraviolet light to “excite” them.
Phosphorescence
Phosphorescence is just like fluorescence, except that the glow continues even after
the light used to excite it is removed. “Glow in the dark” toys phosphoresce brightly in
total darkness after being “charged” or excited by ordinary white or ultraviolet light.
Chemiluminescence
Sometimes a chemical reaction can produce light without producing heat. When that
happens, we call it chemiluminescence. Light sticks contain chemicals that when
mixed produce nearly any color of light.
Bioluminescence
This is a particular kind of chemiluminescence. Fireflies, certain fungi, various fish,
and some bacteria can produce light all by themselves. When such living things
produce light, it’s called bioluminescence.
Electroluminescence
Perhaps the best example of electroluminescence is lightning. When high voltage
electricity passes through a gas, the gas can become excited and glow. In the case of
lightening, the electrical spark passes through the air causing it to glow brightly.
Neon signs are also examples of electroluminescence. In this case, high voltages (e.
g. 12,000 volts, alternating current) are passed through a glass tube containing neon
gas. When the neon gas becomes excited, it produces a bright orange glow.
Sometimes argon gas is used instead of neon. The argon produces a blue glow.
Fluorescent tubes, such as those used in overhead light fixtures, use a combination
of electroluminescence and phosphorescence to make them work. A white coating
called a phosphor covers the inside of the glass tube. The high voltage makes the
gas glow, which in turn, excites the phosphor producing pleasant, white, room light/
Triboluminescence
Sometimes light is produced when objects (such as rocks or sugar crystals) are
broken, scratched, or pulled apart. This phenomena can be most easily observed
when you bite a Wintergreen Lifesavers… in the dark. Try it! Put a Wintergreen
Lifesaver (it must be this kind) in your mouth. Turn off the lights and stand in front of a
mirror. Bite the Lifesaver and look for the “spark” in your mouth. If you’re lucky enough
to break apart one of the Wintergreen favoring crystals, you’ll see a spark. Very cool!
Experiment From Steve Spangler Science
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