colloids.pptx

8/17/2019 Colloids.pptx

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Colloids

1Errors and Ommissions areexpected


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“It is heterogenous solution in which aparticulate matter known as dispersed phase(dispersoid) is distributed throughout thecontinuous or dispersion medium.”

Or

It is the mixture with properties in between thoseof a solution and ne suspension.

!ord colloid comes from "reek word “kolla”which means glue.

#ispersed s$stem is classied on the basis of theparticle si%e of the dispersed material.

Errors and Ommissions areexpected

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Dispersion Systems


'

#ispersed

$stem

Ionic

s$stem orolecular#ispersion

*olloidal#ispersion

*oarse#ispersion


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1. Ionic or MolecularDispersion

the si%e of dispersed phase ordispersoid is +1nm.

#ispersoid is ,isible in ultra-microscope.

ma$ pass through ultra-lters.

can rapidl$ diuse.

Examples:

olution of /a*l in water.

olution of glucose in water.


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2. Col lo idalDispersion

the si%e of dispersed phase is 1nm-1nm.

dispersed phase ma$ pass through ordinar$lter paper but can2t pass through ultra-

lters (animal membranes or permeablemembranes).

Examples:

ingle large molecule of protein.

"roup of small molecules i.e. colloidalsolution of gold.


3


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3. Coarse Dispersion

dispersoid si%e is greater than 1nm.

can2t pass through ordinar$ lter paper.

4hese particles can2t diuse.

Examples:

5articles of bismith carbonate in a6ueoussuspension.

"rains of sand.ost pharmaceutical emulsions and

suspensions.


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Comparison of Properties of Solution, Colloids andSuspensions

Properties Solution Colloid Suspension

Particle sie + 1nm 1 8 1 nm 9 1nm

!ppearance *lear *loud$ *loud$

"omo#eneity :omogenous :omogenous or:eterogenous

:eterogenous

$ransparency Often transparentbut often colored

Often translucentand opa6ue butcan be

transparent

Often opa6ue butcan betranslucent

Separation #oes notseparate

#oes notseparate

eparates orsettles

%iltera&ility 5ass throughlter paper

5ass throughlter paper

5articles don2tpass throughlter paper


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$ypes of Colloids

$ypes of ColloidsDispersedParticles

DispersionMedium

'ame Examples

(as eaten egg white?ha,ing *ream?whipped cream? ice

cream soda(as olid olid foam @ubber foam?arshmallow

)i*uid "as


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Colloidal Dispersion

*olloids are substances consisting of a continuousmedium and particles of a discontinuous medium ha,ing

si%e of 1-1nm.

ilk? ink? sulphur? starch? gum and blood are examples of

colloids.If the dispersed phase is solid and the dispersion medium

is li6uid then it is called as “colloidal suspension”

if both of the medium are li6uid then it is called as

colloidal emulsion.

colloidal dispersion of a substance is an intermediatestage between true homogenous solution and the coarsesuspension.


B


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Sie and S+ape

5roperties and beha,iour ofcolloids depends chieC$upon the si%e? shape andcharge of the dispersedparticles.

4he color of the colloidaldispersion depends uponthe si%e of the particles.

>ecause of the si%e?colloidal particles can beseparated b$ultralteration? >uchnerchannel and Electrodial$sis.


1


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Class i cation

1 . ) y o p + i l i c C o l l o i d s :

$stems in which colloidal particles interact withdispersion medium.


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Class i cation

2. )yop+o&ic Colloids:


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Class i cation

3. !mp+ip+ilic or !ssociation Colloids:

dispersed phase consists of aggregates (micelles) of smallorganic molecules of ions whose si%e indi,iduall$ is belowthe colloidal range are termed as association colloids.

mphiphiles are also called as surface acti,e agents.

!hen these are present in low conc. these form truesolution due to sub-colloidal si%e.

when conc. is increased? aggregation occurs o,er thenarrow range of conc.

4he conc. at which the micelles formation takes place iscalled as critical micelle conc. “**”.

4he no. of monomers that aggregate to form a micelle isknown as “aggregation number”.


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Class i cation

=ormation ofmicelles at ** iscalled

“micelli%ation”.pherical micelles

exist at conc. closeto **.

t high conc.laminar micellesexist in e6uilibrium

with sphericalmicelles.Errors and Ommissions are

expected10


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Classication of!mp+ip+iles

$ype Compound !mp+ip+ile (e#enion

!nion odium laur$l sulfate *:'(*:&)11OO'- /aF

Cation *et$l trimeth$lammonium bromide

*:'(*:&)13/F(*:')' >r

-

'on-ionic

5ol$ox$eth$lene laur$lether

*:'(*:&)1*:&O(*:&O*:&)&

':

!mp+olytic

#imeth$ldodec$lammonium propanesulfonate

*:'(*:&)11/F

(*:')&(*:&)'OO'-


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Comparison of Properties of DierentClasses of Colloidal Dispersions

Properties )yop+ilicColloid

)yop+o&icColloid

!mp+ip+ilicColloid

DispersedP+ase

*onsist of largeorganicmolecules

ha,ing si%ewithin colloidalrange.

*onsist ofmainl$inorganic

particles suchas gold orsil,er.

*onsist ofaggregate(micelle) of

small organicmolecules ofions whose si%eindi,iduall$ isbelow thecolloidal range.

Dispersa&ility #isperse easil$on stirring toform colloidalsolution.

#on2t disperseeasil$ and forpreparationspecial methodsare used.

ggregates arespontaneousl$formed fromsolution whenconc. ofmphiphiles

exceeds **.Errors and Ommissions areexpected 17


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)yop+o&icColloid

!mp+ip+ilicColloid

Sol/ation sol,atedreadil$.


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)yop+o&icColloid

!mp+ip+ilicColloid

%arady$yndalEect

bsent or ,er$weak.

strong lmost absent.

0iscosity Giscosit$ of

dispersionmedium isincreased b$ thepresence ofdispersedphase. t

suHcientl$ highconc. solutionma$ remain as agel.

Giscosit$ of

dispersionmedium is notincreased b$ thepresence ofl$ophobiccolloidal

particles.

Giscosit$ of the

s$stemincreases as theconc. of themphiphileincreases.

Sta&ilitytoards

electrolyte

table in thepresence of

electrol$te.

not stable in thepresence of

e,en smallconc. of

In a6ueoussolutions? the

** is reducedb$ the presenceErrors and Ommissions are

expected1A


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)yop+o&icColloid

!mp+ip+ilicColloid

Irre/ersi&ilityafterprecipitation

@e,ersible Irre,ersible

Sta&ilitytoardsprolon#eddialysis

stable nstable. nstable

Protecti/e!&ility

*apable ofacting asprotecti,ecolloids.

Incapable ofacting asprotecti,ecolloids andoften re6uirethe addition ofmaterial forstabilit$.

Incapable ofacting asprotecti,ecolloids.


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Properties of colloids

1. Electrical 5roperties.

&. Optical 5roperties.

'. Jinetic 5roperties.


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D e/e l op men t o f C+ a r# eo f Co l l o i d a l Pa r t i c l es

1. Dissociation of t+e adsor&ed molecularelectrolytes:

molecules thus adsorbed on the surface of colloidalparticles ma$ undergo dissociationKioni%ation and

ma$ impart charge to them. during the preparation of sulphide sols. :&

molecules get adsorbed on colloidal particles.

:& molecules thus adsorbed undergo ioni%ation

and release :F ions into the medium. *onse6uentl$? colloidal particles are left with

negati,e charge.


&&


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2. dissociation of molecules formin#colloidal a##re#ates:

aggregates of colloidal dimensions

ma$ themsel,es undergo dissociationKioni%ation resulting in the de,elopmentof charge on the colloidal particles

formed b$ their aggregation.soap molecules (@*OO/a) dissociate to

gi,e @*OO- and /aF ions.


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3. Preferential adsorption of ions fromsolutions:

colloidal particle usuall$ adsorbs those ionswhich are in excess and are common to its ownlattice.

when a ferric h$droxide sol is prepared b$ theh$drol$sis of ferric chloride in warm water? thecolloidal particles of =e(O:)' formed ha,e a

tendenc$ to adsorb preferentiall$ the =e'F ionspresent in the solution. 4his is because =e'F ionsare common to the lattice of =e(O:)' particle.


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1. Positively charged sols:

etallic h$droxide sols e.g.? =e(O:)'?

l(O:)'? *r(O:)'? etc. haemoglobin?sols of basic d$es such as meth$leneblue etc.

2. Negatively charged sols:It includes starch sol? sols of acidd$es such as *ongo red etc.


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1. E lectr icPropert ies

I. Electrop+oresis:

“o,ement of electricall$ charged particles under theinCuence of an applied electrical eld is called aselectrophoresis”.

Electrophoresis is used toeparate a mixture of colloids of dierent charges.

4o determine the 6uantitati,e measurement of rate ofmigration of colloidal particles. Electrophoretic mobilit$i.e. rate in centimetersKsec under a potential of 1,Kcm can

be calculated b$ determining the time necessar$ for asolution to tra,el a denite distance.

for the anal$sis of proteins? nucleic acids andpol$saccharides.


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II. Electro-osmosis:

“o,ement ofelectricall$ chargedparticles under the

inCuence of an appliedelectrical eld througha semipermeablemembrane”.

It is used in theremo,al of water frommoist cla$ and dr$ingd$e pastes.


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III. Streamin# Potential:

if gal,anometer is attached instead ofbatter$? no current Cows.

when water is forced through the tube someemf is indicated.

5otential produced is directl$ proportional tothe applied pressure and %eta potential of

interface. 4his potential is called as streaming

potential.


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I0. Sedimentation Potential:

“In a resting li6uid? particles mo,edue to the gra,itational force andsettle down.

a potential dierence is createdbetween the top and bottom of the

li6uid.5otential dierence between top and

bottom due to sedimentation is

called as sedimentation potential”.Errors and Ommissions areexpected &B


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2. pt icalPropert ies

I. %araday $yndall Eect:

!hen a strong beam of light is passed througha colloidal solution against a dark background

at right angle to the plane of obser,ation? thelight ra$s passing through the dispersion forma ,isible cone? resulting forms the scattering oflight b$ colloidal particles.

lthough the particles cannot be seen directl$?the bright spots? corresponding to particles canbe obser,ed and counted.


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2. pt icalPropert ies

II. )i#+t Scatterin#:

cattering ma$ be described in terms ofrelati,e turbidit$? 4.

the fractional decrease in intensit$ due toscattering as the incident light passesthrough 1cm of solution.

It ma$ be expressed as the intensit$ of light

scattered in all direction? di,ided b$ theintensit$ of the incident light.

4 M IsKI


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3. inetic Properties

I. 4ronian Mo/ement:

@obert >rown studied this phenomenon.

*olloidal particles mo,e in %ig%ag fashion whenparticles of dispersion medium undergo collision

from all sides. >rownian mo,ement keeps colloidal particles

suspended against gra,itation thus makes dispersionpermanent.

Giscosit$ is the expression for the internal resistanceof a Cuid to Cow.

Increasing the ,iscosit$ of the medium? there is adecrease and nall$ stops the >rownian motion.


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II. smotic Pressure:

Osmotic pressure is in,ersel$proportional to the molecular weight.

Osmotic pressure? N M @4

colloids with greater molecularweight ha,e less osmotic pressure.

4hat2s wh$ osmotic pressure of ureais greater as compared to that ofalbumin or starch.


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III. Diusi&ility:

#iusion is the spontaneous mo,ement of molecules from thearea of higher conc. to the area of lower conc. until the conc. ofthe s$stem is uniform throughout is called as diusion.

Fick’s Law of Diusion:

@ate of diusion across the plane is proportional to the concgrandient across the plane to the area of the plane.

M # (*a 8 *b) K PQ

M Cow of solute from region to region >

#M diusion coeHcient of solute in gi,en sol,ent

M cross sectional area through which Cow of solute is measured

P*M change in conc in region and region >

PQM #istance between region and region >


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I0. Sedimentation:

#epending upon the relati,edensities of the dispersed phase? onewill ne the downward mo,ement ofparticles? with in a period of timeranging from few seconds to few

hours. 4his process is called assedimentation.

G M d& (R-RS)gK1AT

" M acceleration due to gra,it$Errors and Ommissions areexpected '3


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0. 0iscosity:

Giscosit$ is an expression of the internalresistance of the Cow of a s$stem under an

applied stress. 4he more ,iscous a li6uid? greater would be

the applied force re6uired to make it Cowat a particular rate.

4he ,iscosit$ of colloidal dispersion isaected b$ the shape of particles of thedisperse phase.


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0I. %iltration:

*olloidal solution cannot pass through ultralters butpass through ordinar$ lter paper.

0II. Eect of $emperature:

!ith the change of temperature? colloids areprecipitated e.g. fried egg and coagulated casein ofmilk.

%locculation 0alue:

“It is the minimum conc. of an electrol$te which isable to cause a decrease in the degree of dispersion?

if the solution is obser,ed two phase after addition ofelectrol$te.”


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Sensitiation 5 Protecti/e !ctionof Colloids

!hen a small amount of h$drophilic or h$drophobiccolloid is added in h$drophobic colloid of oppositecharge? coagulation occurs.

4his phenomenon is called as sensiti%ation.

4he addition of large amount of h$drophile(h$drophilic colloid)? howe,er? stabili%es the s$stem(retards the precipitation of h$drophilic solution).

4his phenomenon is known as protection.

It is belie,ed that protecti,e action is due to theco,ering of l$ophobic particles with that of l$ophiliccolloids.


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Sensitiation 5 Protecti/e !ctionof Colloids

(old 'um&er:

minimum weight in milligram of a protecti,ecolloid (dr$ weight of dispersed phase) re6uiredto pre,ent a color change from red to ,iolet in1ml of a gold solution on the addition of 1ml ofa 1U solution of sodium chloride (/a*l).

Con#o ru&in num&er:

minimum no. of protecti,e colloid in mg thatpre,ents the color change of 1ml of .1Ucongo rubin d$e to which .17gm e6ui,alent ofJ*l is added.


'B


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Sta&ility of Colloids

tabilit$ depends upon the charge? sal,ation and>rownian motion.

rownian mo,ement counteracts the force of gra,it$on the colloidal particles and thus stabili%es thecolloidal s$stem.


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4he aHnit$ of h$drophilic colloidal particle for ana6ueous dispersion medium is suHcient torender these dispersions thermod$namicall$stable e.g. colloidal solution of acacia. "elatin?

starch and proteins form h$drolhilic colloids.#egree of h$dration ma$ ,ar$ among these

compounds.

4here are two main factors incol,ed in the

stabilit$ of colloidsV

i. Electric *harge

ii. :$dration of dispersed particles.


01


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If the charge on the dispersed particles is reducedto %ero? the colloidal s$stem ma$ becomeunstable.

s the colloids pass through isoelectric point? the

charge of each double la$er is re,ersed.fter the h$drophilic colloid is deh$drated it is as

sensiti,e to electrol$tes as h$drophobic colloids.

:eat? alcohol and tannins are used as deh$drating

agents.>oth factors pla$ a ,ital role in stabilit$ of colloids.

Errors and Ommissions areexpected 0&


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imilarl$? if electrol$tes are added in starchsolution.

It will cause remo,al of charges from particles butthere would be no coagulation.

=urther addition of alcoholD a deh$drating agent willcause the precipitation of solution.

o? it can be concluded thatD

i. It is immaterial? in which se6uence the stabilit$

factors are remo,ed.ii. @emo,al of one factor has no e,ident eect but

the remo,al of both factors will cause coagulation.

Errors and Ommissions areexpected 0'


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1. 0ander 6aals forces or Electroma#netic%orces of !ttraction:

due to interaction of permanent dipole andinduced dipole.

4o o,ercome these attraction forces? repulsi,eforces are generated b$ two means.

i. #ue to electric double la$er or surface charge ofparticles.

ii. #ue to interaction bKw adsorbed pol$meric la$ers..bo,e two sources are called electric stabili%ation?

or stearic or pol$meric stabili%ation.

Errors and Ommissions areexpected 00


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2. Electrical %orces of 7epulsion:

4he repulsi,e energ$ G@ arising from the introduction of electrical

double la$ers.

free energ$ of s$stem of two double la$ers as a functions of theirdistance of separation.

3. 4orn 7epulsi/e %orces 807 4orn9:

due to close approach of particles ha,ing irregular surface. *auseof this force is the electron cloud.

. Sol/ation %orces 87epulsi/e9:

4hese are due to presence of strongl$ adsorbed molecular la$ers

of water on each particle.;. Stearic %orces:

uch forces are dependent upon geometr$ and conguration ofmolecules at interface.


$+ El t i l D &l


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$+e Electrical Dou&le)ayer

2 M5article surface

2-aa2Madsorbed particles

aa2-bb2Mstern la$er

bb2-cc2M"ou$ la$er

aa2-cc2Mdiused double la$er

*harge on stern la$er aa2-bb2depends upon the charge onparticles.

If the si%e of the particle is small?there will be increase in surfacearea and surface potential will

be more but smaller particlesaggregate to form largerparticles the surface area isdecreased and decreasedsurface tension.


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F-F-F-F-F-F-F-F-F-F-F-

2

$+ El t i l D &l


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*ations particles are attached to the surface of the particle. 4he adsorbed ions (F,e or-,e) that ga,e the surface its charge(F,e or-,e) are referred as the “5otential #etermining Ions”.

/ext to this there is a la$er of tightl$ bound sol,ent moleculesanions. It is the limiting line. 4hese ions ha,ing a charge

apposite to the potential determining ions and are known as“counter ions or gegenions”.

=irst tightl$ bound la$er extending from aa2 to bb2 is called as“stern la$er”.

econd la$er extending from bb2 to cc2 that is more diused is

called as “"ou$2s la$er”. 4he potential at the solid surface act due to potential

determining Woins is the electrothermod$namic E and is calledas “/ernst 5otential”.

Errors and Ommissions areexpected 0A

S li t % t f D)0


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Salient %eatures of D)0$+eory

In a dispersion s$stem? forces acting on colloidal particlesare mainl$ of two t$pes.

i. Electrostatic repulsion.

ii.


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Salient %eatures of D)0$+eory

5rimar$ minimumis due to the factthat repulsi,e

forces fall o ,er$rapidl$ withdistance (1 nmapprox.) than do

the attracti,eforces.


P ti f C ll id l


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Preparation of ColloidalSolution

1. )yop+ilic Colloids:


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2. )yop+o&ic Colloids:


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i. Dispersion Met+od:

. In this method? large macro si%edparticles are broken down to colloidal

si%e. It includes three methodsDa. P+ysical Met+od:

.


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&. Mec+anical Dispersion:

coarse suspension of a substance in a dispersionmedium is passed through a colloidal mill.

4he two discs of mill rotate in ,er$ high speed in opposite

direction. *oarse dispersion due to powerful shearingforce is con,erted to colloidal si%e e.g. colloidal karolin?XnO and sulphur etc.

c. Electro-Dispersion:

etals can often be dispersed b$ forming an electric arc

under water between electrodes of the metal. 4he metalis ,apori%ed b$ the heat of act? and ,apours condensedinto particles of colloidal si%e due to the coldness of ice

surrounding s$stem.


Preparation of Colloidal


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II. Condensation:

5rinciple of this method is that “ionsand molecules of sub-colloidal range

present in solution are con,erted intoinsoluble particles of colloidal si%e b$means of chemical reaction”. 4hese

important chemical reactions are asfollowsD




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a. "ydrolysis:

olutions of h$droxides of weak metals such as=e? *r? l and n are prepared b$ dissol,ingtheir salts in water.

=erric oxide =e&O'.':&O solution is prepared b$

pouring a solution of =e*l' into boiling water.

:$drol$sis is also used to prepare solution of

lminium? chromium and other metal oxides.&=e*l' F 7:&O =e&O'.':&O F 7:*l




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II. xidation:

ulphur solution is prepared b$ mixing :& and O&.

&:& F O& &:&O F

III. 7eduction:

!hen gold chloride is reduced with n*l& a ,iolet colloidalsolution is obtain.

&u*l' F 'n*l& 'n*l0 F &u

I0. C+an#e of Sol/ent:

ulphur sis slightl$ soluble in alcohol but insoluble inwater.

saturated solution of sulphur in ethanol is when addedin water? forms a solution of sulphur.

Errors and Ommissions areexpected 3;



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Peptiation:

It is a re,erse process of coagulation.

It is a process in which a substance is

dispersed into colloidal si%e b$ anothersubstance known as pepti%ing agent e.g.gum? glue and gelatin and pepti%ed b$ waterto gi,e colloidal solution.

=reshl$ prepared =e(O:)' on treatment with asmall 6uantit$ of =e*l' solution as pepti%ing

agent forms reddish brown solution.

Errors and Ommissions areexpected 3A

P+ t i l


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P+ a rma ceu t i ca l!p p l i ca t i on o f Co l l o i d s

1. $+erapeutic!cti/ity:

Errors and Ommissions areexpected 3B

P+ t i l


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P+ t i l


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C o a t i n # :


P+ t i l


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3. Colloidal Electrolytes:

used to increase stabilit$? solubilit$ andtaste of certain compounds in a6ueous and

oil$ pharmaceutical preparation.. 'atural Colloids:

5roteins are important natural colloids andare found in bod$ as component of bone?

muscle and skin.5lasma proteins are responsible for binding

certain drugs.

Errors and Ommissions areexpected 7&

P+ a rma ce t i ca l


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;. Enymes as Colloids:

En%$mes? which are biocatal$sts? the$ are alsocolloidal in nature.


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>. (el:

"els are gelatin? pectin? cellulosederi,ati,e are used for

dermatological preparations and alsofor culture media.

colloids.pptx

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