PresentationPresentationOnOn

ColloidsColloids

Topics:- Topics:-

1. Purification of Sols1. Purification of Sols

2. Electrical properties of 2. Electrical properties of Sols Sols

Presented by:-Presented by:-

Shabbir, Jakaria, Rashed, Shabbir, Jakaria, Rashed, Parvez, Tanvir, HasanParvez, Tanvir, Hasan

Purification of SolsPurification of Sols

• Purification :-Purification :- The process of removing The process of removing impurities.impurities.

• Sols :-Sols :- Sols are colloidal systems in Sols are colloidal systems in which a solid is dispersed in a liquid which a solid is dispersed in a liquid medium.medium.

e.g. Blood and paint etc.e.g. Blood and paint etc.

There are three processes to purify sols-There are three processes to purify sols-

1.Dialysis 2.Electodialysis 1.Dialysis 2.Electodialysis 3.Ultrafiltration3.Ultrafiltration

DialysisDialysis

• The process of removing ions from a sol by The process of removing ions from a sol by diffusion through a permeable membrane is diffusion through a permeable membrane is called dialysis.called dialysis.

A sol containing dissolved ions A sol containing dissolved ions (electrolyte) or molecules is placed in a bag of (electrolyte) or molecules is placed in a bag of permeable membrane dipping in pure water, the permeable membrane dipping in pure water, the ions diffuse through the membrane. By using a ions diffuse through the membrane. By using a continuous flow of fresh water, the concentration continuous flow of fresh water, the concentration of the electrolyte outside the membrane tends to of the electrolyte outside the membrane tends to be zero. Thus diffusion of the ions into pure be zero. Thus diffusion of the ions into pure water remains brisk all the time. In this way, water remains brisk all the time. In this way, practically all the electrolyte present in the sol practically all the electrolyte present in the sol can be removed easily. can be removed easily.

Electro dialysisElectro dialysis

• Electro dialysis is a membrane Electro dialysis is a membrane process during which ions are process during which ions are transported through semipermeable transported through semipermeable membrane, under the influence of an membrane, under the influence of an electric potential.electric potential.

Ultra filtrationUltra filtration

• The separation of solid particles The separation of solid particles from the liquid medium and from the liquid medium and electrolytes by flirtation through electrolytes by flirtation through and ultra filter is called ultra and ultra filter is called ultra filtration.filtration.

Electrical properties of sol:The sol particles carry an electric

charge: The suspended particles in colloidal dispersion posses either positive or

negative charges. The mutual forces of repulsion between similarly charged

particles prevent them from aggregating and give stability to sols. The sol

particles acquire positive or negative charge by preferential adsorption

medium.

Electrical double layer: Electrical double layer: Let us consider , the surface of Let us consider , the surface of

colloidal particle acquires a positive colloidal particle acquires a positive (+ ve) charge by adsorption. The (+ ve) charge by adsorption. The

positive ions attract the negative ion positive ions attract the negative ion from the medium and from a from the medium and from a

compact layer. The medium form a compact layer. The medium form a diffuse layer. The combination of the diffuse layer. The combination of the compact and diffuse layer is referred compact and diffuse layer is referred

to as stern/electrical double layer.to as stern/electrical double layer.

Electrophoresis: Electrophoresis: The movement of sol particles under an The movement of sol particles under an

applied electric potential is called applied electric potential is called electrophoresiselectrophoresis..

If the electric potential is applied across If the electric potential is applied across two platinum electrodes dipping in a two platinum electrodes dipping in a

hydrophilic sol, the dispersed particles hydrophilic sol, the dispersed particles move toward one or the other electrodemove toward one or the other electrode

If the sol particle migrates If the sol particle migrates toward the positive electrode, they carry toward the positive electrode, they carry

a negative charge and vice versa.a negative charge and vice versa. By noting the direction of By noting the direction of

movement of the sol particle, we can movement of the sol particle, we can determine whether they carry a positive determine whether they carry a positive

or negative charge.or negative charge.

Coagulation or PrecipitationCoagulation or Precipitation:: The flocculation and settling down of the The flocculation and settling down of the

discharged sol particles is called discharged sol particles is called coagulation or precipitationcoagulation or precipitation..

--How can coagulation be caused? --How can coagulation be caused?

The coagulation of a given sol is The coagulation of a given sol is achieved by 4 waysachieved by 4 ways..

1.By addition of electrolytes1.By addition of electrolytes2.By electrophoresis2.By electrophoresis

3.By mixing two oppositely charged sols3.By mixing two oppositely charged sols4.By boiling4.By boiling