Matter and Mixtures

1
Matter and Mixtures
All of our physical world is made of matter.
Matter is anything that occupies space and has
mass. Over time, we have developed the idea that
every large lump of matter is made out of tiny
particles invisible to the human eye. The idea
that matter is is called the particle theory of
matter. The particle theory states that all
matter is made from particles, different
particles have different properties, particles
are constantly in motion.
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We can classify matter into 3 broad categories
called states of mattersolids, liquids, and
gasses. A solid has a definite shape and
volume. A liquid has a definite volume but no
definite shape. A gas has neither a definite
volume or shape.
Gas
Liquid
Solid
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There are attractive forces between particles.
In a solid, the attraction between particles is
strong so the matter holds its shape. The
particles are still moving, but they are not able
to slide past each other. They just vibrate.
In a liquid the attractive forces are not as
strong. The particles are able to move past each
other and slide around. The forces are strong
enough to keep the particles from flying away.
In a gas, the attraction between particles is so
weak that they fly in every direction filling the
container that they are held.
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As a solid is heated, the particles begin to move
more quickly. The attraction between them is
reduced and they begin to slide past each other.
This is called melting. If heating is
continued, the particles gain even more energy
and begin to fly away from each other in all
directions. This is called vaporization.
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The reverse process can happen as well. A gas
can be cooled so that the particles loose energy.
The attractive force pulls them together making
a liquid. This is called condensation. Dew on
leaves in the morning is an example of
condensation.
If cooling continues, eventually the particles
slow down enough that they are strongly attracted
to each other. This is called freezing or
solidification. Ice form is an example of the
solidification of water.
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Dry ice is called dry because when it heats up,
id does not make a liquid. Instead the particles
jump very energetically so that a gas is formed
without a liquid. This is called sublimation.
The reverse process is necessary to make dry ice
from carbon dioxide gas. When a gas changes
directly to a solid, the process is also called
sublimation.
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sublimation
vaporization
sublimation
condensation
solidification (freezing)
melting
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As well as classifying matter as solids, liquids,
and gasses, we can classify matter as either a
mixture or a pure substance. A pure substance is
made from only one type of particle. These
specific particle types give the substance its
physical characteristics such as odor, color,
hardness. A mixture contains two or more
substances.
A homogeneous mixture has two substances where
the particles are blended completely. To the
eye, the mixture appears to be pure substance.
When the particles stay intermixed and dont
settle into layers we call the homogeneous
mixture a solution.
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A heterogeneous mixture has large clumps of
particles that dont fully separate and get
intermixed with the other substance.
Some mixtures are in-between homogeneous
solutions and heterogeneous mixtures. A
suspension has clumps that stay floating.
Filtering a suspension will usually separate the
particles. A colloid has very small clumps that
almost make a solution. The clumps are so small
that they pass through most filters. Milk is an
example of a colloid. The clumps of particles
can even be held separate with an emulsifying
agent. When such an agent is used, an emulsion
is created (like mayonnaise).
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A mixture that is obviously heterogeneous is
called a mechanical mixture. A mechanical
mixture has separate parts called phases. These
phases can be separated into layers that are
distinct and visible. Oil forming layers in
water is another mechanical mixture with visible
phases.
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When we put sugar into water, a homogeneous
mixture results. The sugar particles are
completely separated from the clumps of other
sugar particles. This process is called
dissolving. The attractive forces between the
sugar particles and the water particles is strong
enough to pull the sugar particles away from the
main clump.
In fact, when water vaporizes, the water
particles are being dissolved into the air.
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This pill is being dissolved in water. The pill
is called the solute because it is the substance
being dissolved. The water is called the solvent
because it is the substance that is doing the
dissolving. In general, the solvent is in much
higher quantity than the solute.
Another way to say that the pill dissolves in
water is to say that the pill is soluble in
water. If a particular solute is soluble in a
solvent, that means that the solute will dissolve
in the solvent and make a homogeneous solution.
For example, nail polish does not dissolve in
water, but if we use a different solvent like
acetone (nail polish remover) the polish does
dissolve.
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On Earth, water is the most common solvent. Most
animals and plants need water to dissolve
nutrients to help carry them through the body.
Our blood is over half water. Water will
dissolve anything given enough time. So, why
dont we dissolve away from the water in our own
bodies? The rate of dissolving for many
substances is very slow. Even rocks will
dissolve in water if given a few million years.
We can speed up the process of dissolving by
agitation (mixing) or by heating the solvent.
Both agitation and heating will increase the
speed of the solvents particles and allow them to
break up the solute faster.
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According to the particle theory, every pure
substance is made from different particles with
different properties. This means that some
particles have a strong attraction with each
other and different particles may have weak
attractions. This means that some substances are
more soluble in different solvents that others
because their particles break away more easily.
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When a particular solvent has dissolved as much
solute as possible, the homogeneous mixture is
called saturated. A saturated solution will
still have some visible solid not yet dissolved.
If the solvent can still dissolve more solute,
the solution is said to be unsaturated. The
point of saturation will define the solubility of
the solute in the solvent. It is possible to go
beyond the saturation point.
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A heated solvent will dissolve more solute than a
cool solvent. If a heated solvent is saturated
and then slowly left to cool, the amount of
solute in the cool solvent is beyond to
saturation point. The mixture is said to be
supersaturated. With any small disturbance, like
adding a small piece of solid solute, crystals of
solute will form. This is called crystallization.
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The fact that solvents have different
solubilities with different solutes is very
helpful to us. When we get a stain on our
clothes, the stain is usually insoluble in water.
By using a detergent, the particles of the stain
can be removed. The difficulty is that often a
solvent that removes the stain will also remove
the pigment that gives your clothes their color.
Therefore, the trick is try to find a detergent
that dissolves the stain but not the pigment.
Restoring artwork is particularly difficult.
Oils and dirt over time collect on the oil
painting. It is difficult to remove only the
dirty oil and leave behind the paint. The left
side of this painting has been cleaned.
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Separating mechanical mixtures is usually quite
simple. Most of us can usually pick out the
cashews from a bowl of mixed nuts and gravy
separators can easily skim off oil.
Suspensions like coffee are easily filtered to
take out the tiny solid clumps floating in the
liquid.
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Separating a homogeneous solution is much more
difficult. One of the most basic techniques of
purifying water from dissolved solutes is called
distillation. During this process, a homogeneous
mixture is heated vaporizing some of the solvent.
The vapor rises and is then condensed in a
special tube called a condenser. The solvent
becomes liquid again and is recollected. The
result is a pure substance.
Water in
Condenser
Water out
20
If necessary, solar energy can be used to
evaporate water. The vapor rises, hits a clear
plastic sheet, condenses, and slides along the
edges to outside collection disks. A simpler
design uses a plastic wrap around a large
container and a smaller container inside. A
small pebble leads the condensed water to the
center container.
21
Crude oil is separated into different chemicals
in a process called fractional distillation. The
crude is heated to about 400C and then allowed
to pass through a large column. Lighter gases
are collected at the top while heavier liquids
fall further to the bottom. At different
locations, the fractions are collected and piped
away.
22
Solid mixtures also require a great amount of
work to separate. This is iron ore. An ore is a
rock contains a useful substance, like iron or
gold, and some other substances. To separate the
useful substance from the ore, first it is
crushed and then mixed with water to make a
suspension. Chemicals are added to dissolve the
iron but not other chemicals. The suspension is
filtered. The pure iron can then be extracted
from the water using chemicals and distillation.
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Fluid Properties
A fluid is any substance whose particles are able
to slide past each other. Liquids and gasses are
fluids because their particles flow easily past
each other. One of the main properties of a
fluid is the speed that it flows. This is called
the fluids viscosity. A thick fluid, like
ketchup, is more viscous and flows more slowly
than a thin fluid.
We measure viscosity by measuring the how fast
the fluid flows. This speed is called the flow
rate. Ketchup has a flow rate of about 40km per
year when poured from a bottle.
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The flow rate (and therefore viscosity) can be
altered. For example, if the fluid is heated, it
flows more quickly and hence has a lower
viscosity. If it is cooled, it will flow much
more slowly and have a much higher viscosity.
This can be very useful to the creation and
manufacture of many products such as Caramilk
bars. First chocolate is heated so it flows more
easily. Then it is poured into a mold. Caramel
is heated and poured into a similar smaller mold.
The caramel is then frozen solid. The little
caramel nuggets are then put into the soft
chocolate and covered with more heated chocolate.
The whole thing is allowed to cool and popped
out of the mold when it is solid.
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The reason why liquids flow faster when hot is
easily explained by the particle theory. As a
fluid is heated, the particles move more quickly.
If the particles move more quickly, they can
more quickly slide past each other. In exactly
the same way, if a liquid is cooled, the
particles flow more slowly. This explains why a
fluid that is cooled will flow more slowly.
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Different fluids have different viscosities.
This is because the particles in different fluids
have different properties. Again, this is part
of the particle theory. Water particles are
fairly small and are able to slip past each other
fairly easily. Heavy oils like tar and petroleum
jelly have much larger particles and bump into
each other more easily. This makes fluids with
larger particles have more internal friction
between the particles and decreases their ability
to slide past each other.
water
tar
27
Gasses are fluids as well. When can see super
cooled water vapor flowing along the ground when
we put dry ice into hot water. This is a cloud,
(just like the clouds in the sky) that flows
through the air.
However, gas particles move quite differently
than liquid particles. The attractive forces
between particles of a gas is very low since the
particles are so far apart. They move very
quickly in many random directions.
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Heating a gas will increase the speed of the
particles however, it will also increase the
randomness of the particle direction. This is a
little different than a liquid. Particles in a
liquid for the most part stay close to each
other, so if some start moving one direction,
most of the rest start moving the same direction.
This is important when looking at flow rate and
viscosity because the flow rate measures the
speed of the net movement of the particles.
Cool liquid
Hot liquid
29
To increase the flow rate of a gas, we need to
try to make the particles stay closer together so
they flow the same direction. By cooling a gas,
we are able to keep the particles closer together
and increase the flow rate. This means that
cooling a gas decreases the viscosity. In the
opposite way, heating a gas makes the particle
motion more random, decreases the flow rate and
thus increase viscosity.
30
Particles in a fluid are able to flow past each
other. This means that there is space between
the particles. To measure how crowded the
particles of a fluid are, we measure density. We
cannot easily measure the space between the
particles. But we could take a particular volume
of a substance and measure its mass. This gives
us a formula for density.
In the formula, d is the density, m is the
mass in grams, and v is the volume in cm3. We
need to remember on more thing. 1cm3
1mL Because particles have different sizes and
masses, different substances will have different
densities.
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Solids tend to have the largest densities. This
is because their particles are so close together.
In a fluid, like air, there is a very low
density. As a plane flies through the air, the
gas particles are pushed aside and solid metal
glides through.
This is one of the reasons planes can fly so
fastthey travel through very thin air.
Boats however travel through more dense water.
The water particles are still pushed aside but it
takes greater effort. Even very powerful boats
cannot travel as fast as a plane.
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Comparing densities can be difficult. Since
water is so plentiful and common, 1mL of water
was assigned the mass of 1gram. Therefore, the
density of water is 1g/mL. Compare this to other
substances.
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Calculating density is much more difficult than
you might think. First we need to know the mass
of an object. To measure the mass, we need to
use a balance. If we use a scale, we measure the
weight of the object. The weight is the force
due to gravity pulling down. The mass is
measured by the balance because the objects mass
needs to counteract the weights on the balance.
So we can use the weight of the object on a
balance to measure the mass of the object.
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Measuring the volume of an object can be very
tricky as well. Most objects are not regular
shapes that we have formulas for to calculate the
volume.
r
h
w
l
b2
r
a
h
h
b1
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But most real life objects only resemble these
shapes. If we want more accurate calculations we
need to find the volume of very odd shapes.
Measuring the volume of an odd shaped object is
almost impossible by calculation. The
displacement method is an easy way to find the
volume.
If the object sinks in water, we can measure a
volume of water, then drop the object into the
container. The water level will rise because the
particles are displaced. The difference in the
water levels from before and after will give you
the volume.
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Not all objects will sink however. If they do,
we can sink them in fluids with a smaller density
or push them down with some object with a known
volume. The ability to keep an object floating is
called buoyancy. An object floats due to a
buoyant force that works against gravity. The
existence of a buoyant force can be explained
using the particle theory. Particles in a fluid
are still attracted to each other. Pushing them
aside requires some force. When an object is
sinking, gravity is providing the force downward.
The attractive forces between particles resist
this force.
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A dense fluid should resist more strongly and
therefore demonstrate a stronger buoyant force.
This can actually be seen using very dense fluids
like mercury.
Mercury is an extremely dense liquid metal.
Iron, bricks, or billiard balls float easily in
mercury. It is toxic however and should not be
handled.
Water is not nearly as dense as mercury. How is
it then that boats made from iron, steel, or
aluminum are able to float?
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Recall that there is a formula for the density.
Air has a very low density (almost 0).
Therefore, if an object is able to trap a large
quantity of air then it should be able to lower
its density. If the average density of the
object in the water is less than 1, then the
object should float. Look at the cross section
of a boat floating in water.
Large volume of air trapped.
Dense hull
39
A submarine can alter the average density of the
ship by pumping water into large holding tanks
called ballasts. To make the submarine rise, the
water is pumped out and air pumped into the
ballasts.
Fish use a swim bladder that they fill with air
to make them float. They push the air out to
increase density and sink.
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The concept of buoyant force is not a new one.
Archimedes at around 200 BC discovered that a
sinking object will disperse a volume of water
equal to its own volume. He theorized that this
was why a boat could float despite being filled
with heavy objects.
An object with a volume great enough to float its
mass is said to have neutral buoyancy.
Archimedes summarized his findings about buoyancy
and came up with a way to calculate the buoyant
force. This is called Archimedes Principlethe
buoyant force acting on an object equals the
weight of the fluid displaced by the object.
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A hydrometer is another way to measure the
density. This one measures the salinity (amount
of dissolved salts) in aquarium water.
This hydrometer is used to test the quality of a
cars antifreeze. Antifreeze that has degraded
due to heat and age will be less dense and less
able to keep the car from freezing or overheating.
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Fluids Systems and Pressure
When you exert a force against an object you are
applying pressure to the object. Pressure is the
amount of force applied divided by the area that
the force is applied over. We use the following
formula to relate the pressure (P) to the force
(F) and the area (A).
The unit of pressure is called a pascal (Pa)
named after the scientist Blaise Pascal. 1
pascal is equal to the 1 Newton of force exerted
over an area of 1 m2. This is about the weight
of a small apple spread over a 1 m2 area. This
is very small so we usually use the kilopascal
(kPa) to measure pressure.
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If a gas is enclosed in a container, a force can
be applied to the gas. This causes compression
of the gas. The particles are forced into a
smaller volume reducing the spaces between the
particles.
The force exerted is needed to compress the
spaces between the particles. Since gasses have
a large amount of space between particles, they
are able to absorb a lot of force and compress
very significantly. Liquids and solids do not
compress very well
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We use compression of gasses every day. This
high jump mat is full of air and cushions your
fall when you land after your jump.
An air bag absorbs the force of your body
impacting and slows you down more safely in high
speed car crashes.
45
The atmosphere of the Earth is actually quite
thick (160km). Gravity keeps the atmosphere
close to the surface. The weight of the air
exerts pressure on all of the objects on the
ground. In the same way that we can feel the
difference in pressure as we dive deeper into a
pool of water, the air pressure increases as you
get closer to sea level. The reason we dont get
crushed from the pressure of the atmosphere is
that we have an equal pressure inside of us
pushing outward. Moving suddenly from one
altitude to another causes pressure differences.
Our ears popping is one effect of pressure
differences between the atmosphere and inside our
bodies.
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This mercury barometer measures the atmospheric
pressure. The large pool of mercury experiences
pressure from the atmosphere. The liquid is
forced up the vacuum tube against the force of
gravity. The height of the mercury in the tube
is then measured. Normal atmospheric pressure
pushes the mercury to a height of 760 mm.
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Pressure can be stored in a container and
released at controlled times when we want to
exert a force. A can of whipped cream is an
aerosol. It contains a gas under pressure that
when released through the nozzle, pushes and
cream out. Aerosol products are common in
cleaners, hair mousse, and spray paint.
Chlorofluorohydrocarbons (CFCs) uses to be used
as the gas under pressure because these compounds
are very non-reactive.
It was found later that CFC can react in the
upper atmosphere and causes breakdowns in the
Ozone layer protecting Earth from UV radiation.
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It is possible to use pressure inside a closed
system. An air pump, for example, compresses air
and sends it through a nozzle using a set of
valves to control the direction of the flowing
air particles.
As the plunger is pushed down, air inside the
container is compressed. The valve at the bottom
is open and allows air to be pushed through the
nozzle. When the plunger is pulled up, the valve
at the bottom shuts and the top valve opens
allowing the atmospheric pressure to push air
back into the pump.
49
Liquids can also be made to flow in systems. In
many ways, liquids are more useful than gasses
since they do not compress as much as gasses.
Your car uses a liquid oil in the brake system to
stop the car. When pressure is applied to the
peddle, the force is transferred to the brakes on
the wheels. Image what would happen if the brakes
were filled with a gas instead of a liquid.
First the gas would need to be compressed
significantly and then the pressure would be
transferred to the brake pads. This would make
your brakes less responsive and would decrease
the stopping power of your car.
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A fluid system using pressure from liquids is
called a hydraulic. A hydraulic system uses the
relationship of force pressure and area. For
example, this hydraulic has two connected
plungers with different areas. If a force is
applied to the small plunger, pressure is created
throughout the system. The area of the large
plunger is much greater, therefore, the force is
much greater. This is because the pressure in
the system is constant.
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Imagine this example. The area of the left
plunger is 1m2 and the area of the right plunger
is 4m2. Then if 10N of force is applied to the
left plunger the pressure is found using our
formula.
Therefore, the pressure on the right side is also
10Pa. We find the force up on the right side
using the same formula again but this time we
know the pressure and the area is larger.
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This type of hydraulic system can be very useful
when we are trying to lift heavy loads. Pressure
in hydraulics like refinery pipes move liquids
from one location to another. Pumps are required
to make enough pressure to move the fluids
through.
Water slides also use hydraulics to move water to
the top of the slide. Gravity pulls the water,
and you, back down.
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Liquids are not the only fluids moved in pipes.
Natural gas is also pushed using special pumps
called compressors through pipes in the ground to
your home. A meter monitors how much gas runs
into the house and used. A gas system is called
a pneumatic system. A balloon can be though of
as a pneumatic system.