Physical Nature of Matter

8/9/2019 Physical Nature of Matter

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1.1 Physical Nature of Matter 1.1.1 M !!"# $% M &" 'P () P#!$*+"%For a long time, two schools of thought prevailed regarding the nature of matter. Oneschool believed matter to be continuous like a block of wood, whereas, the otherthought that matter was made up of particles like sand. Let us perform an activity todecide about the nature of matter is it continuous or particulate?

Activity ______________ 1.1 ake a !"" mL beaker. Fill half the beaker with water and mark the level of water. #issolve some salt$ sugar with the help of a glass rod. Observe any change in water level. %hat do you think has happened to the salt? %here does it disappear? #oes the level of water change?

&n order to answer these 'uestions we need to use the idea that matter is made upof particles. %hat was there in the spoon, salt or sugar, has now spread throughoutwater. his is illustrated in Fig. !.!.

Fig. 1.1: When we dissolve salt in water, the particles of salt get into the spaces between particlesof water.
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Fig. 1.2: Estimating how small are the particles of matter. With every dilution, though thecolourbecomes light, it is still visible.

1.1., ( %M ++ #" ! "%" P #!$*+"% () M !!"# Activity ______________ 1.2

ake ()* crystals of potassium permanganate and dissolve them in !"" mL of water. ake out appro+imately !" mL of this solution and put it into " mL of clear water. ake out !" mL of this solution and put it into another " mL of clear water. -eep diluting the solution like this to / times. &s the water still coloured?


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Fig.1.5: a, b and c show the magni ed schematic pictures of the three states of matter. Themotion of the particles can be seen and compared in the three states of matter.

Activity _____________1.13 ake some camphor or ammonium chloride. 0rush it and put it in a china dish. 1ut an inverted funnel over the china dish. 1ut a cotton plug on the stem of the funnel, as shown in Fig. !.2.


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Fig. 1.7: Sublimation of ammonium chloride

3ow, heat slowly and observe.

%hat do you infer from the above activity?4 change of state directly from solid to gas without changing into li'uid state 5or viceversa6 is called sublimation.

M ATERIALS R EQUIREDAmmonium chloride (or camphor or naphthalene or iodine or any other sublimable solid), china dish,funnel, cotton plug, burner, tripod stand, and a wire gauge.

P ROCEDURE1. Take powdered sublimable solid in a china dish.2. Put an in erted funnel o er the china dish.!. "nsert a cotton plug on the stem of the funnel.


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#. Put china dish o er the wire gauge on the tripod stand.$. %eat the china dish slowly with the help of a burner.&. 'o er the outer surface of the funnel with wet cotton to sublime the apours uickly.

Fig. 6.1 : Sublimation of ammonium chloride

O BSERVATIONSA sublimable solid on heating directly get con erted into apours,that sublimes back on cooling directly into solid again on the walls of the funnel.

R ESULTS AND D ISCUSSIONA sublimable solid on heating directly con erts into gaseous state. %ow "sit because of the high apour pressure of the li uid state of the solid. Theli uid state is practically non*e+istant.

P RECAUTIONS %eat the sample carefully. Take care in plugging the stem of the funnel securely with cotton. The si-e of the mouth of the funnel and china dish should becomparable. o not remo e the funnel when hot.

N OTE FOR THE T EACHER /oth repellent balls are easily a ailable which can be crushed and can also be used as a sample inthis e+periment.


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(a) (b) (c)

Fig. 11.1 : Separation of components of a mixture of common salt. (a) Residue containing sand and common saltdissolved in water; (b) Separation of sand by filtration; and (c) Obtaining common salt by evaporation

IS M ATTER AROUND U S P URE7ow do we 8udge whether milk, ghee, butter, salt, spices, mineral water or 8uice thatwe buy from the market are pure?

Fig. 2.1: Some consumable items7ave you ever noticed the word 9pure: written on the packs of these consumables?For a common person pure means having no adulteration. ;ut, for a scientist allthese things are actually mi+tures of di


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,.1 hat is a Mi0ture=i+tures are constituted by more than one kind of pure form of matter, known as asubstance. 4 substance cannot be separated into other kinds of matter by anyphysical process. %e know that dissolved sodium chloride can be separated fromwater by the physical process of evaporation. 7owever, sodium chloride is itself a

substance and cannot be separated by physical process into its chemicalconstituents. >imilarly, sugar is a substance because it contains only one kind of pure matter and its composition is the same throughout. >oft drink and soil are notsingle substances. %hatever the source of a substance may be, it will always havethe same characteristic properties. herefore, we can say that a mi+ture containsmore than one substance.

,.1.1 ! P"% () M$2!'#"%#epending upon the nature of the components that form a mi+ture, we can havediome other e+amples of suchmi+tures areA 5i6 salt in water and 5ii6 sugar in water. 0ompare the colour of the solutions of the two groups. hough both the groups have obtained copper sulphate solution but theintensity of colour of the solutions is diuch mi+tures are called heterogeneous mi+tures. =i+tures ofsodium chloride and iron Blings, salt and sulphur, and oil and water are e+amples ofheterogeneous mi+tures.

Activity ______________ 2.2 Let us again divide the class into four groups 4, ;, 0 and #. #istribute the following samples to each groupA

Few crystals of copper sulphate to group 4.

One spatula full of copper sulphate to group ;. 0halk powder or wheat Cour to group 0. Few drops of milk or ink to group #.

Dach group should add the given sample in water and stir properly using a glass rod. 4rethe particles in the mi+ture visible?

#irect a beam of light from a torch through the beaker containing the mi+ture and observefrom the front. %as the path of the beam of light visible?

Leave the mi+tures undisturbed for a few minutes 5and set up the Bltration apparatus inthe meantime6. &s the mi+ture stable or do the particles begin to settle after some time?

Filter the mi+ture. &s there any residue on the Blter paper?#iscuss the results and form an opinion.

Groups A and have got a solution. Group ! has got a suspension. Group " has got a colloidal solution.


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Fig. 2.2: #iltration3ow, we shall learn about solutions, suspensions and colloidal solutions in thefollowing sections.

,., hat is a %olution4 solution is a homogeneous mi+ture of two or more substances. Eou come acrossvarious types of solutions in your daily life. Lemonade, soda water etc. are alle+amples of solutions. sually we think of a solution as a li'uid that contains either asolid, li'uid or a gas dissolved in it. ;ut, we can also have solid solutions 5alloys6 andgaseous solutions 5air6. &n a solution there is homogeneity at the particle level. Fore+ample, lemonade tastes the same throughout. his shows that particles of sugaror salt are evenly distributed in the solution.


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,.,.3 ! $% *(++($& + %(+'!$(N he mi+ture obtained by group # in activity (.( is called a colloid or a colloidal

solution. he particles of a colloid are uniformly spread throughout the solution. #ueto the relatively smaller siGe of particles, as compared to that of a suspension, themi+ture appears to be homogeneous. ;ut actually, a colloidal solution is aheterogeneous mi+ture, for e+ample, milk. ;ecause of the small siGe of colloidalparticles, we cannot see them with naked eyes. ;ut, these particles can easilyscatter a beam of visible light as observed in activity (.*. his scattering of a beamof light is called the yndall e


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Fig. 2.3: $a% Solution of copper sulphate does not show Tyndall e&ect, $b% mi'ture of water and

mil( shows Tyndall e&ect.

,.3.3 ow can we separate a mi0ture of two immiscible li uids


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Fig. 2.6: Separation of immiscible li)uids


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Fig. 2.8: Separation of dyes in blac( in( using chromatography

Fig.2.9: Separation of two miscible li)uids by distillation


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Fig. 2.13: Water puri cation system in water wor(s

hat you ha5e learnt 4 mi+ture contains more than one substance 5element and$or compound6mi+ed in any proportion.

=i+tures can be separated into pure substances using appropriate separationtechni'ues.


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4 solution is a homogeneous mi+ture of two or more substances. he ma8orcomponent of a solution is called the 9 solvent , and the minor, the 9 solute . he concentration of a solution is the amount of solute present per unit volumeor per unit mass of the solution$solvent. =aterials that are insoluble in a solvent and have particles that are visible to

naked eyes, form a suspension. 4 suspension is a heterogeneous mi+ture. 0olloids are heterogeneous mi+tures in which the particle siGe is too small to beseen with the naked eye, but is big enough to scatter light. 0olloids are useful inindustry and daily life. he particles are called the dispersed phase and themedium in which they are distributed is called the dispersion medium. 1ure substances can be elements or compounds. 4n element is a form ofmatter that cannot be broken down by chemical reactions into simplersubstances. 4 compound is a substance composed of two or more di


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Representation of classification of matter

Is Matter Around us Pure

Matter can be broadly divided into two major groups, 'Pure' and 'Impure'. In chemistry, the term 'purity'acquires quite a different meaning from what we understand it to be in our day-to-day life. ormally,

when we refer to pure water, pure mil!, etc., what is implied is that the water, mil! etc., are free from

harmful substances such as bacteria, fungi, viruses, etc., or are not adulterated. 'Purity' as a chemical

concept signifies something quite different. "hen we say a substance is pure, it means that the

constituent particles that ma!e up the substance are of only one type and have the same chemical

nature. #or e$ample, in chemical terms, pure water implies that it is made of only one type of

molecule i.e., % & . (ccordingly, the chemical classification of matter specifies two main categories of

substances, pure substances and mi$tures )impure substances*.

Matter that is divided into pure and impure substances can be further categori+ed. Pure substances

can be divided into 'elements' and 'compounds' impure substances, commonly called 'mi$tures' can

be further divided into homogeneous' and 'heterogeneous' mi$tures.

Physical and hemical changes in matter In this page we are going to discuss about physical and hemicalchanges in matter concept . Matter undergoes certain changes as a result of theapplication of energy. Water from saltpans on the seacoast dry up, leavingbehind salt; water from the sea evaporates to from water vapour, whichconvert into clouds and then condense to form rain. laciers melt in summerand rivers free!e in winter. A candle upon burning gives light, heat, watervapour and carbon dio"ide. #ydrogen burns in air to form the water molecule# $%.he different changes that matter undergoes, may be broadly classifiedinto &physical& and &chemical& changes.


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Physical changes

"hen the shape, si+e, appearance or state, of a substance is altered, but its

chemical composition remains same a physical

change of matter ta!es place. o new substance is formed. It is usually a change,which is reversible, that is, by reversing the

process, the original substance can be obtained.

/y using a piece of gold, a goldsmith can ma!e a gold chain and can later alter it toma!e a gold bracelet, ring or a pair of

earings. (ll of them consist of the same substance, namely gold. his is an e$ampleof a physical change. ( more common

everyday e$ample is that of water, which can be converted into solid ice, liquid water,and gaseous water vapour. It can be

reconverted to its previous state by various methods. 0et, in all the three forms, thechemical composition of water is not altered.

o new substance with new chemical properties is formed. In all these, waterconsists of two atoms of hydrogen and one atom

of o$ygen.

hus, a Physical change is a change in which the chemical composition of thesubstance is not affected, i.e., no new substance is formed.

1$amples of Physical hanges


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'a( )issolving of sugar in water

"hen crystalline sugar is dissolved in water, it seems to disappear completely, andnot even a very powerful microscope can show us the molecules of sugar in water.he solution obtained is uniformly sweet. /y evaporating the water the sugar can berecovered in a crystalline form.

'b( Magnetising an iron rod

(n iron rod can be converted into a magnet by passing an electric current through aninsulated coil wound around it. "hen the current flows, the iron bar gets magnetised.ne end becomes orth Pole and the other the 2outh Pole. If the direction of the

current is reversed, the orth Pole changes to 2outh Pole and the 2outh Polechanges to orth Pole.

'c( lowing of an electric bulb


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"hen an electric current is passed through the filament of a bulb, the filament startsglowing and the glow stops as soon as the current is cut off. he chemicalcomposition of the filament does not alter in either state.

hemical hange

( change in which the composition of a substance is altered is called as chemicalchange of matter. (s a result, the original

properties get changed and one or more new substances are formed.

Iron is greyish white metal and conducts electricity. It is attracted by a magnet, andreacts with dilute acids to yield hydrogen.

2ulphur is a non-metal, and is yellow in colour. It dissolves in carbon disulphide."hen powdered iron and sulphur are heated

together, a completely new substance, iron sulphide is formed. he properties of ironsulphide are entirely different from those of

iron and sulphur. It is blac! in colour, does not get attracted by a magnet and does

not allow electric current to pass through it.

It reacts with dilute acids to from hydrogen sulphide gas. In short, the properties ofneither iron nor sulphur are e$hibited by iron

sulphide.

onditions #or hemical hange


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he criterion for a chemical change is the production of one or more newsubstances. herefore, certain conditions should be

met in order to bring about a chemical change. he necessary conditions are3

*. ( minimum amount of energy needed to initiate a reaction, called the activationenergy, should be supplied in the form of heat,

light or electric current. In a chemical change the reactants combine to form newproducts. #or this process it is necessary to

brea! the old bonds of the reactants and forms fresh bonds in order to give newproducts. his requires a certain amount of

energy.

$. #or the occurrence of any reaction, the molecules or atoms of the reactants mustcollide with one another, in order to brea!

old bonds and form new bonds.

+. he speed with which the chemical reaction ta!es place is called the rate of thechemical reaction. his should be

appreciable, to bring about the change.

. he rate of a reaction depends on following factors3

-emperature Presence of light Presence of catalyst lectricity Pressure.

-emperature / ertain chemical reactions do not ta!e place at room temperature butoccur readily at a higher temperature. (ccordingly, heat is required to start thereaction e.g. fuels li!e coal and wood only start burning when heated to a certaintemperature called its ignition temperature.

Presence of 0ight / 2ome reactions ta!e place only in light and do not ta!e place indar! e.g. photosynthesis in green plants or reaction between %& and l& to form % l.


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Presence of a 1atalyst / ( catalyst is a substance that increases the rate ofchemical reaction without itself undergoing any change.1$ample3 %ydrogenation ofoils to form fats ta!es place faster, in presence of nic!el.

lectricity / ertain reactions ta!e place with the help of an electric current.1$ample3

4ecomposition of acidulated water to give hydrogen and o$ygen gas

Pressure / 2ome chemical reactions need very high pressure to proceed. #or e.g., inthe commercial manufacture of ammonia from nitrogen and hydrogen by %aber's

process, a pressure of over &55 atmosphere is required, in presence of a catalystiron and a temperature of 675o to 755o .

"amples of 1hemical 1hanges

/elow are the e$amples on chemical changes -

'a( ffect of heat on lead nitrate / 8ead nitrate is a white, crystalline solid. "henheated, it starts decomposing with a

crac!ling sound, producing a reddish brown gas called nitrogen dio$ide, and acolourless gas, o$ygen. ( yellow residue of lead

mono$ide is left behind in the test tube.

'b( Action of concentrated sulphuric acid on sugar / "hen concentrated sulphuricacid is added to sugar, it becomes a

blac! mass of sugar charcoal. he acid removes all the water from the sugar, that is,hydrogen and o$ygen and absorbs it

leaving a residue of spongy carbon.


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'c( Action of sodium on cold water /

"hen a small piece )pea si+e* of sodium is placed in cold water, it darts about on the

water with a hissing sound and produces hydrogen. he water left behind, acquiresthe property of turning red litmus blue. his shows the presence of a basicsubstance, which is sodium hydro$ide


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Physical Change Chemical Change

3o new or di


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"ut fe drops of in! on the atch glass.

$o start heating the bea!er. We do not ant to heat the in! directly. %ou ill seethat evaporation is ta!ing place from the atch glass.

&ontinue heating as the evaporation goes on and stop heating hen you do notsee any further change on the atch glass.

'bserve carefully and record your observations.

We find that in! is a mixture of a dye in ater. hus, e can separate the volatilecomponent (solvent) from its non-volatile solute by the method of evaporation.

ow can "e Separate a Mixture of +wo Misci&le ,i uids$

et us try to separate acetone and ater from their mixture.

a!e the mixture in a distillation flas!. Fit it ith a thermometer.

*rrange the apparatus as sho n in Fig. +.

eat the mixture slo ly !eeping a close atch at the thermometer.

he acetone vaporises, condenses in the condenser and can be collected from thecondenser outlet.

Water is left behind in the distillation flas!.


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his method is called distillation. t is used for the separation of components of amixture containing t o miscible li uids that boil ithout decomposition and havesufficient difference in their boiling points.

o separate a mixture of t o or more miscible li uids for hich the difference in boilingpoints is less than /# 0, fractional distillation process is used, for example, for theseparation of different gases from air, different factions from petroleum products etc.he apparatus is similar to that for simple distillation, except that a fractionating columnis fitted in bet een the distillation flas! and the condenser.

* simple fractionating column is a tube pac!ed ith glass beads. he beads providesurface for the vapours to cool and condense repeatedly, as sho n in Fig. 12.


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ow can "e %&tain ure Copper Sulphate from an ImpureSample$

a!e some (approximately # g) impure sample of copper sulphate in a china dish.

3issolve it in minimum amount of ater.

Filter the impurities out.

4vaporate ater from the copper sulphate solution so as to get a saturated

solution.

&over the solution ith a filter paper and leave it undisturbed at roomtemperature to cool slo ly for a day.

%ou ill obtain the crystals of copper sulphate in the china dish.

his process is called crystallisation.

he crystallisation method is used to purify solids. For example, the salt e get from sea

ater can have many impurities in it. o remove these impurities, the process of crystallisation is used. &rystallisation is a process that separates a pure solid in the form


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of its crystals from a solution. &rystallisation techni ue is better than simple evaporationtechni ue as 5

some solids decompose or some, li!e sugar, may get charred on heating todryness.

some impurities may remain dissolved in the solution even after filtration. 'nevaporation these contaminate the solid.

#pplications

"urification of salt that e get from sea ater.

Separation of crystals of alum (phit!ari) from impure samples.

hus, by choosing one of the above methods according to the nature of the componentsof a mixture, e get a pure substance. With advancements in technology many moremethods of separation techni ues have been devised. n cities, drin!ing ater is suppliedfrom ater or!s. * flo diagram of a typical ater or!s is sho n in Fig. 16.


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http399www.it.iitb.ac.in9e!shi!sha9e ontent-2how.do:documentId;rain is separated from stal!s, while harvesting. Mil! or curd is churned toseparate the butter )#ig. 7.&*. (s we learned in hapter ?, we gin cotton toseparate its seeds from the fibre.

Perhaps you might have eaten salted daliya or poha . If you found that it hadchillies in it, you may have carefully ta!en them out before eating.

2uppose you are given a bas!et containing mangoes and guavas and as!ed toseparate them. "hat would you do: Pic! out one !ind and place them in aseparate container, right:

2eems easy, but what if the materials we want to separate are much smaller

than mango or guava:
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2ig. 3.$ /utter is ta!en out by churning mil! or curds

Imagine you are given a glass of sand with salt mi$ed in it. Impossible, even tothin! of separating salt from this mi$ture by pic!ing out grains of sand by hand@

/ut, why would we need to separate substances li!e this at all, is what Paheliwants to !now.

4ctivity !

"n 'olumn 1 of Table $.1, are gi en a few processes of separation. The purpose of

separation and the way separated components are used is mentioned in 'olumn 2 and !respecti ely. %owe er, the information gi en in 'olumns 2 and ! is 0umbled up. 'anyou match each

Table 5.1 Why do we separate substances?

4eparation processPurpose for which we do

the separationWhat do we do with theseparated components5

=* 2eparat stone from

rice

a* o separate two different,

but useful components

i* "e throw away the solid

components

&* hurning mil! toobtain butter

b* o remove non-usefulcomponents.

ii* "e throw away the impurities.

?* 2eparate tealeaves

c* o remove impurities orharmful components.

iii* "e use both the components.

process with its purpose and the way separated components are used


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"e see that, before we use a substance, we need to separate harmful or non-useful substances that may be mi$ed with it. 2ometimes, we separate evenuseful components if we need to use them separately.

he substances to be separated may be particles of different si+es or materials. hese may be solids, liquids or even gases. 2o, how do we separatesubstances mi$ed together if they have so many different properties:

7.= M1 % 42 # 21P(A( I

"e will discuss some simple methods of separating substances that are mi$edtogether. 0ou may come across some of these methods being used in day today activities.

%and Pic!ing

4ctivity (

ring a packet of grain purchased from a shop to the classroom. ow, spread the grainon a sheet of paper. o you find only one kind of grain on the sheet of paper Are there

pieces of stone, husks, broken grain and particles of any other grain in it ow, remo ewith your hand the pieces of stone, husks and other grains from it.

This method of handpicking can be used for separating slightly larger si-ed impuritieslike the pieces of dirt, stone, and husk from wheat, rice or pulses (3ig. $.!). Theuantity of such impurities is usually not ery large. "n such situations, we find thathandpicking is a con enient method of separating substances.

Fig ! " 7andpicking stones from grain

hreshing

0ou must have seen bundles of wheat or paddy stal!s lying in fields after harvesting the crop. 2tal!s are dried in the sun before the grain is separatedfrom them. 1ach stal! has many grain seeds attached to it. Imagine the


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number of grain seeds in hundreds of bundles of stal! lying in the field@ %owdoes the farmer separate grain seeds from those bundles of stal!s:

ne may pluc! mangoes or guavas from the trees. /ut, grain seeds are muchsmaller than mangoes or guavas. 2o, pluc!ing them from their stal!s would beimpossible. %ow does one separate grain seeds from their stal!s:

he process that is used to separate grain from stal!s is threshing . In thisprocess, the stal!s are beaten to free the grain seeds )#ig. 7.6*.

2ig 3. hreshing

2ometimes, threshing is done with the help of bulloc!s. Machines are alsoused to thresh large quantities of grain.

"innowing

4ctivity *

/ake a mi+ture of dry sand with sawdust or powdered dry lea es. 4eep this mi+ture ona plate or a newspaper. 5ook at this mi+ture carefully. 'an the two differentcomponents be made out easily Are the si-es of particles of the two components

similar 6ould it be possible to separate the components by handpicking

ow, take your mi+ture to an open ground and stand on a raised platform. Put themi+ture in a plate or sheet of paper. %old the plate or the sheet of paper containing themi+ture, at your shoulder height. Tilt it slightly, so that the mi+ture slides out slowly.

6hat happens o both the components 7 sand and sawdust (or powdered lea es) fallat the same place "s there a component that blows away id the wind manage toseparate the two components .


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his method of separating components of a mi$ture is called winnowing ."innowing is used to separate heavier and lighter components of a mi$ture bywind or by blowing air.

2ig. 3.3 "innowing

his method is commonly used by farmers to separate lighter hus! particlesfrom heavier seeds of grain )#ig. 7.7*.

he hus! particles are carried away by the wind. he seeds of grain getseparated and form a heap near the platform for winnowing. he separatedhus! is used for many purposes such as fodder for cattles.

2ieving

2ometimes, we may wish to prepare a dish with flour. "e need to removeimpurities and bran that may be present in it. "hat do we do: "e use a sieveand pour the flour into it )#ig. 7.B*.

2ieving allows the fine flour particles to pass through the holes of the sievewhile the bigger impurities remain on the sieve.

In a flour mill, impurities li!e hus! and stones are removed from wheat beforegrinding it. Csually, a bagful of wheat is poured on a slanting sieve. he sievingremoves pieces of stones, stal! and hus! that may still remain with wheat after threshing and winnowing.


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2ig. 3.6 2ieving

0ou may have also noticed similar sieves being used at construction sites

2ig. 3.7 Pebbles and stones are removed from sand by sieving

to separate pebbles and stones from sand )#ig. 7.


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Aice or pulses are usually washed before coo!ing. "hen you add water tothese, the impurities li!e dust and soil particles get separated. hese impuritiesgo into water, which becomes a little muddy. ow, what will sin! to the bottomof the vessel D rice or dust: "hy: %ave you seen that the vessel is tilted topour out the dirty water:

"hen the heavier component in a mi$ture settles after water is added to it, theprocess is called sedimentation . "hen the water )along with the dust* isremoved, the process is called decantation )#ig. 7.E*. 8et us find a few other mi$tures that can be separated through sedimentation and decantation.

he same principle is used for separating a mi$ture of two liquids that do notmi$ with each other. #or e$ample, oil and water from their mi$ture can beseparated by this process. If a mi$ture of such liquids is allowed to stand for some time, they form two separate layers. he component that forms the toplayer can then be separated by decantation.

8et us again consider a mi$ure of a solid and liquid. (fter preparing tea, whatdo you do to remove the tea leaves: ry decantation. It helps a little. /ut, doyou still get a few leaves in your tea: ow, pour the tea through a strainer.

2ig. 3.8 2eparating two components of a mi$ture by sedimentation and decantation

4id all the tea leaves remain in the strainer: his process is

called filtration )#ig. 7.=*. "hich method of separating tea leaves fromprepared tea is better, decantation or filtration:

8et us now consider the e$ample of water that we use. 4o all of us, at all times,get safe water to drin!: 2ometimes, water supplied through taps may bemuddy. he water collected from ponds or rivers may also be muddy,especially after rains. 8et us see if we can use some method of separation toremove insoluble impurities li!e soil from the water.

4ctivity


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'ollect some muddy water from a pond or a ri er. "f it is not a ailable, mi+ some soilto water in a glass. 5et it stand for half an hour. 9bser e the water carefully and noteyour obser ations.

oes some soil settle at the bottom of water 6hy 6hat will you call this process

ow, slightly tilt the glass without disturbing the water. 5et the water from the top flowinto another glass (3ig. $.:). 6hat will you call this process

"s the water in the second glass still muddy or brown in colour ow filter it. id thetea strainer work 5et us try filtering the water through a piece of cloth. "n a piece of cloth, small holes or pores remain in between the wo en threads. These pores in a clothcan be used as a filter.

"f the water is still muddy, impurities can be separated by a filter that has e en smaller pores. A filter paper is one such filter that has ery fine pores in it. 3ig. $.; shows thesteps in ol ed in using a filter paper. A filter paper folded in the form of a cone is fi+edonto a funnel (3ig. $.1


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boils. his gives a mi$ture of particles of solid paneer and a liquid.he paneer is then separated by filtering the mi$ture through a fine cloth or astrainer.

1vaporation

4ctivity I

%eat a beaker containing some water. Allow the water to boil. "f you continue heating,would the water turn into steam

Fig ! $$ 7eating a beaker containing salt water

and disappear completely ow, add two spoons of salt to water in another beaker andstir it well. o you see any change in the colour of water 'an you see any salt in the

beaker, after stirring %eat the beaker containing the salt water (3ig. $.11). 5et thewater boil away. 6hat is left in the beaker

"n this acti ity, we used the process of e aporation, to separate a mi+ture of water andsalt.

he process of conversion of water into its vapour is called evaporation . he

process of evaporation ta!es place continuously wherever water is present."here do you thin!, salt comes from: 2ea water contains many salts mi$ed init. ne of these salts is the common salt. "hen sea water is allowed to stand inshallow pits, water gets heated by sunlight and slowly turns into water vapour,through evaporation. In a few days, the water evaporates completely leavingbehind the solid salts )#ig. 7.=&*. ommon salt is then obtained from thismi$ture of salts by further purification.


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2ig. 3.*$ btaining salt from sea water

Cse of more than one method of separation

"e have studied some methods for separation of substances from their mi$tures. ften, one method is not sufficient to separate the differentsubstances present in a mi$ture. In such a situation, we need to use more thanone of these methods.

4ctivity 2

Take a mi+ture of sand and salt. %ow will we separate these 6e already saw thathandpicking would not be a practical method for separating these.

4eep this mi+ture in a beaker and add some water to this. 5ea e the beaker aside for some time. o you see the sand settling down at the bottom The sand can be separated

by decantation or filtration. 6hat does the decanted li uid contain o you think thiswater contains the salt which was there in the mi+ture at the beginning

ow, we need to separate salt and water from the decanted li uid. Transfer this li uidto a kettle and close its lid. %eat the kettle for some time. o you notice steam comingout from the spout of the kettle

Take a metal plate with some ice on it. %old the plate 0ust abo e the spout of the kettleas shown in 3ig. $.1!. 6hat do you obser e 5et all the water in the kettle boil off.

6hen the steam comes in contact with the metal plate cooled with ice, it condenses andforms li uid water. The water drops that you obser ed falling from the plate, were dueto condensation of steam. The process of con ersion of water apour into its li uidform is called condensation .

id you e er see water drops condensed under a plate that has been used to co er aessel containing milk that has 0ust been boiled

After all the water has e aporated, what is left behind in the kettle


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6e ha e thus, separated salt, sand and water using processes of decantation, filtration,e aporation and condensation.

Paheli faced a problem while reco ering salt mi+ed with sand. 8he has mi+ed a packetof salt in a small

Fig ! $" Dvaporation and condensation

amount of sand. 8he then tried the method suggested in Acti ity =, to reco er the salt.8he found, howe er, that she could reco er only a small part of the salt that she hadtaken. 6hat could ha e gone wrong

an water dissolve any amount of a substance:

In chapter 6, we found that many substances dissolve in water and form asolution. "e say that these substances are soluble in water. "hat will happenif we go on adding more and more of these substances to a fi$ed quantity of water:

4ctivity /

>ou will need a beaker or a small pan, a spoon, salt and water. Pour half a cup of water

in the beaker. Add one teaspoonful of salt and stir it well, until the salt dissol escompletely (3ig $.1#). Again add a teaspoonful of salt and stir well. ?o on adding salt,one teaspoonful at a time, and stir.

After adding a few spoons of salt, do you find that some salt remains undissol ed andsettles at the bottom of the beaker "f yes, this means that no more salt can be dissol edin the amount of water we ha e taken. The solution is now said to be saturated .

%ere is a hint as to what might ha e gone wrong when Paheli tried to reco er largeuantity of salt mi+ed with sand. Perhaps the uantity of salt was much more than that

re uired to form a saturated solution. The undissol ed salt


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Fig ! $& #issolving salt in water

would ha e remained mi+ed with the sand and could not be reco ered. 8he could sol e

her problem by using a larger uantity of water.

8uppose, she did not ha e sufficient uantity of water to dissol e all the salt in themi+ture. "s there some way that water could be made to dissol e more salt before thesolution gets saturated5et us try and help Paheli out.

4ctivity

Take some water in a beaker and mi+ salt in it until it cannot dissol e any more salt.This will gi e you a saturated solution of salt in water.

ow, add a small uantity of salt to this saturated solution and heat it. 6hat do youfind 6hat happens to the undissol ed salt in the bottom of the beaker oes itdissol e, now "f yes, can some more salt be dissol ed in this solution by heating it

5et this hot solution cool. oes the salt appear to settle at the bottom of the beaker again

The acti ity suggest that larger uantity of salt can be dissol ed in water on heating.

oes water dissol e e ual amounts of different soluble substances 5et us find out.

4ctivity !"

Take two glasses and pour half a cup of water in each of them. Add a teaspoon of saltto one glass and stir till the salt dissol es. ?o on adding salt, one teaspoon at a time, tillthe solution saturates. @ecord the number of spoons of salt that dissol ed in the water,in Table $.2. ow, repeat the same acti ity with sugar. @epeat this with some other substances that are soluble in water.

6hat do you notice from Table $.2 o you find that water dissol es differentsubstances in different amounts


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Table 5.2

4ubstance 9umber of spoons of substance that dissolved in water

2alt

2ugar

"e have discussed a few methods of separating substances. 2ome of themethods of separation presented in this chapter are also used in a sciencelaboratory.

"e also learnt that a solution is prepared by dissolving a substance in a liquid. ( solution is said to be saturated if it cannot dissolve more of the substance init.

: W%R)4

hurning

ondensation

4ecantation

1vaporation

#iltration

%andpic!ing

2aturated solution

2edimentation

2ieving

2olution

hreshing

"innowing

4ummary

%andpic!ing, winnowing, sieving, sedimentation, decantation and filtration are someof the methods of separating substances from their mi$tures.


43/46

%us! and stones could be separated from grains by handpic!ing.

%us! is separated from heavier seeds of grain by winnowing.

4ifference in the si+e of particles in a mi$ture is utilised to separate them by the

process of sieving and filtration.

In a mi$ture of sand and water, the heavier sand particles settle down at the bottomand the water can be separated by decantation.

#iltration can be used to separate components of a mi$ture of an insoluble solid anda liquid.

1vaporation is the process in which a liquid gets converted into its vapour.1vaporation can be used to separate a solid dissolved in a liquid.

( saturated solution is one in which no more of that substance can be dissolved.

More of a substance can be dissolved in a solution by heating it.

"ater dissolves different amount of soluble substances in it.

DJD@0&>D

!. %hy do we need to separate di


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o 6hen milk, cooled after boiling, is poured onto a piece of cloth the cream(malai ) is left behind on it. This process of separating cream from milk isan e+ample of .

o 8alt is obtained from seawater by the process of .

o "mpurities settled at the bottom when muddy water was kept o ernight in a bucket. The clear water was then poured off from the top. The process of separation used in this e+ample is called .

. rue or false?

4.9o %ption -ruerain and hus! can be separated with the process ofdecantation.

rue

#alse

2how Aesult


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1hould you add ice to the lemonade before or afterdissolving sugar? &n which case would it be possible to dissolve more sugar?

4uggested Pro=ects and Activities

=. Fisit a nearby dairy and report about the processes used to separate cream frommil!.

&. 0ou have tried a number of methods to separate impurities li!e mud from water.2ometimes, the water obtained after employing all these processes could still be alittle muddy. 8et us see if we can remove even this impurity completely. a!e thisfiltered water in a glass. ie a thread to a small piece of alum. 2uspend the piece ofalum in the water and swirl. 4id the water become clear: "hat happened to the mud:his process is called loading. al! to some elders in your family to find out whetherthey have seen or used this process.

-hings -o 4ee

G he winnowersH, painted by >ustav ourbet in =E7?

Aeproduced with permission from Muse de /eaus (rts, antes, #rance


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Physical Nature of Matter

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