Disperse systems. Colloidal solutions:

the preparation, purification and

properties.

THEME

PlanPlan•Disperse systems. Classification.Disperse systems. Classification.•Colloidal stat. Types of colloidal Colloidal stat. Types of colloidal

solution. solution. •Preparation of colloidal solutions.Preparation of colloidal solutions.•Method of purification colloidal solution.Method of purification colloidal solution.•Structure of colloidal parts.Structure of colloidal parts.•Stability of disperse systemsStability of disperse systems•Coagulation. The coagulation threshold.Coagulation. The coagulation threshold.•Sedimentation.Sedimentation.

Disperse systems Disperse systems are called are called systems, which consist of two systems, which consist of two phases, one of which is phases, one of which is scattered or dispersed in other.scattered or dispersed in other.

The disperse phaseThe disperse phase -- phase phase which is scattered (dispersed) which is scattered (dispersed) in mediumin medium..

The disperse medium -The disperse medium - phase phase in which dispersion donein which dispersion done. .

Classification:Classification:• By stat of dispersed phase and

dispersed medium

• By size of dispersed phase

FogFog

Colloidal solutionColloidal solution

Colloidal solutions have Colloidal solutions have dispersed phase particle, dispersed phase particle, which size between 10which size between 10-9-9 to to 1010-7-7m or 1 nm to 100 nm.m or 1 nm to 100 nm.

Classification of Classification of colloidal solutioncolloidal solution

•Lyophilic colloidsLyophilic colloids - solvent-attracting - solvent-attracting

•Lyophobic colloids - Lyophobic colloids - solvent-solvent-repellingrepelling

Preparation of Preparation of colloidal solutionscolloidal solutions

1. Dispersion or disintegration methods:• Mechanical disintegration • Electro-disintegration (Bredig s method). 2. Peptization 3. Condensation or aggregation

methods:• chemical reaction: - double decomposition; - reduction; - oxidation; - hydrolysis.• exchange of solvent;• condensing vapours of a substance into the

solvent;• excessive cooling.

Dispersion

These methods involve the breaking of the bigger particles to colloidal size.

Mechanical Mechanical disintegrationdisintegration

• The The mechanical disintegrationmechanical disintegration is carried out is carried out in a machine called in a machine called ««colloid millcolloid mill»». It consists . It consists of two steel discs with a little gap in between of two steel discs with a little gap in between and capable of rotating in the opposite and capable of rotating in the opposite directions at high speed. А suspension of the directions at high speed. А suspension of the substance in water introduced into the mill. substance in water introduced into the mill. The size of suspension particles is reduced to The size of suspension particles is reduced to that of colloidal sizethat of colloidal size

Electro-disintegration Electro-disintegration (Bredig(Bredig’’s method)s method)

This method is employed for obtaining This method is employed for obtaining colloidal solutions of metals like gold, colloidal solutions of metals like gold, silver, platinum etc. An electric arc is silver, platinum etc. An electric arc is set up between two metallic set up between two metallic electrodes suspended in а trough of electrodes suspended in а trough of water. The intense heat of the arc water. The intense heat of the arc converts the metal into vapours converts the metal into vapours which are condensed immediately in which are condensed immediately in the ice cold water bath resulting in the ice cold water bath resulting in the formation of particles of colloidal the formation of particles of colloidal sizesize

PeptizationPeptization - is a - is a process of passing of a process of passing of a precipitate into colloidal precipitate into colloidal particles on adding particles on adding suitable electrolyte. The suitable electrolyte. The electrolyte added is called electrolyte added is called peptizing agent. peptizing agent.

Condensation or Condensation or aggregation methodsaggregation methods

These methods involve the These methods involve the joining together of а large joining together of а large number of smaller particles to number of smaller particles to form particles of colloidal size. form particles of colloidal size.

ChemicalChemical reactionsreactionsBy double decomposition:

AsAs22OO33 + 3H + 3H22S = AsS = As22SS33 + 3H + 3H22OO By reduction:

2 AuCl3 + 3SnCl2=2 Аu + 3SnCl4 By oxidation:

BrBr22 + H + H22S = S + 2 HBrS = S + 2 HBr By hydrolysis:

FeClFeCl33 + + 33 HH22OO = = FeFe((OHOH))33 + + 33 HClHCl

By exchange of By exchange of solventsolvent

Substances like sulphur and Substances like sulphur and phosphorous are fairly phosphorous are fairly soluble in alcohol but less soluble in alcohol but less soluble in water. If their soluble in water. If their alcoholic solutions are alcoholic solutions are poured in water, colloidal poured in water, colloidal solutions of sulphur and solutions of sulphur and phosphorus are obtainedphosphorus are obtained

By condensing vapours of а By condensing vapours of а substance into the solventsubstance into the solvent

•Colloidal solutions of sulphur and Colloidal solutions of sulphur and mercury in water are prepared by mercury in water are prepared by passing their vapours cold water passing their vapours cold water containing а little stabilizing containing а little stabilizing agent like ammonium nitrate.agent like ammonium nitrate.

By excessive By excessive coolingcooling

Colloidal solution of ice Colloidal solution of ice in an organic solvent in an organic solvent like ether is obtained by like ether is obtained by freezing a mixture of freezing a mixture of the solvent and waterthe solvent and water

Purification colloidal Purification colloidal solutionssolutions

When a colloidal solution is When a colloidal solution is prepared, quite often it contains prepared, quite often it contains certain impurities of electrolytes certain impurities of electrolytes which are crystalloidal in nature which are crystalloidal in nature and tend to destabilize the and tend to destabilize the solution. Hence their removal is solution. Hence their removal is very essential. very essential.

Method of purification Method of purification colloidal solutioncolloidal solution

•Dialysis: electrodialysis; Dialysis: electrodialysis; compensatory dialysis; compensatory dialysis; vividialisis; hemodialysis; vividialisis; hemodialysis; Artificial kidney.Artificial kidney.

•UltrafiltrationUltrafiltration

•UltracentrifugationUltracentrifugation

DialysisDialysis• The process of separating the The process of separating the

particles of colloids from those of particles of colloids from those of crystalloids by diffusion of the crystalloids by diffusion of the mixture through semipermeable mixture through semipermeable membrane (а parchment or an animal membrane (а parchment or an animal membrane) is known as dialysis.membrane) is known as dialysis.

• The above process can be quickened The above process can be quickened if an electric field is applied around if an electric field is applied around the membrane (the process is then the membrane (the process is then called Electro- dialysis). called Electro- dialysis).

Electro-dialyserElectro-dialyser

The most important application The most important application of dialysis is in the purification of dialysis is in the purification of blood in the of blood in the artificial artificial kidneykidney

• artificial kidneyartificial kidney

Structure of colloidal Structure of colloidal partsparts

{[nuclear] + adsorptive layer} diffuse laeyr{[nuclear] + adsorptive layer} diffuse laeyr

• Structure of a micelle Fe (OH)Structure of a micelle Fe (OH)33..

• The iron hydroxyde sol a formed, if iron The iron hydroxyde sol a formed, if iron chlorate is hydrolyzed: chlorate is hydrolyzed:

• FeClFeCl33 + H + H22O = Fe(OH)O = Fe(OH)33 + HCl + HCl

• Reaction products interact:Reaction products interact:

• Fe (OH)Fe (OH)33 + HC1 = FeOCI + 2H + HC1 = FeOCI + 2H22O O

• Iron oxychloride can dissocied:Iron oxychloride can dissocied:

• FeOCI = FeOFeOCI = FeO++ + Cl + Cl--

• The potential-determining ionsThe potential-determining ions will be only will be only FeOFeO++ as the ion Cl as the ion Cl--::

• {[Fe(OH){[Fe(OH)33]]mm n FeO n FeO++ (n-x)Cl (n-x)Cl--}}x+x+ xCl xCl--

PropertiesProperties1. 1. Physical Properties Physical Properties

• Heterogeneous characterHeterogeneous character• StabilityStability• FilterabilityFilterability • VisibilityVisibility 2. Colligative properties - osmotic pressure2. Colligative properties - osmotic pressure3. Mechanical properties – Brownian 3. Mechanical properties – Brownian

movementmovement 4. Optical properties – Tyndall affect4. Optical properties – Tyndall affect 5. Electrical properties5. Electrical properties

Kinetic stabilityKinetic stability

• АА major source of kinetic stability of major source of kinetic stability of colloids is the existence of an electric colloids is the existence of an electric charge on the surfaces of the particles. charge on the surfaces of the particles. On the account of this charge, ions of On the account of this charge, ions of opposite charge tend to cluster nearby, opposite charge tend to cluster nearby, and an ionic atmosphere is formed.and an ionic atmosphere is formed.

On placing а colloidal solution under the On placing а colloidal solution under the influence of an electric field, the particles of influence of an electric field, the particles of the dispersion medium move towards the dispersion medium move towards oppositely charged electrode, provided the oppositely charged electrode, provided the colloidal particles is called electro-osmosis. colloidal particles is called electro-osmosis.

The movement of colloidal particles The movement of colloidal particles under the influence of an electric field is under the influence of an electric field is

called called electrophoresiselectrophoresis or cataphoresis. or cataphoresis.

а)а) Before Before electrophoresis electrophoresis

(b)(b) After After electrophoresis electrophoresis

Flocculation Flocculation (coagulation)(coagulation)

Aggregation of the Aggregation of the particles arising from the particles arising from the stabilizing effect of this stabilizing effect of this secondary minimum is secondary minimum is called called flocculationflocculation. .

Hardy-Schulze Hardy-Schulze LawLaw

•Greater is the valency of the Greater is the valency of the oppositely charged ion of the oppositely charged ion of the electrolyte being added, the electrolyte being added, the faster is the coagulation.faster is the coagulation.

SedimentationSedimentation

•In In аа gravitational field, heavy gravitational field, heavy particles settle towards the particles settle towards the foot of foot of аа column of solution column of solution by the process called by the process called sedimentation. sedimentation.