Years 7-8 Solids, Liquids Gases

keep it simple sciencePhotocopy Master Sheets

Years 7-8

Solids, Liquids&

GasesDisk filename = “03.Matter”

Usage & copying is permitted according to theSite Licence Conditions

only

ABN 54 406 994 557

PO Box 2575PORT MACQUARIE NSW 2444

(02) 6583 4333 FAX (02) 6583 9467www.keepitsimplescience.com.au [email protected]

kkeeeepp iitt ssiimmppllee sscciieennccee®

2

Topics Available

Year 11-12 Science CoursesBiologyPreliminary CoreLocal EcosystemPatterns in NatureLife on EarthEvolution Aust. BiotaHSC CoreMaintain. a BalanceBlueprint of LifeSearch for Better HealthOptionsCommunicationGenetics:Code Broken?

ChemistryPreliminary CoreChemical EarthMetalsWaterEnergyHSC CoreProduction of MaterialsAcidic EnvironmentChem.Monit.&MngmentOptionsShipwrecks, Corrosion...Industrial Chemistry

Earth & Envir.Science

Preliminary CorePlanet Earth...Local EnvironmentWater IssuesDynamic EarthHSC CoreTectonic ImpactsEnvirons thru TimeCaring for the CountryOptionIntroduced Species

PhysicsPreliminary CoreWorld CommunicatesElectrical Energy...Moving AboutCosmic EngineHSC CoreSpaceMotors & GeneratorsIdeas to ImplementationOptionsQuanta to QuarksAstrophysics

Year 7-8 General ScienceDisk Filename Topic Name01.Energy Energy02.Forces Forces03.Matter Solids, Liquids & Gases04.Mixtures Separating Mixtures05.Elements Elements & Compounds06.Cells Living Cells07.Life Living Things08.LifeSystems Plant & Animal Systems09.Astronomy Astronomy10.Earth The Earth11.Ecosystems Ecosystems

Year 9-10 General ScienceDisk Filename Topic Name12.Waves Wave Energy (inc. Light)13.Motion Forces & Motion14.Electricity Electricity15.Atoms Atoms & Elements16.Reactions Compounds & Reactions17.DNA Cell Division & DNA18.Evolution Evolution of Life19.Health Health & Reproduction20.Universe The Universe21.EarthScience Earth Science22.Resources Resources & Technology

Site Licence ConditionsA school (or other recognised educationalinstitution) may store the disk contents inmultiple computers (or other data retrievalsystems) to facilitate the following usages ofthe disk contents:

• School staff may print unlimited copies onpaper and/or make unlimited photocopies atone school and campus only, for use bystudents enrolled at that school and campusonly, for non-profit, educational use only.

• School staff may use the disk contents tomake audio-visual displays, such as viacomputer networks, or by using dataprojectors or overhead projectors, at oneschool and campus only, for viewing bystudents enrolled at that school and campusonly, for non-profit, educational use only.

• School staff may allow students enrolled atthat school and campus only to obtaincopies of the disk files and store them ineach student’s personal computer for non-profit, educational use only.

IN SUCH CASE, THE SCHOOLSHOULD MAKE PARTICIPATING

STUDENTS AWARE OF THESE SITELICENCE CONDITIONS AND ADVISE

THEM THAT COPYING OF DATAFILES BY STUDENTS MAY

CONSTITUTE AN ILLEGAL ACT.

• In every usage of the disk files, the KISSlogo and copyright declaration must beincluded on each page, slide or frame.

Please Respect Our Rights Under Copyright Law

All Topics Available as PHOTOCOPY MASTERS and/or KCiCPhotocopy Masters (PDF files)

Black & White, A4 portrait-orientationfor clear, economical photocopying.

KCiC = Key Concepts in ColourFull colour, formatted for on-screen studyand data projection. PDF + Powerpoint®

Powerpoint is a trademark of Microsoft Corp.

Usage & copying is permitted according to the Site Licence Conditions only

keep it simple science®

Year 7-8 Topic 3 Solids, Liquids & Gasescopyright © 2008 keep it simple sciencewww.keepitsimplescience.com.au

3

“Mind-Map” Outline of TopicThis topic belongs to the branch of Science called “Chemistry”.

Chemistry is the study of matter and materials. Chemistry looks at the propertiesof substances, and how substances can change into new forms.

The Moving Particle

Model

Changeof State

Explained

AirPressure

Calculations

Density & the

Particle Model

Density &Heat

Expansion

Density &

Flotation

Heat Expansion

Properties ofMatter Changes of

State

Solids, Liquids&

Gases

The States of Matter

GasPressure

Density

Effects ofHeat



4


Make your own “Mind-Map” TITLE PAGE.Cut out the boxes. Sort them into an appropriate lay-out on a page of your

workbook, then glue them down. Add connecting arrows and colour in.

The Moving Particle

Model

Changeof State

Explained

AirPressure

Calculations

Den

sity

&

the

Part

icle

Mod

el

Density &Heat

Expansion

Density &

Flotation

Heat Expansion

Properties ofMatter

Changes of State

Solids, Liquids&

Gases


GasPressure

Density

Effects ofHeat

The Moving Particle

Model

Changeof State

Explained

AirPressure

Calculations

Den

sity

&

the

Part

icle

Mod

el

Density &Heat

Expansion

Density &

Flotation

Heat Expansion

Properties ofMatter

Changes of State

Solids, Liquids&

Gases


GasPressure

Density

Effects ofHeat

Make your own “Mind-Map” TITLE PAGE.Cut out the boxes. Sort them into an appropriate lay-out on a page of your

workbook, then glue them down. Add connecting arrows and colour in.


5

Solid, Liquid, Gas

Testing Compressibility

The Earth is mostly solid rock. The oceans are liquid water. The air we breathe is a gas.

All around us are many different substances, but when we come to study the science ofmatter, one simple starting point is that all substances are either solid, liquid or gas.




SolidsGenerally,

• have a definite shape.

• are hard.

• cannot be compressed.(squashed into a smaller space)

A solid made of grains, like drysand, has no definite shape andcan flow like a liquid. However,each grain is hard, has a definiteshape and cannot be compressed.

LiquidsGenerally,

• have no definite shape.They take the shape of whatever container they are in.

• can flow, and be poured.

• cannot be compressed.

GasesGenerally,

• have no definite shape.They completely fill whatever container they are in.

• can easily flow and move.(e.g. when the wind blows)

• are easily compressed.

Liquids & Gases are both “fluids”; substanceswhich can flow and change shape.

One of the big differences between thestates of matter is whether or not asubstance can be squashed into asmaller space.

This property can be studied using asyringe, or even a bike pump.

Water

Outlet blockedwith a finger

You will find it impossibleto compress water

Push on theplunger

If you try again with the syringe filledwith air, you’ll find it very easy tocompress the gas.

Simplest definitions of the States of Matter

Solid = incompressible non-fluidLiquid = incompressible fluid

Gas = compressible fluid

Air

A gas can be easilycompressed




6

Changes of StateMost pure substances can change their state from solid to liquid to gas, and backagain. When this happens, it is still the same substance, but in a different state.

LEARN THE NAMES FOR EACH CHANGE.

Examples of Changes of State

Solid Liquid Gas

meltingvaporisation (or boiling)

freezing (or solidification)condensation

sublimation

Solid water is ice. Ice melts to liquid water.

Liquid water boilsand vaporisesto “water vapour”.

As the vapourcools, it

condensesback to liquid.

Note that watervapour is an

invisible gas. If youcan see a cloud of

“steam”, it isactually a cloud of

tiny little liquiddroplets. Clouds in

the sky are alsomade of tiny liquid

droplets whichhave condensed

from water vapour.Liquid water can freeze

to ice.

Ice is solid water, but it is still the substance water.

Water vapour is a gas, but it is still water.

When a substance changes its state, it remains the same substance. It can change its state over and over again, but it is still the same stuff.

Sometimes it is possible for asubstance to change fromsolid to gas, or from gas tosolid. In either direction thischange is called sublimation


7

The Moving-Particle Model

Scientific Models

How can the properties of solids, liquids and gases be explained?

We believe that all substances are made of tiny lumps of matter we call particles. Each particle can be imagined to be like a tiny solid ball, too small to see.

Solid Liquid Gas



The particles are tightlypacked together.

This explains why solidsare incompressible.

They are held firmly inplace by forces of

attraction.

This is why solids arehard with a fixed shape.

Although the particles arefixed in place, they

vibrate and jiggle arounda bit.

The particles are tightlypacked together.

This explains why liquidsare incompressible.

The particles are able tomove around, bumpingand jostling each other.

This explains why liquidshave no fixed shape, and

take the shape of theircontainer.

This also explains howthey can flow as a “fluid”.

The particles are farapart.

This explains why gasesare easily compressible.

It is easy to push theparticles closer together.

The particles are flyingin all directions at high

speed, colliding andbouncing away again.

This explains why theyhave no fixed shape, andtotally fill their container.

Notice that in every case the particles are moving.In solids, they only vibrate in one place. In liquids they move around

among each other. In gases they fly freely at high speed.

Is this description of solids, liquids andgases real? Well, yes, and no.

We have many good reasons to believethat all matter is made of small particlescalled atoms. Often they join together inlarger lumps called “molecules”.

However, we also know that atoms arenot solid ball-like particles, but aremade of many smaller pieces.

There are forces of attraction betweenatoms and molecules.

So overall, the description above ispartly true, but is not the full story.

Scientists often develop “models” ofthings that cannot easily be seen. Thishelps in understanding and explainingthe observed facts.

So long as the model explains things,and always remains totally in agreementwith what we can see and measure, thenit is useful, even if it is a simplification ornot quite the full story.

For now, ball-like “particles” will be our model of matter.




8

The 3 “states of matter” are a)....................,.......................... and .........................

Generally, solids are hard, with a definiteb)............................. and c).......................(can/cannot) be compressed.

Liquids have no definite shape, but take theshape of their d)............................... Liquids cane)............................ and be poured. Like solids,they cannot be f)........................

Gases have no shape, and completelyg).................. their container. They can flow andare easily h)..............................

When a solid turns to a liquid the change iscalled i)............................... The reverse change(liquid to solid) is calledj)..........................................

When a liquid turns to a gas the change iscalled k)...............................

The reverse change (gas to liquid) is calledl)..........................................

It is also possible for a solid to turn to gasdirectly, without going through them)............................. stage. This change iscalled n)..........................................

The “Moving o).......................... Model”states that all substances are made of tinyparticles.

In a solid, the particles arep)................................................................ andheld firmly in q)....................... The particlescannot move around, but canr)........................................ back-and-forth.

In a liquid, the particles are also verys)......................................................, but cant).........................................

In a gas, the particles are u).......................and are v)........................ at high speed.

Worksheet 1States of Matter, Particle Theory

Fill in the blank spaces

Worksheet 2States of Matter, Particle Theory

Briefly answer each question

Student Name.............................................

Student Name.............................................

1. Which feature of a gas:a) allows it to be easily compressed?

b) causes it to always fill its container?

2. Which two states of matter areconsidered to be “fluids”?

3. Which feature of a solid:a) makes it incompressible?

b) causes it to have a fixed shape?

4. Which feature of a liquid:a) allows it to change its shape and flow?

b) makes it incompressible?

5. Which two states of matter cannot beeasily compressed?

6. Name the change of state.a) gas to liquid ..................................

b) liquid to solid ....................................

c) liquid to gas ....................................


9

Moving Particles? What Makes Them Move?

Changes of State... Again

The answer is “Heat Energy”.

When you add heat energy to any substance, the particles in it do not get hotter... they get faster.When something cools down, the particles do not get any colder... they go slower.

The measurement we call “temperature” is actually a measure of how fast (on average) the particles are moving.

In a solid substance the particles cannot move around, but only vibrate. When a solid is heated, the particles vibrate faster, but still stay in their fixed place.

Note: The energy of a moving thing is called “Kinetic Energy”.The Moving-Particle Model is sometimes called the “Kinetic Theory (Model) of Matter”.



Moving particles in a substance.

Particles move faster.Temperature has increased.

Heat Energy added.

With a knowledge of what heat energydoes to particles, we can explain whathappens in a change of state.

MeltingParticles in a solid are

vibrating, but are held inplace by forces of

attraction.

Adding heat makes theparticles vibrate faster.

The forces between themare still there, but theparticles have more

energy so the forces arealmost overcome.

At a certain temperature(the “melting point”) theparticles break free fromtheir positions and begin

moving around. Theforces are still there, butunable to hold them. The

particles are still closetogether, but movingamong each other.

Heat Added

Heat Added

More Heat Added

More Heat Added

The solid has melted!

EvaporationParticles in a liquid are

close together, butmove around among

each other.

When heated, theparticles move faster.Even at relatively lowtemperatures, a few

particles have enoughenergy to fly off into thegas state. Some of theliquid is evaporating.

At a particulartemperature

(the “boiling point”) many of the particlesreach the speed to

evaporate. Bubbles ofgas vapour form withinthe liquid... the liquid is

boiling.


10

Heat ExpansionIt is an observed fact that substances expand (get bigger) as they get hotter, and contract (shrink) as they get cooler.

How does our Moving-Particle Model explain this?In a Solid... In a Liquid...

Investigating Heat Expansion

You may do some experiments, or seedemonstrations, of heat expansion.

When both arecold, the ball fitsthrough the ring.

When the ball isheated, it

expands andwon’t fit through.

When warmed up,the liquid expands,so it rises up in thenarrow glass tube.

This is the sameprinciple as athermometer



Particles in a solid arevibrating, but are held in

place by forces ofattraction.

Adding heat makes theparticles vibrate faster. As

they jiggle and pushagainst each other, theyare forced a little further

apart. This makes thesolid substance get biggerand occupy more space.

Heat Added Heat

Added

Particles in a liquid areclose together, but

move around amongeach other.

When heated, theparticles move faster.They collide faster andharder and push each

other away. Thiscauses the volume ofthe liquid to get bigger.The liquid expands and

occupies more space.

Very Important: Notice that the particles DO NOT expand.The particles force each other a bit further apart so the substance

expands, but the particles stay the same size.

Heat Expansion in Structures

Heat expansion is a factor that must beallowed for when designing and buildingroads, railways, bridges and buildings.

On a hot day metal and concrete willexpand, and will shrink again during a coldnight. If this was not allowed for, thestructure could warp or crack, and bedamaged.

These structuresare built with gaps,or flexible joints, toallow heatexpansion to occurwithout damage.

The Sydney Harbour Bridge has a hugehinge at the base of the steel arch so thewhole structure can flex and move.


11

Heat Expansion in a Gas Gas Pressure

Changes in Gas Pressure due to Heating

You might also investigate heat expansionin a gas, as suggested by these diagrams.

Expansion of a gas can be explained thesame as before... particles move fasterand push each other further apart.

However, what if the gas is inside a strongcontainer that cannot expand the way aballoon can?

Now you must know about Pressure.



Remember that in agas the particlesare constantlyflying everywhereat high speed.

They frequently collide with each other,and with the walls of their container.Each collision pushes on the inside ofthe container, or on each other. Thismeans there is a constant push, orforce, acting within the gas.

Pressure is measured as the amount offorce pushing per unit of area.

The unit of pressureused most often inscience is thekilopascal (kPa)

1 kPa = 1,000 N force per square metre.

Some examples of pressure valuesNormal air pressure (sea level) ≅ 100 kPa

Inflated car tyre ≅ 200 kPaInside a scuba airtank ≅ 800kPa

Flask full of air,with balloonfitted over it.

Air expands and inflates

balloon Air contracts and balloon

collapses

Heated in abowl of hot water

Cooled infridge

The “pascal” unit is namedin honour of the greatFrench scientist and

mathematician Blaise Pascal (1623-662).

What might happen if you heated a gas inside a strong container which cannot change its shape?

When heated, the particles move faster andpush harder against each other and thecontainer... so the pressure goes up.

OK, so it’s a strong container, but there is alimit to how strong it is. If the pressure risestoo high, the pressure can cause it to burst.

This why you should never dispose of an aeorsol spray can in afireplace or incinerator. As it gets hot the pressure will rise and it may explode.

Even more dangerous are pressure cylinders of fuel gas. If there is a fire in a house or factory,not only might the cylinder explode from rising pressure, but the escaping fuel will then burn.This is why large gas cylinders are always stored outside buildings.

Gas in a rigid container,before heating.

PressureGauge

measures gaspressure

After heating, particles move faster,

pressure rises




12

When heat is added to any substance, theparticles move a)....................................When the substance is cooled, theparticles move b)...................................

“Temperature” is really a measure of theaverage c).................................. of theparticles.

The melting of a solid occurs when heatcauses the particles to d)............. fastenough to e).......................................... theforces holding them in place. They thenbegin to move around, so the substance isnow a f)............................

In a liquid, adding heat causes the particlesto move around g)....................... Some mayhave enough energy to fly off as particlesof h).........................

Write the letter (A,B,C, etc) of the listitem which matches each description.Not all the list items will be used, andsome may be used more than once.

Description matches with List Item1. When a substance gets bigger .............due to being heated.2.What happens to the actual .............particles when they are heated.3.Why liquid rises in a .............thermometer.4.What is inside the bubbles when .............a liquid is boiling.5.Why leave a gap in a rail track? .............

At the “boiling point”, so many particlesform vapour that i)...................... of gas formwithin the liquid. We say that the liquid is“j)...............................”

Heat also causes most substances tok)................................... because the fastermoving particles push each other apartwhen they l)........................... with eachother.

If a gas is inside a container that cannotexpand, then heating will cause them).............................. to rise. Pressure iscaused by particles exerting a n).................when they collide. Pressure is the amountof o)............................. pushing per unit ofp)............................ The unit of pressureoften used in Science is the q).....................

Worksheet 3Particles & Heat. Expansion & Pressure


Worksheet 4Particles & Heat. Expansion & Pressure

Match the Lists

Student Name.............................................

Student Name.............................................

Description matches with List Item6.Pressure is “force per unit of..”? .............7.Temperature at which bubbles .............of vapour form inside a liquid.8. Measurement of the average .............speed of particles in a substance.

List ItemsA. areaB. volumeC. contractionD. melting pointE. heat expansionF. boiling pointG. temperatureH. move fasterI. vapour (gas)


13

Air Pressure

Tricks with Air Pressure

Air Pressure and Your BodyNormal air pressure at sea level is about 100 kPa. Over the area of your whole bodythis means a total force equivalent to about 1 tonne is pressing on you.

How come you don’t feelsquashed?

Simply because your body has the same amount of pressureinside, pushing outwards.

If you go up in an aircraft, ordrive up a high mountain, the outside airpressure gets less. You will feel the pressuredifference in your ears, until it equalisesagain.

Astronauts in space or on the Moon (noair) need pressure suits not just tobreathe, but to protect them from thezero pressure around them. Their own“body pressure” pushing outwardswould cause fatal damage without thesuit.



Air Pressure and WeatherMost of our winds, storms and weatherpatterns are due to air pressure effects in theatmosphere.

In some places, a huge “bubble” of the air(maybe 1,000 km across) can warm up. This“bubble” expands so that the air particlesbecome further apart and the air pressurebecomes lower than the surrounding air.This is a “low pressure cell”.

Meanwhile, in another place the air is coolingand contracting. The air particles are forcedcloser together, so the pressure rises... a“high pressure cell”.

Both pressure systems begin to rotatebecause of the spin of the Earth, so circularwinds blow around each “cell”.

Low pressure cells often bring stormsand rain (and cyclones) while “highs”tend to bring fine, dry weather. Bothcreate the winds that blow around them,and from one to the other.

Air Pressure

Totally fill a glass with water. Slide a piece of

cardboard over it so there are no air bubbles inside.

Support the cardboard withyour hand while carefullyturning the glass upside-

down. Let go of thecardboard.

The water defies gravity andstays in the glass!

Explanation: the air pressureforce on the cardboard is

stronger than the downwardweight of the water.

(But let air bubbles in, andsee what happens!)

Shelled, hard-bboiledegg, will NOT fit into

this flask

Place a smallamount of water in

the flask

Now boil thewater in the

flask. The flaskfills with watervapour whichpushes some of the air out.

Lesspressure

inside

Air Pressure

Turn off the heat, andimmediately place the egg on

the neck of the flask.

As the gas inside cools, andsome water vapour condenses,

the inside pressure drops.

Outside air pressure now pushesthe egg into the flask.

Fascinating to watch!


14

Density

1 kg Lead 1 kg cottonwool

Which is heavier? 1 kg of lead or 1kg of cotton wool?



Well, of course, they are the same mass;1 kg each. However, the lead has all itsmass packed in a very small space or“volume”, while the cotton wool occupiesa large volume for the same mass.

The real difference here is “Density”.

Density means the amount of mass per unit of volume.

In the laboratory, we would normally measure mass

in grams (g).

Volume means the amount of spacesomething occupies. Small solid

objects would normally be measured in cubic centimetres (cm3).

Liquid volumes aremeasured in millilitres (mL).

These 2 different units ofvolume are actually the

same amount.1 cm3 = 1 mL

1 cm 11 ccmm

1 cm volume

1 cm33

How to Calculate Density

Once the mass and volume of anythingis measured, its density can becalculated as follows:

Density = Mass Volume

D = m V

If mass is in grams, and volume in cm3, then

density will be in grams per cm3 (g/cm3)

Other possible units includeg/mL and kg/m3

Example Calculations1.A piece of lead has a volume of 2.5 cm3

and a mass of 27.5 g. What is its density?Solution: D = m / V

= 27.5 / 2.5= 11.0

∴∴ density is 11.0 g/cm3

2.A pack of cotton wool has a mass of 20gand it occupies a volume of 500 cm3.What is its density?Solution: D = m / V

= 20 / 500= 0.04

∴∴ density is 0.04 g/cm3




15

For each question show full working.Write your answer rounded to 1 decimalplace. Every answer must have units.1.A block of wood has a mass of 82g anda volume of 105 cm3.What is its density?

D = m / V

= ................... / .........................

= .............................

∴∴ density is ......................... ................(answer) (units)

2.A gold nugget (worth about $8,000) has amass of 300g and a volume of 15.5 cm3.What is its density?

3.A bottle of motor oil is labelled “500 mL”.The oil in it has a mass of 400g.What is its density?

4.The density of a piece of steel = 8.0 g/cm3.If the piece has a mass of 32g, what is itsvolume?

5.Aluminium has a density of 2.7 cm3.What mass is contained in a volume of 10 cm3?

6.Polystyrene foam plastic has a densityof 0.2 g/cm3. What volume of it do youneed to have a mass of 1kg (1,000g)?

Worksheet 5Skills Exercise

Calculating Density(calculator needed)

Student Name.............................................




16

Part AThe volume of a rectangular prism orcube can be found by multiplying length x breadth x height. (V = L x B x H)

For each of the followinga) calculate the volume (in cm3)b) calculate the density

1.This cube of copper is 2.0 cmon each side.

Its mass is 72g.What is its volume, and its density?

a) V = LxBxH b) D = m / V

= ........x.........x.......... = ........../ .......

= ..................... = ...................

Vol is .............. .... density is ..................(answer, units) (answer,units)

2.This brick

measures 22.5cm x11.0cm x 7.5cm.

Its mass is 5 kg (5,000g).Find its volume and density.

3.This empty box is 50cm high, 30cm

wide and 75cm long.What is its volume?

What would be the mass ofa block of concrete exactlythe same size as the box?

(density of concrete = 3.5 g/cm3)

4.A 750g box of breakfast cerealmeasures 21 x 13 x 9 cm. Find its volume and density.

5.This a cube of brass.Its density is 6.5 g/cm3 andits mass is 175.5g. Find its volume. How long is eachside?

Worksheet 6Skills Exercise (2 pages)

Calculating Volume & Density(calculator needed)

Student Name.............................................




17

Part BAnother way to measure volume is tolower a solid into water in a measuringcylinder. The water level rises.

The change in the cylinder reading isequal to the volume of the solid.

1. A lump of metal withmass 198g was lowered into a measuring cylinder.The cylinder had 35 mLof water in it. The metalcaused the water level to rise to 68 mL.

a) What is the volume of the metal?

b) What is its density?

2.Another lump of the same metal (samedensity!) caused the cylinder reading togo from 42 mL up to 55 mL.a) Volume of the metal?

b) What is the mass of this lump?

3.Yet another lump of this same metal waslowered into a cylinder containing 30mLof water. The metal had a mass of 252g.

a) What is the volume of this lump?

b) What would be the final reading of themeasuring cylinder?

4.Find the density of this piece of solid rock. Its mass = 120g.

Questions for DiscussionSome Limitations of this Methoda) Would this method of measuringvolume work for an object which floats inwater?

b) Would this method work for a solid likea sugar cube which will dissolve in thewater?

Worksheet 6 (cont)

35mL

33mL

80mL

68mL


18

Density and the Moving-Particle ModelHow does the Moving-Particle Model of matter explain density differences?

Solids, Liquids & GasesRemember how the particles are arranged inthe different states of matter.

In solids the particlesare packed closetogether, and fixed inplace.

In liquids, theparticles are alsoclose together, butable to move around.

In gases, the particlesare far apart andmoving at high speed.

We could predict from the model that solidsand liquids should have similar densities.Both solids and liquids should be far denserthan a gas, assuming the particles are all thesame weight.

Sure enough, if the density of any puresubstance is measured the results are similarto the following.

Example Density (g/cm3)Solid ice 0.92 Liquid water 1.0Water vapour 0.0007

Note that the solid and liquid densities aresimilar, and both much higher than the gas.

Water is unusual because the solid is lessdense than the liquid.

In most substances the solid is slightly moredense because the particles just move a bitfurther apart in the liquid, as shown in thediagrams above.

The slightly weird behaviour of ice andwater will be explained later.



Comparing Different SolidsHow does our model explain the differentdensities of different substances?

Particles Have Different MassCompare the metal aluminium with the metallead: Density (g/cm3)

Aluminium 3 (approx)Lead 11 (approx)

Why such a difference?

Both types of particles pack together tightly.They are a bit different in size, but moreimportantly, each lead particle is muchheavier than each aluminium particle. Lead isdenser because its particles are heavier.

Particles Pack DifferentlyCompare aluminium with silicon:

Density (g/cm3)Aluminium 3 (approx)Silicon 2 (approx)

In this case the particles of these 2substances are almost exactly the same sizeand weight. So why are their densities different?

It’s because of the way their particles pack together.

The particles of silicon do not pack as tightlytogether as those of aluminium, so thedensity is lower.

The density of every substancedepends on the mass of its particles,

and how they pack together.

Aluminium Lead

Aluminium Silicon


19

Density and Heat Expansion

Water the Weirdo!

You’ve already learnt about heat expansion. What does that do to density?Generally, as a substance gets hotter its particles move faster.

They collide harder and more often, and push each other apart slightly

When heat expansion happens, the substance (solid or liquid) gets bigger and has slightly more volume.Since D = m/V, if the volume increases,

but mass is still the same, then density must get less.

(However, these changes in density are only slight compared to the huge difference from liquid to gas.)



Adding heat makes the particles vibrate faster. As they jiggle andpush against each other, they are forced a little further apart.

This makes the solid substance get bigger and occupy more space.

Heat Added More Heat

SubstanceMelts

Particles in a liquid are still closetogether, but usually a bit further

apart than in the solid.

Most of the time, water acts just like allother substances.

For example here are its density valuesover a range of cooling temperatures.

Temperature (oC) Density (g/cm3)99 0.9675 0.9850 0.9925 0.997

5 1.00Like other substances, as you cool waterdown it shrinks slightly and its density rises alittle.

However, when you cool other substancesfurther until they freeze (solidify) they keepshrinking and density continues to rise. Butlook at what happens to water:

Temperature (oC) Density (g/cm3)5 1.000 (still liquid) 0.990 (ice) 0.92

As water freezes, it expands, and the density gets lower!

Why?

Why Water Expands on FreezingThis is tricky to explain. You need to knowthat the “particles” in water are not actuallyball-like, but shaped like this:

In liquid water,these particles can

wriggle in veryclose to each other

for maximumdensity.

However, as waterfreezes to ice theparticles are forcedto line up inorganized “ranks”,so they are actuallyslightly further apart.

This is whywater expands as it freezes, and

(that’s why a can of drink will split open if frozen)ice floats in water

(it has a lower density)


20

Density and FlotationWhy do some things float and others sink?

DiffusionYou might do one of these activities yourself, or see it demonstrated.

It’s all a matter of density. Study these diagrams to spot the rule.

Can you see the pattern? Things will float if their density is less than the liquid.They will sink if their density is more than the liquid.



Waterd = 1.0 gg//ccmm3

Wood d = 0.9 gg//ccmm3

Floats!

Steel d = 8 gg//ccmm3

Sinks!

Petrol d = 0.7 gg//ccmm3Wood

d = 0.9 gg//ccmm3


Both sink!

Mercuryd = 13 gg//ccmm3

Wood d = 0.9 gg//ccmm3


Both float!

How Can a Steel Ship Float?Because of its shape, the ship containsa lot of air within its total volume. Thismeans its overall density is only about0.7 g/cm3.

Since fresh waterhas d = 1.0 g/cm3, the ship floats.

It floats even better insea water which has a higher density. (salt water, d = 1.3 g/cm3)

If the ship gets a hole in it and enoughair spaces fill with water, the densityrises and it may sink.

A submarine hasspecial ballast tanks. When thesetanks are filled with air, the sub’s density isless than water, so it floats.

If the tanks are filled with waterthe sub’s density ishigher than water, so it candive.

Cruising underwater, the tanks are adjustedso that the sub has the same density as thesea... “neutral buoyancy”. In this state itneither sinks nor floats, but hangs in thewater, and it can manoeuvre easily.

Fluids (liquids and gases) seem to be ableto mix themselves together automatically.

This process is called “Diffusion”.

The coloured solution can mix itselfthrough the beaker of water. The browngas can mix with the air without any help.

The explanation is in the Moving-ParticleModel of matter. In liquids and gases, theparticles are moving around. If 2 differentgases or liquids are side-by-side, then themoving particles will automatically mix.

Is diffusion faster in liquid or gas?What effect would temperature have?

The food colourspreads out throughthe water by itself.

Without any stirring,it auto-mmixes

through the water.

oonnee ddrroopp ooffffoooodd ccoolloouurr

ddyyee

Water

Gas Jarof air

glassseparator

When theseparator is

removed, thetwo gases mix

themselvestogether.Gas Jar

ofbrown

gas




21

In both a)......................... and .....................the particles are very close together,compared to particles in a b).......................This means that the density of solids andliquids is much c)..............................(higher/lower) than a gas.

For most pure substances the density ofthe solid is slightly d)..................................(higher/lower) than the liquid because asthe substance melts, the particles get a bite)................................................. (furtherapart/closer together).

Different substances have differentdensities because their particles may havedifferent f)...................... , or because theirparticles may g)........................................... ina different way.

When heat expansion occurs in a solid orliquid, the substance gets bigger so itoccupies a larger h).............................. Thismeans its density i).................................(increases/decreases)

Water is an unusual substance because itj)............................. as it freezes. The result isthat ice is k)......................... (more/less) densethan water, so ice will l)........................... inwater.

Whether something floats or sinks dependson density. If an object is more dense than theliquid, it will m)....................... If it is less densethan the liquid it will n)......................

A ship is built from high-density steel floatsbecause its overall density is o)................. thanwater due to its shape and the manyp)................. spaces it contains. By adjustingthe amount of water or air in its“q)............................ tanks”, a submarine candive, surface, or “hang” in the water with“r)........................... buoyancy”.

Diffusion is when s)....................... or....................... can mix themselves together. Ithappens because the particles aret).................................. so they automaticallymingle with each other.

Worksheet 7Density & The Particle Model


Worksheet 8Sink or Float?

Student Name.............................................

Student Name.............................................

Here are the densities of 3 differentliquids, and 4 different solids. (all in g/cm3)

Liquids Solidswater 1.0 lead 11mercury 13.5 plastic 0.75olive oil 0.8 uranium 19

wood 0.9

The 3 liquids were poured into a containertogether. They did NOT mix, but formedlayers as shown in the diagram.

a) label the layers to show where eachliquid ended up.

Next, smallcubes ofthe 4 solidsweredropped in.

b) Sketchon thediagram toshowwhere eachone endedup.(label them)




22

1. (10 marks)Match each description to an item fromthe list. To answer, write the letter(A,B,C, etc) of the list item beside thedescription.

Description matches with List Item

i) The lowest density state of matter. .............

ii) Easily compressed fluid. .............

iii) Change of state from gasto liquid. .............

iv) Change of state from liquidto solid. .............

v) The state in which particles are held in one place. .............

vi) Energy which causes particlesto move faster. .............

vii) Force per unit of area. .............

viii) Mass per unit of volume. .............

ix) Process of fluids mixingthemselves together. .............

x) Incompressible fluid. .............

List Items Not all will be used. Some may beused more than once.

A. solid G. condensationB. liquid H. pressureC. gas I. freezingD. evaporation J. heatE. diffusionF. density

Score = ................. / 40

2. (6 marks)In the boxes below, use simple sketches torepresent a model of the particles in solids,liquids and gases.

In each sketch you must make it clear:• if particles are close, or far apart.• if particles are able to move around

Solid

Liquid

Gas

3. (6 marks)Briefly explain:a) what happens to the particles in a solidwhen the substance melts to become liquid.

b) why a substance expands when heated.

c) why the gas pressure increases in a sealedcontainer when it is heated.

Student Name.............................................Topic Test Solids, Liquids & Gases

Answer all questionsin the spaces provided




23

4. (4 marks)a) This is a glass of waterwith a piece of cardboardon top, which has been turned upside-down.

Explain why the waterdoes not fall out of the glass.

b) When the temperature increases,the liquid in this thermomter rises upinside the glass tube.

Explain why the liquid rises.

5. (6 marks)For each of the following, calculate thedensity of the object shown or described.

Marks will be awarded for showing your working.

a) mass = 240 g

b) A lump of metal with mass 150g wasdropped into a measuring cylinder of water.The water level rose from 40 mL to 55 mL.

6. (3 marks)Carbon exists in several different forms.Diamond has a density = 3.5 g/cm3.Graphite has a density = 2.3 g/cm3.Both forms are made up of exactly the sameparticles (same atoms).

a) Suggest a reason why they might havedifferent densities.

b) If you heated a diamond up, what wouldyou expect to happen to its density as it gothotter?

7. (5 marks)Fill in the blank spaces.

An object will float in a liquid if the object’sdensity is a)........................................... thedensity of the liquid.

If you cool a liquid until it turns solid, usuallyits density will b)................................... as itsolidifies. Water is unusual because ice isc).............................. dense than liquid water.This is because, as it freezes, the particles inwater re-arrange so they ared)............................................, and the volume ofthe water e)................................ as it freezes.

4 cm110 ccmm3

cm




24

Worksheet 1a) solid, liquid & gasb) shape c) cannotd) container e) flowf) compressed g) fillh) compressed i) meltingj) freezing k) evaporationl) condensation m) liquidn) sublimation o) Particlep) close together q) placer) vibrate s) close togethert) move around u) far apartv) moving

Worksheet 21.a) Particles are far apart, with a lot ofempty space between them.b) Particles are flying at high speed inevery direction.

2.Liquids and gases

3.a) Particles are very close together andcannot easily be pushed any closer.b) Particles are fixed in place and heldby forces of attraction.

4.a) Particles are not fixed in place andcan move around.b) Particles are very close together andcannot easily be pushed any closer.

5.Solids and liquids

6.a) Condensationb) Freezingc) Evaporation

Worksheet 3a) faster b) slowerc) speed d) vibratee) overcome (break free of)f) liquid g) fasterh) gas i) bubblesj) boiling k) expandl) collide m) pressuren) force o) forcep) area q) kilopascal (kPa)

Worksheet 41. E 5. E2. H 6. A3. E 7. F4. I 8. G

Worksheet 51.D = m / V

= 82 / 105 = 0.7809...

density is 0.8 g/cm3.

3.D = m / V

= 400 / 500 = 0.8

density is 0.8 g/mL.4.D = m / V8.0 = 32 / Vso V = 32 / 8

= 4.0volume is 4.0 cm3.5.D = m / V2.7 = m / 10so m = 2.7 x 10

= 27.0mass is 37.0 g.6.D = m / V0.2 = 1,000 / Vso V = 1,000 / 0.2

= 5,000volume is 5,000 cm3.

Answer Section

2.D = m / V

= 300 / 15.5 = 19.354...

density is 19.4 g/cm3.




25

Worksheet 6Part A1.a) V=LxBxH b) D = m / V

=2x2x2 =72 / 8= 8 = 9

Vol is 8.0 cm3. Density is 9.0 g/cm3.2.a) V=LxBxH b) D = m / V

=22.5x11.0x7.5 = 5,000/1856.25= 1856.25 = 2.693...

Vol is 1,856.3 cm3. Density is 2.7 g/cm3.3.a) V=LxBxH b) D = m / V

=50x30x75 3.5 = m / 112,500= 112,500 so m =3.5x112,500

Vol is 112,500 cm3. = 393,750Mass is 393,750 g

(about 394 kg)4.a) V=LxBxH b) D = m / V

=21x13x9 =750 / 2457= 2457 = 0.305...

Vol is 2,457 cm3. Density is 0.3 g/cm3.5.

D = m / V6.5 = 175.5 / V

So, V = 175.5 / 6.5= 27

Volume is 27 cm3

Since it is a cube, each side must be3cm (3x3x3 = 27)

Part B1.a) V = 68-35 = 33 mLb) D = m / V

= 198 / 33 = 6

density is 6.0 g/mL.2.a) V = 55-42 = 13 mLb) D = m / V

6 = m / 13So, m= 6x13

= 78Mass is 78.0 g

3.a) D = m / V

6 = 252 / VSo, V= 252/6

= 42Volume is 42 mL.b) Reading would rise to 72 mL. (30 +42)4.a) V = 80-33 = 47 mLb) D = m / V

= 120 / 47= 2.553...

density is 2.6 g/mL.

Questionsa) No, because if it is floating it hasn’t“pushed aside” its own full volume of water. Itmust be completely under to do so.b) No, it will not “push aside” the water.Its particles will mingle in with the waterand not displace it.

Worksheet 7a) solids & liquids b) gasc) higher d) highere) further apart f) masses (weight)g) pack together h) volumei) decreases j) expandsk) less l) floatm) sink n) floato) less p) airq) ballast r) neutrals) liquids or gases t) moving around

Worksheet 8

olive oil

water

mercury

plasic floatson oil.

wood floatson water.

lead floats onmercury.uranium sinksin mercury.




26

Topic Test1.i) C ii) C iii) G iv) I v) Avi) J vii) H viii) F ix) E x) B

2.Solidsclose togetherfixed in place

Liquidsclose togethermoving around

Gasfar apartflying everywhere

3.a) Particles begin vibrating more andmore until the forces cannot hold themin place. They start moving around.

b) Particles begin moving faster. Theycollide harder and push each other a bitfurther apart, so the substance getsbigger.

c) Particles move faster and collidemore often and with more force. Thisforce (per unit of area) is the pressure,so it goes up.

4.

a) the weight of the water is help up bythe air pressure pushing on thecardboard.

b) Liquid rises because of heatexpansion as the liquid gets hotter.

5. V = LxBxH

= 10x4x3V = 120 cm3.

D = m / V= 240 /120= 2

Density is 2.0 g/cm3.

b) Vol = 55-40 = 15 mL.D = m / V

= 150 / 15=10

Density is 10.0 g/mL.

6.a) The particles (atoms) pack togetherdifferently. (In diamond they pack closertogether)

b) Density will get lower. This is becauseheat expansion will make the volumeincrease, so density must decrease.

7.a) less thanb) increasec) lessd) further aparte) increases

Years 7-8 Solids, Liquids Gases

Documents

Transcript of Years 7-8 Solids, Liquids Gases