What Is It?
Section: __ Date: _________
Air and water are two materials with which everyone is familiar. We live at the
bottom of an ocean of air, called the atmosphere. Air surrounds our bodies every
minute of our lives, except when we are swimming or bathing. Air may be found in
almost every open hollow in all materials on the surface of the earth. There is air
also in many of the hollows and openings of the human body – for example, our ears,
mouth, nose and lungs. All animals breathe air, and if deprived of it, they die.
The waters of seas, lakes, rivers and streams cover three-quarters of the
earth’s surface. Air and water are two materials with which everyone is familiar.
The cells of which all living things are made are largely water. Water, given enough
time, will dissolve almost any substance. This is important, because the materials
that nourish living things are dissolved in water. This water makes up the main
part of the blood of animals and the sap of plants, the two fluids that carry
nourishing materials to the cells of living things.
The two major gases, nitrogen and oxygen, continually leave and then return to
the atmosphere in endless processes, or cycles. Nitrogen from the air that
penetrates the upper layers of the soil is changed by certain bacteria to chemical
compounds that can be used as nourishment by plants. The plants may be eaten by
animals that excrete compounds of nitrogen, which are decomposed by other
bacteria in a process that eventually releases nitrogen to the air. The released
nitrogen now may re enter the soil—as the nitrogen cycle continues, over and over
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Oxygen is breathed by animals that exhale carbon dioxide. Plants absorb
carbon dioxide from the air and give off oxygen that is again breathed by animals –
as the oxygen cycle continues endlessly.
1. Explain the nitrogen cycle
2. Explain the oxygen/carbon dioxide cycle
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How Can You Show Some Materials Hold Air?
Gently drop a clod of earth into a pot or glass full of water. Note the bubbles
that arise. These bubbles are air that was held in the spaces between the
particles of earth. The fact that air can penetrate into the soil is very important
to the growth of plants. Probably the most needed substance for plant
nourishment is the chemical element nitrogen. Four-fifths of air is nitrogen. Yet
plants cannot obtain nitrogen directly from the air. However, certain bacteria that
live in the soil can remove nitrogen from the air and change the nitrogen to a form
that can be used by plants. Thus, you can see why it is important that air
Into some clean water put a piece of brick and a smooth, well-washed pebble.
Note that air bubbles arise from the piece of brick, but not from the pebble.
There are many air spaces in brick, but none in solid stone. This shows that not all
substances are penetrated by air.
Place a clean glass of water in the sun. Look at it about an hour later. Do you
see the bubbles on the inside of the glass? They are air bubbles. Pour the water
from the glass into a pot, set the pot on a stove, and boil the water. Now, many
more bubbles arise from the water, showing that more air was in the water. You
cannot boil all the air out of the water, because more is entering the water as you
boil some out.
How Can You Prove Air
Is Really A Kind Of Matter?
If we have a box in which we cannot see anything, we say the box is empty.
After we drink all the water in a glass, we say there is nothing in the glass. Yet,
it is not true that there is nothing in the box and glass – both are full of air.
Although we cannot see air, we must not believe that air is nothing at all. Air is
matter. Like all matter, it takes up space and has weight.
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Matter is anything that has mass and takes up space. So, in order to prove that
air is matter, we need to prove that air has mass and takes up space. It's easier to
prove that air takes up space, so let's do that part of the problem first.
Lower a drinking glass, mouth downward, into a large jar or pot three-quarters
full of water. Note that the water pushes only a little way up into the glass. What
keeps the water from rising all the way up into the glass? Something must be
taking up the space inside the glass and thereby keeping the water out. It is air
that occupies the space in the glass.
Although air has mass, a small volume of air, such as the air in the balloons,
doesn't have too much. Air just isn't very dense.
Obtain two balloons of the same size. Blow them up to the same size, and tie
their necks so that the air will not escape. After tying each balloon, leave about a
foot and a half of string free, and tie a loop at the end of each string.
Balloons are a great example of how the pressure (force per unit area that a gas
exerts on the walls of a container) and the volume (the space that a particular
quantity of a gas occupies at a specific temperature and pressure) of a gas are
interconnected. When you blow up a balloon, you exert pressure on the inside walls
of the balloon. When that pressure exceeds the outside air pressure plus the
pressure exerted by the latex itself, the balloon begins to expand. The pressure
inside a balloon is always a little higher than the surrounding air pressure, because
the latex is pushing back as the air inside pushes out. When a weather balloon rises
in the atmosphere, for example, the outside pressure decreases and the balloon
expands. Eventually, the inside pressure causes the balloon to burst.
Tie a string around the middle of a yardstick, and suspend it so that it swings
freely. Slip the loops at the ends of the strings that are attached to the balloons
over the ends of the yardstick, and adjust the balloons so that they balance the
yardstick. When the yardstick has stopped swinging, burst one of the balloons
with a pin. The other balloon will swing downward.
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Since both the full balloon and the burst balloon weigh the same, there must
be something on the side of the full balloon that pulls the yardstick down on that
side. This something is the air in the balloon. This proves that air has weight.
Expand on This!
Inflate balloons with different gases and weigh your results.
Air is mostly a mixture of oxygen and nitrogen, but it also contains smaller
amounts of other gases, such as carbon dioxide. That's the gas that is released
when you drop a stomach-acid neutralizer like Alka-Seltzer into water. Do you
think a balloon full of carbon dioxide will weigh more or less than a balloon full of
balloons of equal size
a flask that can hold some pressure
string or tape measure
a balance that weighs to the nearest .01 gram
Alka-Seltzer, broken into pieces small enough to fit through the mouth of
a) Pour about 150 ml of water into the flask.
b) Working as quickly as possible, drop in six Alka-Seltzer tablets.
Lightly stuff the mouth of the bottle with cotton and stretch the
open end of a balloon securely over the top of the bottle. (The cotton
allows the carbon dioxide through, but soaks up any splashed water.)
c) When the balloon is filled with carbon dioxide, or the tablets have
stopped fizzing, tie off the balloon and measure its circumference
with a string or tape measure.
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d) Inflate another balloon with air to the same circumference. (Two
spherical objects of the same circumference will have the same
e) Perform the balance experiment, again.
Pretend that you and your classmates are gas molecules. How is the inside of
your classroom like a balloon?
How could your group of gas molecules escape? Is it easy or hard to get out?
At absolute zero, you're packed all together in a corner of the room. As the
temperature goes up, you begin to vibrate and move around. Can you stay close as
the temperature increases?
Inflate two balloons to equal size. Place one in a pan of hot water and the other
in a pan of cold water. What happens? What will happen to equal-sized balloons in a
range of temperatures?
How Can We Demonstrate
Fill a drinking straw with water, and place your finger tightly over one end.
Turn the straw so that the open end points downward. Some water will run out, but
most will remain in the straw. What keeps most of the water from running out? It
is the atmospheric pressure that is pressing upward at almost 15 pounds per square
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Run enough water into a sink or large jar so that you can place a glass on its side
completely under water. Keeping the glass under water, turn it around so that its
mouth points downward. Raise the glass, until all but about half an inch of it is out
of the water. The glass remains full of water, even though it is upside down. What
keeps the water in the glass?
Atmospheric pressure on the surface of the water in the sink or jar pushes
water up into the glass. The weight of the air on the surface of the water in the
sink or jar is greater than the weight of the water in the glass. Thus the water is
held inside the glass at a level higher than the surface of the water outside the
The experiments you just performed are somewhat like the one performed by
the Italian physicist Evangelista Torricelli. He filled a long glass tub with water.
The tube was nearly 40 inches long and had a faucet at one end; the other end was
closed. Torricelli stood the glass tube upright in a tub of water, the faucet end
down. He then opened the faucet. Some of the water ran out the bottom of the
tube. The length of the column of water that was left was 34 inches. Torricelli
knew, then, the pressure of air on the water in the tub was enough to support a
column of water 34 inches high. He weighed the water in the tube and from this
weight he was able to calculate that, in order to hold up a column of water 34
inches high, the atmosphere had to press downward with a weight of nearly 15
pounds per square inch.
In this way, Torricelli was the first to discover atmospheric pressure.
Torricelli performed his experiment at sea level. If he had performed it on top of
Mount Everest, which is about six miles high, there would have been less air above
the tub to press on the surface of the water. As a result, he would have found
atmospheric pressure to be only a little more than six pounds per square inch.
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Barometer (Evangelista Torricelli)
In the early 1600s, Galileo argued that suction pumps were able to draw water from a
well because of the "force of vacuum" inside the pump. After Galileo's death, the Italian
mathematician and physicist Evangelista Torricelli (1608-1647) proposed another
explanation. He suggested that the air in our atmosphere has weight and that the force of
the atmosphere pushing down on the surface of the water drives the water into the
suction pump when it is evacuated.
In 1646 Torricelli described an experiment in which a glass tube about a meter long was
sealed at one end, filled with mercury, and then inverted into a dish filled with mercury, as
shown below. Some, but not all, of the mercury drained out of the glass tube into the dish.
Torricelli explained this by assuming that mercury drains from the glass tube until the
force of the column of mercury pushing down on the inside of the tube exactly balances
the force of the atmosphere pushing down on the surface of the liquid outside the tube.
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Torricelli predicted that the height of the mercury column would change from day to
day as the pressure of the atmosphere changed. Today, his apparatus is known as a
barometer, from the Greek baros, meaning "weight," because it literally measures the
weight of the atmosphere. Repeated experiments showed that the average pressure of
the atmosphere at sea level is equal to the pressure of a column of mercury 760 mm tall.
Thus, a standard unit of pressure known as the atmosphere was defined as follows.
1 atm = 760 mmHg
To recognize Torricelli's contributions, some scientists describe pressure in units of
"torr," which are defined as follows.
1 torr = 1 mmHg
On a sunny day, at sea
level, the weight of a 760-mm
column of mercury inside a
glass tube balances the weight
of the atmosphere pushing
down on the pool of mercury
that surrounds the tube. The
pressure of the atmosphere is
therefore said to be
equivalent to 760 mm Hg.
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How Can You Demonstrate
Force of Air Pressure?
We define matter as something which occupies space, is affected by gravity
and has weight. Make a vessel that won't collapse if there is no air inside of it.
Weigh the vessel when it is full of air. Then pump all of the air out and weigh the
vessel again. The difference in weight is the weight of the air.
In 1654, a German scientist, Otto von Guericke (Goo-er-ick), amazed everyone
by showing how much force could be exerted by the pressure of the atmosphere.
He used two iron hemispheres, each of which was about 22-inches in diameter.
Their rims were carefully ground smooth and covered with grease. He put the rims
together, and, with a vacuum pump he had invented, removed the air inside the
hollow sphere. So great was the air pressure on the outside that it took 16 horses,
eight on each side, to pull the hemispheres apart.
You can perform an experiment like that of von Guericke. You will need two
plungers of the kind that are used to force water through drains. You will also
need a friend to help you. Thoroughly wet both plungers. Ask you friend to sit in a
chair and hold the plunger handle, the rubber cup upward. Place the cup of your
plunger upon the other one, and slowly and carefully push down until most of the air
has been expelled from the plunger cups. Now, each of you grasp a handle, and see
how difficult it is to pull the plungers apart.
If you have only one plunger, place it on a smooth wet surface, and push down
hard. You will see how strongly you have to pull in order to pull it free. All the
force holding the plunger to the surface is due to atmospheric pressure.
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Earth, according to one scientific
theory, is believed to have formed about 5
billion years ago.
In the first 500 million years a dense
atmosphere emerged from the vapor and
gases were expelled during degassing of the planet's interior. These gases may
have consisted of hydrogen (H2), water vapor (H20), methane (CH4), and carbon
oxides. Prior to 3.5 billion years ago the atmosphere probably consisted of carbon
dioxide (CO2), carbon monoxide (CO), water (H2O), nitrogen (N2), and hydrogen.
The hydrosphere (water world) was formed 4 billion years ago from the
condensation of water vapor, resulting in oceans of water in which sedimentation
(from our rock unit) occurred.
The most important feature of the ancient environment was the absence of
free oxygen. Evidence of this is hidden in early rock formations that contain many
elements, such as iron and uranium. Elements in this state are not found in the
rocks of mid-Precambrian (a fancy word meaning early age of Earth) and younger
ages, less than 3 billion years old.
One billion years ago, early aquatic organisms (water critters) called blue-green
algae began using energy from the Sun to split molecules of H2O and CO2 and
recombine them into organic compounds and molecular oxygen (O2). This solar
energy conversion process is known as photosynthesis. Photosynthesis simply means
plants use sunlight, carbon dioxide, and a molecule in their systems, called,
Chlorophyll, to make food. Plants are the only organisms on Earth that can make
their own food. During this process, the waste produced from this procedure is
expelled back into the air – that waste product is called, oxygen (02).
Some of the photosynthetically created oxygen combined with organic carbon
to recreate CO2 (carbon dioxide) molecules. The remaining oxygen accumulated in
As oxygen in the atmosphere increased, CO2 decreased.
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Okay, first, let’s understand oxygen. The chemical name is 02. That means,
there are two oxygen atoms bonded together to form a molecule. A molecule is
two or more atoms bonded together. So, in reality, oxygen is not a single atom,
but, rather, two atoms joined together to make a molecule that we call, oxygen, it’s
real name is, dioxide. Di=two, and oxide=oxygen atom.
High in the atmosphere, some oxygen (O2) molecules absorbed energy from the
Sun's ultraviolet (UV) rays and split to form single oxygen atoms. These atoms
combining with remaining oxygen (O2) to form ozone (O3) molecules, which are very
effective at absorbing UV rays. The thin layer of ozone that surrounds Earth acts
as a shield, protecting the planet from UV light.
The amount of ozone required to shield Earth is believed
to have been in existence 600 million years ago. At this
time, the oxygen level was approximately 10% of its present
atmospheric concentration. Prior to this period, life was
restricted to the ocean. The presence of ozone enabled
organisms to develop and live on the land. Ozone played a
significant role in the evolution of life on Earth, and allows
life as we presently know it to exist.
Nitrogen - 78% - Dilutes oxygen and
prevents rapid burning at the earth's
surface. Living things need it to make
proteins. Nitrogen cannot be used directly
from the air. The Nitrogen Cycle is
nature's way of
supplying the needed
nitrogen for living
B. Oxygen - 21% - Used by all living things. Essential for
respiration. It is necessary for combustion or burning.
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C. Argon - 0.9% - Used in light bulbs.
D. Carbon Dioxide - 0.03% - Plants use it to make oxygen. Acts as a blanket and
prevents the escape of heat into outer space. Scientists are afraid that the
burning of fossil fuels such as coal and oil are adding more carbon dioxide to the
E. Water Vapor - 0.0 to 4.0% - Essential for life processes. Also prevents heat
loss from the earth.
F. Trace gases - gases found only in very small amounts. They include neon, helium,
krypton, and xenon.
1. Within the first 500 million years of Earth’s existence, certain gases
spewed out of the molten rock. Name those gases.
2. Theory has it the first atmosphere that enveloped the Earth comprised of:
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3. What does Precambrian mean?
4. What was the name given to the first aquatic critters on Earth?
5. Describe photosynthesis.
6. What is a molecule?
7. Due to the intense ultraviolet energy from the Sun, organisms were
restricted to living deep in the ocean. What happened that permitted these
organisms to come to the surface of the ocean?
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8. Name the gases most prevalent in today’s atmosphere, and, give at least one
characteristic of each of those gases.
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