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Year 7-8 Topic 4 Separating Mixturescopyright 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.

Solute&

Solvent

Crystallisation

DistillationMagnetic AttractionEvaporation

Flotation&

Sedimentation

Filtration

Chromatography

Mixtures on Earth

Dilute,Concentrated,

Saturated

Separating Mixtures

Mixtures

SeparationTechniques

Importanceof Water as a

Solvent

Solutions&

Suspensions



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.

Solute&

Solvent

Crystallisation

Distillation

Magnetic Attraction

EvaporationFlotation

&Sedimentation

Filtration

Chromatography

Mixtures on Earth


Saturated

Separating Mixtures

Mixtures



SolventSolutions&

Suspensions

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.

Solute&

Solvent

Crystallisation

Distillation

Magnetic Attraction

EvaporationFlotation

&Sedimentation

Filtration

Chromatography

Mixtures on Earth


Saturated

Separating Mixtures

Mixtures



SolventSolutions&

Suspensions


5

What is a Mixture?To understand mixtures, you need to know about pure substances.

A substance is pure if it is made up entirely of particles that are identical to each other.

Scientists have goodreasons to believethat all substancesare made up of tinyparticles.

There are many different types of particles. The different types of particle are different fromeach other in their weight and density, in the way they cling together and in the way they

combine with other types. You will learn about atoms & molecules in a later topic.For now we will represent particles simply by different shapes and shadings.

A mixture is NOT PURE. A mixture is a substance made up of 2 or more different

types of particles mixed together, but not chemically combined.

Exactly what chemically combined means will beexplained in a later topic.



Three different pure substances

Scientific ModelsWhen we usediagrams like thisto describesubstances, is thisdescriptionrealistic?

Well, yes, and no.

We have many good reasons to believe thatall matter is made up of small particles calledatoms. Often they join together in largerlumps called molecules.

However, we also know that atoms are notsolid ball-like particles, but are made up ofmany smaller pieces.

Overall, the description above is partly true,but is simplified, and 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 simplified or notquite the full story.

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

Simplified model of DNA, the most complex molecule known

Mixture




6

Mixtures Around UsWe are surrounded by mixtures... we breathemixtures, eat them, drink them and swim inthem. We wear them and make art usingthem.

Nearly everything around us is a mixture.

The Solid Earth

Soil is a complex mixture of minerals, waterand the remains of dead plant materials.

The OceansThe oceans cover2/3 of the Earth toan average depth ofseveral kilometres.The oceans aremixtures of (mainly)water and salt.

The AtmosphereThe Earth is surrounded by a layer of air...theatmosphere.

Air is a mixtureof gases, oftenwith clouds oftiny waterdroplets driftingabout.

ooxxyggeenn

carbondioxidecondensed

watervapour

nitrogen

The Earth ismostly madeof rock, witha thin layerof soil on

top. Rocksare mixtures

of variousmineralscombinedtogether.

We Use the Earths ResourcesResourcesA Resource is any substance which weneed and use.

Natural ResourcesThese are things we need and use whichoccur naturally on Earth.

Many resources come from living things. Forexample, cottonand woolare fibres which weuse to make clothing, carpets andfurnishings. Cotton is a plant fibre. Wool, ofcourse, is the hair or fur of a sheep.

Other things are non-living resources.For example, water is one of our most basicand necessary resources. The water we needfor drinking, washing, irrigation and industryis collected from lakes and rivers.

Sand is a simple resource used to makecement, concrete and glass. We simplygather it from the Earth.

Made ResourcesThese are useful substances which do notoccur naturally, but are made artificially.

To make these things, we start with somenatural resource, but treat it and modify it soit becomes a totally new substance.

For example, plastics are a range ofsubstances used to make furniture, car parts,toys, pipes, kitchen utensils, etc, etc.Plastics do not occur naturally. They aremade by chemical processing of substancesextracted from petroleum.

Dyes and pigments are used to add colour tofabrics, plastics, paint, ink, etc. Althoughsome dyes can be extracted from naturalplant and animal sources, most modernpigments are made artificially from chemicalsextracted from coal or petroleum.




7

Solutions & SuspensionsIf you mix a solid substance with a liquid, oneof 2 things is likely to happen... either itdissolves in the liquid, or it does not.

Salt Dissolves in WaterIf you add solid salt to water and stir to mixthem together, the salt seems to disappear.

This mixture is a solution.The salt particles and the water particles aremixed together so intimately that the saltcannot be seen. If you let it stand, the salt willnever settle to the bottom.

Solutions and the Particle Model

Particles Particlesin a solid in a liquid

If the solid is soluble in this liquid it willdissolve to form a solution.

The lump of solid materialcompletely comes apart and itsparticles are mixed evenlyamong the particles of liquid.

The different particles cling to each other sothe particles of solid cannot fall to thebottom, but stay spread throughout themixture.

When stirred,the salt

dissolves Clearsolution

Chalk Dust wont DissolveIf you mix some chalk dust (or similar solid)with water, no matter how much you stir, itwill not dissolve.

This is a suspension.

The solid is not dissolved in the liquid. You can see thecloudiness of it. If you let itstand, the solid will graduallysettle to the bottom.

Suspensions and the Particle Model

Particles Particlesin a solid in a liquid

If this solid is insolublein this liquid it will not dissolve, but may mixto form a suspension.

The solid particles are still in clumps. Theymay be too small to see, but they are notevenly spread in the liquid.

The clumps willeventually settle to thebottom.

When stirred,the chalk willNOT dissolve cloudy, whitesuspension

clear liquid.

ssoolliidd sseeddiimmeenntt

You should learn to recognise solutions and suspensions. Solutions may be coloured, but are always clear and see-through.

The solid will never settle out from a solution. Suspensions look cloudy and block the light. Suspended solids will eventually settle out.




8

Solute, Solvent, SolutionMore to learn about solution mixtures:

Particles in a solid

The substance whichdissolves is called the Solute.

Particles in a liquid

The liquid it dissolves into is called the

Solvent.

This mixture of solutedissolved in solvent, iscalled a Solution.

Dilute & ConcentratedIf there is only a verysmall amount of solute dissolved, we say that the solution is Dilute.

Example: 1 grainof salt dissolvedin a glass of water.

If there is a large amount of solute dissolved, we say that the solution is Concentrated.

Example: 3 spoonsof salt dissolvedin a glass of water.

SolubilityWhen a substance (solute) will dissolve in aliquid, we say it is soluble in that liquid. If itwill not dissolve, we say it is insoluble.

Each solute may have a different solubility indifferent solvents.

For example, salt is soluble in water, but isinsoluble in petrol.

Oil will not dissolve in water, but iscompletely soluble in petrol.

Sugar will dissolve in water, and will alsodissolve in petrol: it is soluble in bothsolvents, although not equally in each.

Saturated SolutionThere is usually a limit to how much solutewill dissolve in a given amount of solvent.When this limit is reached, and no moresolute can be dissolved, the solution is saidto be Saturated.

The Effect of TemperatureGenerally, the amount of solute that willdissolve increases with temperature.

For example, you can dissolve a lot moresugar in hot water than you can in cold water.This is true for most solutes that are solublein water.

Strangely enough, the solubility of salt doesnot change very much from cold to hot water.

Solubility of GasesGases such as oxygen from the air can besolutes too, but the amount that will dissolveis often very small.

It is this small amount of dissolved oxygenthat fish, and other water-living creatures,rely on for breathing in water.

However, the temperature effect on solubilityis the opposite of what happens with mostsolids... as the temperature goes up, theamount of gas that will dissolve goes down.As water gets warmer, the fish begin tosuffocate!




9

A pure substance is something that isentirely made up of a)................................that are b)............................ to each other.

Any substance that is not pure, must be ac)............................

We are surrounded by mixtures. The air isa mixture of d)............................. Theoceans are a mixture of (mainly) e)..............and ......................... The solid Earth ismostly rock, which is a mixture of differentf)................................

g)....................... resources are substanceswe need and use, which occur naturally.Some come from living things, (exampleh)........................) others are non-living.(example i)........................)

The opposite of a natural resource is aj)..................... resource.

Match the ListsFor each definition, write the letter (A,B,C, etc)of the matching List Item.

Definitions matches with1. Substance made of

identical particles .............2. rocks are mixtures

of these. .............3. A natural, non-living

resource. .............4. Substance containing

different particles. .............5. A mixture of gases

surrounding us. .............

List Items (not all will be used)A. waterB. atmosphereC. pure

Worksheet 1Mixtures

Fill in the blank spacesStudent Name.............................................

Worksheet 2Solutions & Suspensions.Supply the missing word

for each definition.

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

D. plasticE. mixtureF. minerals

1. A mixture where a solid is dissolved in a liquid. .........................

2. Name for the solid whichis dissolved. .........................

3. A solution which has only a small amount of solid. .........................

4. A mixture of solid & liquidwhich will separate if allowedto stand. .........................

5. Description of a solid which will not dissolve in a liquid. ....................

6. The liquid part of asolution. .........................

7. A solution with a large amount of solute. .........................

8. Description of a solidwhich will dissolve. .........................

9. A solution with the maximumamount of dissolved solid........................

10. What an increase in temperatureusually does to solubility.........................




10

The Importance of Water as a SolventInside Living ThingsAll living things are mostly made of water.Your body is made of microscopic bagscalled cells, which are filled with a watersolution.

You will learn more about cells in othertopics. For now, just note that water is thesolvent of life. Many of the chemicals whichmake up living cells are dissolved in water.

Your blood is mostly made of water. Itcirculates around your body carrying vitalchemicals to your brain and other bodyorgans. Many of these chemicals, such asfood nutrients, are carried dissolved in yourblood.

In the EnvironmentWater is also important as a solvent in theenvironment of living things.

Plants need many minerals so they can growand be healthy. They get these minerals fromthe soil by absorbing them through theirroots. The minerals must be dissolved in thewater in the soil, so the plants can absorbthem.

Most of the aquatic plants and animals(aquatic = living in water) have to breatheoxygen, just as we do. The difference is thatthey breathe the oxygen that is dissolved inwater.

Water is the vital solvent of life.

GENERALISED DIAGRAM OF A LIVING CELL

MMeemmbbrraannee oonn tthheeoouuttssiiddee ccoonnttaaiinnss tthheecceellll ,, aanndd ccoonnttrroollss

wwhhaatt ggooeess iinn oorr oouuttCytoplasm

iiss aa wwaatteerr ssoolluuttiioonnwwhhiicchh ffiillllss tthhee cceellll

Structureswithin the

cell

Water is the Solvent in the OceansMost of the water on Earth is in the oceansand has salt and many other mineralsdissolved in it.

All the salt has been dissolved out of therocks and soil by rainwater seeping throughover many millions of years. This has notonly created the salty oceans, but isimportant in the weathering of rocks and soilformation on land.

Human Uses of Solvent WaterWater is important as a solvent in manysituations in everyday life, in the workplace,and in industries. Water is the solvent inmany medicines, in tea, coffee and milk.

When you wash your hands, or have ashower, or wash the dishes, or do the laundryyou are relying on water to dissolve the dirtand wash it away.

To help it clean better, you use soap ordetergents which break up insoluble greasydirt so it is carried away suspended in thewater.

In many industrial processes, water is usedas a solvent so that important chemicals canbe easily pumped through pipes, or mixedwith each other.

Whether you drink it, wash with it or swim init, water is the number one solvent and

natural resource for our society and for allliving things.


11

Separating MixturesThe rest of this topic is all about how you can separate the parts of a mixture.

As well as learning more about the properties of matter, you will be learning about techniques and methods which are commonly

used in scientific laboratories, and in many industrial processes.

If you had a mixture of dry sand andpebbles, how would you separate the sandfrom the stones?

You could possibly pick out all the stonesone-by-one with your fingers, but a quickand easy way is to use a sieve.

The sand grains fall through the wiremesh, while the stones cannot fit throughand are caught on top of the mesh.

Can you see which property of sand andpebbles allows this separation to work?

It is simply the different grain size.



Sieves are commonly used in manyindustries to separate substances withdifferent grain sizes.

In a flour mill, wheat grains are cracked openby heavy rollers to release the powdery flourinside. Then the husk of the wheat seedsneeds to be removed. This is done bysieving. Flour falls through a fine mesh sieve,but the seed husks are too big and aretrapped on the mesh.

Gravel is used in making concrete, or forroad-building. It is important that all thestones are about the same size.

Gravel and crushed rocks are passedthrough sieves of different mesh sizes tocollect coarse or fine gravels separately.

The Importance of PropertiesEvery pure substance has a unique set ofcharacteristics, or properties.

These properties include colour, density,solubility, particle size, melting point,boiling point, and many more.

Differences of PropertiesAllows Separation

To separate any mixture into its parts, orfractions, you take advantage of thefact that each part of the mixture hasdifferent properties.

As you learn about each method, look outfor how a particular difference in propertiesallows the fractions to be separated.

Separating Solid Mixtures by Sieving

Crushing and sievingequipment at a rock quarry


12

Flotation & Sedimentation

Centrifuging Copper Refining

An Idea for a Neat ExperimentImagine you had a mixture of dry sand andsawdust, and wanted to separate them.

Sieving might work, but a lot of the sawdustgrains may be the same size as sand grains,and will sneak through the sieve with thesand.

Try this! Drop the mixture into a beaker of water, stir it, then let it stand.

The sawdust floats.The sand sinks.

Scoop the sawdust off the top and dry it.Carefully pour off the water, collect the sandand dry it. Mission accomplished!

Difference in Properties?Firstly, neither the sand nor the sawdustdissolve in water, so they form a suspension.The separation then occurs because ofdifferences in density.



SedimentationWhenever a solid-liquid mixture is asuspension, it will separate if you just leave italone.

If the solid settles to the bottom to form asediment, the process is calledsedimentation, if it floats it is flotation.

Note that this will NOT work for dissolvedsolids in a solution. The solid particles in asolution are intimately mixed in with thesolvent particles and they cling to each otherso that the solid will never separate.

Sedimentation is the process by which mudand sand settle to the bottom of lakes andseas. (More on that in a later topic!)

Sedimentation is important in seweragetreatment. After primary treatment, the solidsludge is allowed to settle to the bottom ofa sedimentation pond. The clear water canthen be released into the environment, ortreated further and re-cycled.

A Centrifuge is a machine which speeds upsedimentation by spinning a mixture aroundat high speed.

The spinningaction causessediments tosettle faster.

The spin cycleof a washing

machine has acentrifuge effect.

Water is separated from the clothes muchfaster compared to simply letting it drip out.

Centrifuges are used to separate cream frommilk in a dairy factory, and are widely used forseparations in scientific laboratories.

Copper is one of our most important metals.When copper ore is mined, the valuablecopper minerals are mixed with largeamounts of useless rock.

To separate the copper minerals, the ore iscrushed to a powder, then mixed with waterin huge vats.

A special oil is added and compressed air isbubbled through the mixture.

The useless rock particles settle to thebottom (sedimentation), but the copperminerals cling to the oil and form a froth ontop. This can be skimmed off to collect thecopper minerals and re-cycle the oil.

This is called Froth Flotation

Water


13

FiltrationFiltration can be used to separate a suspension mixture.

It WILL NOT separate the parts of a solution.

EvaporationEvaporation can be used to collect the solid from a solution.

For some suspensions, like sand inwater, the solid will rapidly settle to thebottom and form a sediment.

Suspensions containing very fine solidsmay take days to settle. In this case itmay be better to filter the mixture.



If you try to filter a solution, you will quicklyfind out that you cannot separate its parts thatway. Why not?

Simply because in a solution, the particles ofdissolved solid are about the same size asthe particles of liquid. Since the liquid canflow through the filter paper, so can thedissolved solid.

To collect the solid,the best way is to

evaporate the liquidsolvent. You can just

leave it in an opencontainer to slowlyevaporate at room

temperature, or heatthe solution to

speed the process up.

Why does it work?

The solute and thesolvent have a bigdifference in their

boiling points.

Water slowlyevaporates at room

temperature, andwill boil and

vapourise at 100oC.

Most dissolvedsolids will not

evaporate unlessheated to

much highertemperatures.

What property difference allows separation?

Grain size!

Although the grains of the suspended solidmay seem very small, they are very muchlarger than the particles of the liquid.

The filter paper has microscopic channelsand holes between its fibres, and the particlesof liquid can easily flow through. The solidgrains are much larger, and are caught in thefilter paper.

Filtration is really the same as sieving.at a different size scale.

The solid caught in the filter paper is called the residue.

The liquid which passes through is called the filtrate.

Suspension mixture

Filtration funneland

filter paper

Residue collected in filter paper.

Clear filtrate passes through.

Crystals of copper sulfatecollected from a solution

by evaporation

Evaporatingbasin

The waterevaporates away and leaves thesolid behind.


14

DistillationDistillation can be used to collect the liquid from a solution

An Experiment You Might Do

Flaskcontaining solution

to be separated.

The solution boils,and the solventevaporates.

As the vapourpasses through thecondenser, it iscooled so that itcondenses back toliquid.

The solute remainsin the flask.



What difference in properties allows this to work?The solvent and the solute have very different boiling points.

The solvent boils and evaporates. Then the vapours are condensed back to liquid.The solute remains behind in the flask.

This hose bringscooling water

from a tap

Condenser

The condenser is atube within a tube.

Cold water flowsthrough the outer

tube and cools thehot vapour flowingin the central tube.

The vapourcondenses, and

pure, liquid solventflows out the end.

If you stir some copper sulfate into water itforms a blue coloured solution. Now stir insome chalk dust, or calcium carbonate. Thiswill not dissolve, but forms a suspension.

The mixture could be represented by this

diagram.

Water particle(solvent)

Dissolved coppersulfate particle

(solute)Particle of suspended solid

calcium carbonate

How could you separate this mixture tocollect some pure water, pure coppercarbonate and pure calcium carbonate?

Filter first, then evaporate & distil

FiltrationThe suspended solid(calcium carbonate) is

trapped in the filter paper

EvaporationCrystals of solidcopper sulfate

The filtrate is a solution ofcopper sulfate in water

divide in 2 parts

DistillationPure water

collected fromthe condenser


15

ChromatographyChromatography can be used to separate mixtures containing very small

quantities of quite similar chemicals, such as the dyes in ink.It is used mainly to find out what is in a mixture (analyse it)

rather than to separate the parts for collection.

CrystallisationCrystallisation (or re-crystallisation) is often used to remove

small amounts of impurities from a soluble substance.It is used mainly as a way to purify chemicals for scientific or medical uses.

Strip of filter papertaped to a glass rod

Small spot of texta ink(must be above the liquid)

Water, or other solvent

If this is left alone forsome time, the solventsoaks up through the filterpaper. As it rises abovethe spot of ink, it carries



some of the dyes with it. Soon you can seethat what seemed to be one colour of inkactually contains several different dyes.

You might experiment with different coloursof texta, or food colourings. Try differentsolvents, such as water with somemethylated spirit mixed into it.

You can hang the filter paper up to dry, andkeep your chromatograms.

How does it work?Texta ink may contain several different dyesmixed to give the visible colour.

As the solvent climbs up through the paper, itcarries the soluble dyes with it. However,different chemical dyes cling to the paperfibres. Some cling tighter than others, so thefurther the solvent travels, the more the dyesare separated from each other.

This diagram representsa crystal of a usefulchemical, but it has

some impurities mixedwith it.

Some of the impurities do not dissolve.These can be removed by filtration.

Next, the solution is allowed to cool, orthe solvent is allowed to evaporate.

To purify it, the first step is to dissolve itin a suitable solvent to make a veryconcentrated solution. This is oftenheated, for maximum solubility.

Solvent particlesUseful chemicalSoluble impurityInsoluble impurity

The dissolved chemical nowbegins to form solid crystalsbecause the solution cannothold so muchsolute.

These crystalsare very pure.

The soluble impurities mostly stay in solutionbecause they are not so concentrated and donot crystallise.

This is how chemicals for laboratories or formedicines can be made 99.999% pure.




16

Which method of separation would you use,if you want to collect...

1. some sugar from a sugar solution? .........................

2. rice grains, which have accidentally been mixed with flour? .........................

3. some pure water fromsalty water? .........................

4. some salt from salty water? .........................

5. some clear water frommuddy water? .........................

6. sawdust, which has been mixed with sand? .........................

7. copper oxide, from a suspension in water? .........................

8. pure water from a solution of copper sulfate. .........................

9. the steel buttons that are mixed in with plastic buttons? .........................

10. clear water from a mixture containing insoluble solids.......................

Worksheet 3Separating Mixtures

Choose the best method to achievethe separation described

Worksheet 4Methods of Separation

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

2. Fred is learning to cook, but hes better atScience than cookery. Hes accidentallymixed the icing sugar with the corn flour andspilled some rice into it as well. (Icing sugar and cornflour are both fine powders. Icing sugaris soluble, corn flour is not.)To separate this mess, he firstly sieved it.What went through the sieve he stirred intowater, and let it stand overnight. In themorning a sediment had formed. He carefullypoured the clear liquid into a tray and put itinto the warm oven to evaporate.

a) What was caught by the sieve? ....................................

b) What difference in properties allows substances to be separated by sieving?

....................................................................

c) What was the sediment? ........................d) What solid will be in the

oven tray when dry? .........................e) What other method might Fred have

used to collect the substance which was a sediment? ....................................

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

1.A student was given a mixture containingcopper oxide (insoluble) and copper sulfate(soluble) and asked to separate them. Firstly,she stirred the mixture into water, then filteredit. Next, she evaporated the filtrate.

a) What substance was the residue in the filtration?..........................

b) Describe what the filtrate was.

....................................................................c) What difference in properties allows

substances to be separated by filtration?

....................................................................d) What substance was

collected by evaporation?........................e) What difference in properties allowed

this separation?......................................f) The copper sulfate collected was found to

be impure. What process could be used to purify it? ..............................................




17

ExampleThe following diagram is a flowchart ofthe method used to separate the mixturedescribed in Worksheet 4, Question 1.

Study it to get the idea, then try to makeyour own flowcharts for the separationsdescribed.

Problem 2A mixture of pebbles, fine sand and salt was sieved.What passed through the sieve was mixed with waterand allowed to stand. A sediment formed. The clearliquid was poured off and evaporated. The sedimentwas also dried.

Use a flowchart to show the procedure and what was collected.

Problem 3A mixture of salt, water and chalk dust (insoluble)was filtered. The residue was dried. The filtrate wasdivided into 2 parts. One part was evaporated, theother part was distilled.

Construct a flowchart and show what was collected at each step.

Skills Worksheet 5Flowcharts of Separations Student Name.............................................

Evaporation copper sulfate

Stir into water

Residuecopper oxide

Filtrate

Filter

Mixture of copper oxideand copper sulfate

Problem 1Dirty, salty water was filtered. The filtrate wasthen distilled.

Use a flowchart to show what was collected at each step.




18

Separating Mixtures to Obtain ResourcesMost of the substances around us (land, sea, air and living things) are mixtures.

To obtain the many resources we need, we often have to separate the things we want from the mixtures in which they occur.

The following are just a few examples.

EvaporationSalt is separated from sea water byevaporation.

Sea water is pumped into wide, shallowponds. Over a period of weeks, the heatof the Sun evaporates the water leavingsolid salt behind.

If necessary, the salt can be purified bycrystallisation.

Sieving(already mentioned)

Sieves are used to separate flour from thewheat husks in a flour mill.

Sieves are used to separate different sizesof gravel for making concrete and forroad-building.

Gravel is a very simple natural resource,and we use millions of tonnes of it.

DistillationDistillation is used in the production of ethanol,which is now being added to petrol to makesupplies last longer.

To make ethanol, corn starch or cane sugar isfirst fermented. This process is basically thesame as the making of beer or wine.

The fermented brew contains 15% ethanol.Distillation is used to separate almost pure

ethanol from the water mixture. Sedimentation & Filtration

These separation methods are often involvedin collecting our most important natural

resource... water!

In many places, the water supply comes from ariver, lake, or from underground. Often thewater is dirty and is not safe for drinking.

Water is usually pumped into a large reservoirwhere it stays long enough for some of thedirt to settle to the bottom as a sediment.

The water may then be pumped through hugefilters to trap any remaining suspended solids,

so it is clear and clean for human uses.

Magnetic SeparationYou know that iron and steel areattracted to magnets, while other

substances are not.

This difference in properties is usedin the re-cycling industry to separatethe ferrous metals from other re-cycled metals such as aluminium.

Scrap metal, about to beseparated by an

electromagnet




19

Topic Test - MixturesAnswer all questionsin the spaces provided.

1. (8 marks)For each pair of items, state clearly whatis the difference between them.

a) A mixture and a pure substance

b) A solution and a suspension

c) A solvent and a solute

d) a dilute solution and a concentratedsolution

2. (8 marks)True or False? (T or F?)a) For most substances, solubility

increases at higher temperature. ........b) Filtration will separate a

suspension mixture. ........c) Sieving works because of a

difference of solubility. ........d) Evaporation collects the solvent

from a solution. ........e) The solid in a solution will form a

sediment. ........f) Distillation is involved in making

ethanol for use as a fuel. ........g) Crystallisation can separate the

different dyes in some ink. ........h) Oxygen gas is more soluble in

hot water than cold water. ........

3. (5 marks)What substance would be collected if:

a) you kept the filtrate after filtering asuspension of sand in water?

b) salt water is distilled?

c) an impure sample of copper sulfate wasdissolved in hot water and re-crystallised?

d) pure water was evaporated?

e) you dry the residue after filtering dirtywater?

4. (5 marks)A mixture of sand, salt and sawdust wasstirred into water and the mixture wasallowed to stand.a) How might you collect pure sawdust?

b) What is the sediment which forms?

c) The clear liquid was poured off and dividedinto 2 parts. One part was evaporated, and theother was distilled.i) What substance would be collected bydistillation?

ii) What would be collected from theevaporation?

iii) What difference in properties allows theseparation in both evaporation anddistillation?

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

Score / 26




20

Answer Section

Worksheet 1a) particles b) identicalc) mixture d) gasese) water and salt f) mineralsg) Natural h) wool, cottoni) water, sand j) made

Match the Lists1. C 2. F 3. A 4. E 5. B

Worksheet 21. solution 6. solvent2. solute 7. concentrated3. dilute 8. soluble4. suspension 9. saturated5. insoluble 10. increases it

Worksheet 31. evaporation 6. flotation in water2. sieving 7. filtration3. distillation 8. distillation4. evaporation 9. magnetic attraction5. filtration 10. filtration

Worksheet 41.a) copper oxideb) A solution of copper sulfatec) Particle sized) Solid copper sulfatee) Boiling pointsf) Crystallisation

2.a) Riceb) Particle sizec) Corn flourd) Icing sugar (or just sugar)e) Filtration

Skills Worksheet 51.

2.

Distillation water

Residuedirt

Filtrate

Filter

Mixture dirty, salty water

Liquidevaporated

Sediment dried

sand

salt

Stir into water

Pebbles caught in sieve

Sieving

Mixture of pebbles, sand, & salt

Distillation

Filtrate

Evaporation

watersalt

Dried residue.Chalk

Filtration

Mixture of salt, water &chalk

3.




21

Topic Test Answers1.a) A pure substance is made up ofparticles which are all identical. Amixture contains different particles(which are not chemically combined).

b) In a solution the solute is dissolved,and will never separate bysedimentation. In a suspension thesolid is not dissolved and will form asediment (or float).

c) A solvent is the liquid part of asolution, while a solute is the dissolvedsubstance.

d) a dilute solution has a very smallamount of solute, while a concentratedsolution has a large amount of solute.

2.a) T e) Fb) T f) Tc) F g) Fd) F h) F

3.a) waterb) waterc) pure copper sulfated) nothinge) dirt

4. a) It floats, so scoop it off and dry itb) sandc) i) water

ii) saltiii) difference in boiling points

04.mixtures

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