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CBSE Class–VI Subject Science Revision Notes CHAPTER – 5
Separation of Substances
PURE SUBSTANCES : substances which contain only onekind of particles .
IMPURE SUBSTANCES : substances whichcontain more thanone kind ofparticles .
ELEMENT : A substance madefrom identical particles of one material.
COMPOUND : A substance formed as a result of chemical combination of two ormore
elements ina fixed ratio.
A solution is a mixture of two substances. the substance inlarger quantity isthe solvent and
the otheris the solute.
Elements and compounds are pure substances.
NEED FORSEPARATING COMPONENT OFA MIXTURE
removing harmful or unwanted components, and
obtaining useful and desire component in pure form.
Methods ofseparation are
Threshing, winnowing, handpicking, sieving,
magnetic separation, floating and sinking method,
sedimentation and decantation loading,
filtration,separation to immiscible liquids, churning toseparate cream frommilk,
sublimation.
(i) Separation of solid fromother solids:
(a) Threshing: Theprocess of separating grain from huskor chaff is called threshing.
Chaff :pieces of straw ; waste material of agriculture processes.
(b) Winnowing: Theprocess of separation of heavier andlighter components ofa mixture
by windor blowing air.
(c) Hand-picking: The process by which undesirable components are justpicked up byhand.
(d) Sieving: Theprocess by whichseparate solid constituents of a mixture which differ in
their sizes.
A sieve is a device withmany small holesin it , which allowthe smaller particles to pass
through.
(e) Magnetic separation: Process bywhich magnet is moved oversuch a mixture, the
magnetic material sticks to itand is removed.
(ii) Separation of water soluble solids or separating solute soluble insolvent:
(a) Evaporation: Process bywhich the conversion of liquid state into gaseous state on heating.
(b) Condensation: Process bywhich conversion ofgaseous state intoliquid state oncooling.
(iii) Separation of insoluble solids from Liquids:
(a) Sedimentation: The process of settling downof heavier andinsoluble component from
mixture is called sedimentation.. Example: sand, water.
(b) Decantation: The process of transferring cleanliquid without disturbing the sediment, is called decantation.
(c) Loading: Themethods by which finer particles aremade to settle faster by dissolving a
small quantity of alum.
(d) Filtration: In thisprocess the impurities are passed through a filter. Thefilter has poresin it thatallow only liquids to pass through ; it canseparate the suspended particles or solid
particles.
The clear liquid so obtained is called thefiltrate an theleft over material on the filter
paper isknown as residue.
(iv) Separation of Immiscible Liquids:
IMMISCIBLE :- whentwo liquids donot mix wellwith one another.
(a) Funnel: The method of separating mixture of oil andwater.
(b) Centrifugation: The method in which mixture containing suspended particles is rotated at a high speed in a centrifuge and heavier particles settle down. It is used for separating creamfrom milk.
(c) Churning: The method which is usedfor separating lighter particles of solid suspended in
a liquid. Example: butter fromcurd.
SEPARATING SOLUTE NOT SOLUBLE INA SOLVENT
Flotation and sinking methods :- This method is used whenthe components arenot soluble inwater and oneof the component of a mixture is lighter thanwater an theother is heavier
than water.
SUBLIMATION :-The changing of a soliddirectly to vapour, without coming toliquid state is called sublimation. · Husk and stones could be separated fromgrains by handpicking. · Husk is separated from heavier seeds of grain bywinnowing. · A saturated solution is one inwhich no moreof that substance can be dissolved. · More of a substance canbe dissolved ina solution byheating it. · Water dissolves different amount of soluble substances in it.
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