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Matter and MixturesAll 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 matter—solids, 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, it 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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vaporization

condensation

subl

imat

ion

subl

imat

ion

melting

solidification (freezing)

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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 don’t settle into layers we call the homogeneous mixture a solution.

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A heterogeneous mixture has large clumps of particles that don’t 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 don’t 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.

Substance Solubility (g/100g of water at 0°C)

Baking soda 6.9

Canola oil Insoluble

Ethyl alcohol Unlimited

Limestone 0.0007

Oxygen 0.007

Salt 35.7

Sugar 179.2

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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

Water out

Condenser

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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.

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Crude oil is separated into different chemicals in a process called fractional distillation. The crude is heated to about 400°C 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.

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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 PropertiesA 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 fluid’s 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

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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

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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.

Heating a Liquid Flow Rate Viscosity

Heating a Gas Flow Rate Viscosity

Cooling a Liquid Flow Rate Viscosity

Cooling a Gas Flow Rate Viscosity

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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.

V

mD

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 fast—they 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.

Substance Density (g/mL) Substance Density (g/mL)

Hydrogen 0.000009 Styrofoam™ 0.005

Helium 0.0002 Cork 0.24

Air 0.0013 Sugar 1.59

Oxygen 0.0014 Salt 2.16

Carbon Dioxide 0.002 Aluminum 2.70

Water 1.00 Iron 7.87

Seawater 1.03 Lead 11.34

Mercury 13.55 Gold 19.32

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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.

lw

h

r

h

r

h

a

b1

b2

hwlV

hrV 2

3

3

4rV

hbb

aV

2

21

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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.

V

mD

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.

Dense hull

Large volume of air trapped.

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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 Principle—the 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 car’s 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 PressureWhen 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).

A

FP

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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An air bag absorbs the force of your body impacting and slows you down more safely in high speed car crashes.

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.

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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 don’t 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 (CFC’s) 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.

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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.

Pam

101

102

P

NP

A

FP 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.

F

FA

FP

Nm

Pa

404

102

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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.