Separation of Substances I

1 5 Separation of SubstancesGrain is separated from stalks, whileharvesting. Milk or curd is churned toseparate the butter (Fig. ). As welearned in Chapter 3, we gin cotton toseparate its seeds from the you mighthave eaten salteddaliya or poha. If youfound that it hadchillies in it, you mayhave carefully takenthem out before you are given a basketcontaining mangoes and guavas andasked to separate them. What would youdo? Pick out one kind and place themin a separate container, right?Seems easy, but what if the materialswe want to separate are much smallerFig. Separating tea leaves with a strainerFig. is taken out by churning milk orcurdBut, why would we need toseparate Substances like thisat all, is what Paheli wantsto 1In Column 1 of Table , are given afew processes of Separation .

2 The purposeof Separation and the way separatedcomponents are used is mentioned inColumn 2 and 3 respectively. However,the information given in Columns 2 and3 is jumbled up. Can you match eachIn our daily life, there are many instances when we notice a substance being separated from a mixtureof leaves are separated from theliquid with a strainer, while preparingtea (Fig. ).than mango or guava? Imagine you aregiven a glass of sand with salt mixed init. Impossible, even to think ofseparating salt from this mixture bypicking out grains of sand by hand!2021 2236 SCIENCE process with its purpose and the wayseparated components are used?We see that, before we use asubstance, we need to separate harmfulor non-useful Substances that may bemixed with it.

3 Sometimes, we separateeven useful components if we need touse them Substances to be separated maybe particles of different sizes ormaterials. These may be in any threestates of matter , solid, liquid or , how do we separate substancesmixed together if they have so manydifferent properties? METHODS OF SEPARATIONWe will discuss some simple methods ofseparating Substances that are mixedtogether. You may come across some ofthese methods being used in day to 2 Bring a packet of food grain purchasedfrom a shop to the classroom. Now,spread the grains on a sheet of you find only one kind of grain onthe sheet of paper? Are there pieces ofstone, husks, broken grain and particlesof any other grain in it? Now, removewith your hand the pieces of stone,husks and other grains from method of handpicking canbe used for separating slightly largersized impurities like the pieces of dirt,stone, and husk from wheat, rice orpulses (Fig.)

4 The quantity of suchimpurities is usually not very such situations, we find thathandpicking is a convenient method ofseparating Why do we separate Substances ?noitarapeSssecorpodewhcihwrof esopruPnoitarapesehtehthtiwodewodtahW?st nenopmocdetarapesetarapeS)1ecirmorfsenot s,tnereffidowtetarapesoT) ) )2rettubniatbootlufesu-nonevomeroT) ) )3sevaelroseitirupmievomeroT) ) Handpicking stones from grainThreshingYou must have seen bundles of wheator paddy stalks lying in fields after2021 2237 Separation OF Substances harvesting the crop. Stalks are dried inthe sun before the grain is separatedfrom them. Each stalk has many grainseeds attached to it. Imagine thenumber of grain seeds in hundreds ofbundles of stalk lying in the field! Howdoes the farmer separate grain seedsfrom those bundles of stalks?

5 One may pluck mangoes or guavasfrom the trees. But, grain seeds aremuch smaller than mangoes or , plucking them from their stalkswould be impossible. How does oneseparate grain seeds from their stalks?The process that is used to separategrain from stalks etc. is threshing. Inthis process, the stalks are beaten to freethe grain seeds (Fig. ). Sometimes,this mixture on a plate or a at this mixture carefully. Can thetwo different components be made outeasily? Are the sizes of particles of thetwo components similar? Would it bepossible to separate the components byhandpicking?Now, take your mixture to an openground and stand on a raised the mixture in a plate or sheet ofpaper. Hold the plate or the sheet ofpaper containing the mixture, at yourshoulder height.

6 Tilt it slightly, so thatthe mixture slides out happens? Do both thecomponents sand and sawdust (orpowdered leaves) fall at the same place?Is there a component that blows away?Did the wind manage to separate thetwo components?This method of separatingcomponents of a mixture is calledwinnowing. Winnowing is used toseparate heavier and lighter componentsof a mixture by wind or by blowing Threshingthreshing is done with the help ofbullocks. Machines are also used tothresh large quantities of 3 Make a mixture of dry sand withsawdust or powdered dry leaves. KeepFig. Winnowingsoophuskgraindirection of the air2021 2238 SCIENCEThis method is commonly used byfarmers to separate lighter husk particlesfrom heavier seeds of grain (Fig.)

7 The husk particles are carried awayby the wind. The seeds of grain getseparated and form a heap near theplatform for winnowing. The separatedhusk is used for many purposes suchas fodder for , we may wish to prepare adish with flour. We need to removeimpurities and bran that may be presentin it. What do we do? We use a sieveand pour the flour into it (Fig. ).Sieving allows the fine flour particlesto pass through the holes of the sievewhile the bigger impurities remain onthe a flour mill, impurities like huskand stones are removed from wheatbefore grinding it. Usually, a bagful ofwheat is poured on a slanting sieve. Thesieving removes pieces of stones, stalkand husk that may still remain withwheat after threshing and separate pebbles and stones fromsand (Fig.)

8 Activity 4 Bring a sieve and a small quantity offlour from home, to the class. Sieve theflour to separate any impurities in , make a fine powder of chalk piecesand mix it with the flour. Can weseparate the flour and the powderedchalk by sieving?Sieving is used when components ofa mixture have different , Decantationand FiltrationSometimes, it may not be possible toseparate components of a mixture bywinnowing and handpicking. Forexample, there may be lighter impuritieslike dust or soil particles in rice orpulses. How are such impuritiesseparated from rice or pulses beforecooking?Rice or pulses are usually washedbefore cooking. When you add water tothese, the impurities like dust particlesFig. SievingYou may have also noticed similarsieves being used at construction sitesFig.

9 Pebbles and stones are removed fromsand by sieving2021 2239 Separation OF SUBSTANCESget separated. These impurities go intowater. Now, what will sink to the bottomof the vessel rice or dust? Why? Haveyou seen that the vessel is tilted to pourout the dirty water?When the heavier component in amixture settles after water is added toit, the process is called the water (along with the dust) isremoved, the process is calleddecantation (Fig. ). Let us find afew other mixtures that can be separatedthrough sedimentation same principle is used forseparating a mixture of two liquids thatdo not mix with each other. For example,oil and water from their mixture can beseparated by this process. If a mixture ofsuch liquids is allowed to stand for sometime, they form two separate layers.

10 Thecomponent that forms the top layer canthen be separated by us again consider a mixure of asolid and liquid. After preparing tea,what do you do to remove the tea leaves?Usually, we use stainer to remove tealeaves. Try decantation. It helps a , do you still get a few leaves in yourtea? Now, pour the tea through astrainer. Did all the tea leaves remainin the strainer? This process is calledfiltration (Fig. ). Which method ofseparating tea leaves from prepared teais better, decantation or filtration?Let us now consider the exampleof water that we use. Do all of us, atall times, get safe water to drink?Sometimes, water supplied through tapsmay be muddy. The water collected fromponds or rivers may also be muddy,especially after rains.