1. Presentation On Colloids Topics:- 1. Purification of Sols 2. Electrical properties of Sols Presented by:- Shabbir, Jakaria, Rashed, Parvez, Tanvir, Hasan

2. Purification of Sols Purification :- The process of removing impurities.Purification :- The process of removing impurities. Sols :- Sols are colloidal systems in which a solid is dispersed in a liquid medium.Sols :- Sols are colloidal systems in which a solid is dispersed in a liquid medium. e.g. Blood and paint etc. e.g. Blood and paint etc. There are three processes to purify sols- 1.Dialysis 2.Electodialysis 3.Ultrafiltration 1.Dialysis 2.Electodialysis 3.Ultrafiltration

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

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

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

6. 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.

7. Electrical double layer: Let us consider, the surface of colloidal particle acquires a positive (+ ve) charge by adsorption. The positive ions attract the negative ion from the medium and from a compact layer. The medium form a diffuse layer. The combination of the compact and diffuse layer is referred to as stern/electrical double layer.

8. Electrophoresis: The movement of sol particles under an applied electric potential is called electrophoresis. If the electric potential is applied across two platinum electrodes dipping in a hydrophilic sol, the dispersed particles move toward one or the other electrode If the sol particle migrates toward the positive electrode, they carry a negative charge and vice versa. By noting the direction of movement of the sol particle, we can determine whether they carry a positive or negative charge.

9. Coagulation or Precipitation: The flocculation and settling down of the discharged sol particles is called coagulation or precipitation. --How can coagulation be caused? The coagulation of a given sol is achieved by 4 ways. 1.By addition of electrolytes 2.By electrophoresis 3.By mixing two oppositely charged sols 4.By boiling