Colloidal State of Matter Class 12th Notes In details

Introduction:

the colloid is deriving from the Greek word "Kola" meaning glue. The main properties that differentiate colloids from suspension which can be easily prepared by directly mixing with the liquid dispersion medium.

Content We have Covered;-

✎ Definition of colloids
✎ Classification of colloids
✎ Difference between lyophilic & Lyophobic
✎ Mechanical dispersion
✎ Brigg's Arc method
✎ Peptisation
✎ Brownian movement
✎ Tyndall effect 
✎ Electrical properties
✎ Hardy-Schulze law
✎ Gold number
✎ Emulsion
✎ Types of Emulsion
✎ General application of colloids

Definition of colloids:-

The term colloid is deriving from the Greek word "Kola" meaning glue. And the term sol is openly used to represented a colloidal solution.

A colloidal solution is a heterogeneous mixture between true solution and suspension. The main properties that differentiate colloids from suspension are their uniform distribution throughout medium stability towards sitting of particles under gravity and passage of particles through the filters paper without getting the separated.

Dispersed phase(Like solute in true solution) + Dispersion medium(Like solvent in true solution)= Colloidal solution (Heterogeneous mixture).

Classification of colloids:-

(a) Dispersed phase

(b) Dispersion medium

(a) Dispersed phase:-

It is the component present in small proportion in the colloidal solution just like solid in a true solution.

(b) Dispersion medium:-

It is a component present in excess amount in the colloidal solution. Size of colloidal particle range between(1 nm to 10nm).

Difference between lyophilic & Lyophobic:-

lyophilic solution:-

✍ These are the type of solution which can be easily prepared by directly mixing with the liquid dispersion medium.

✍ These are stable and can not be precipitate easily.

✍ There is a strong affinity between the dispersed phase and dispersion medium.

✍ These are reversible nature.

✍ These are highly hydrated.

✍They don't radially undergo to coagulation by addition of an electrolyte.

✍ Gum, Starch, ink e.t.c are a common example of lyophilic colloids. 

Lyophobic Solution:-

✍ These are the type of solution which can't be easily prepared by directly mixing with a liquid dispersion medium.

✍ These are unstable and can be precipitated easily.

✍ There is no affinity between the dispersed phase and dispersion medium.

✍ These are not reversible nature. These are irreversible nature.

✍ These are not much hydrated.

✍ They readily undergo to coagulation by addition of an electrolyte.

✍ Colloidal solution of metal and metal sulphides are common examples of Lyophobic colloids.  

Mechanical dispersion:

The substance is finely powdered and then mixed with dispersion medium to form a coarse suspension. This suspension is now passed through a colloidal mill which consists of two metal disc rotating in opposite direction at a speed about 7000 revelations per minutes. This result in the breaking of suspended particles to form particles of colloidal dimensions. This method is used in the manufacture of paints, varnishes, ointments oil water colours e.t.c

Brigg's Arc method:-

This method is commonly used to prepare a colloidal solution of metals like Cu, Ag, Au, pt e.t.c

Two rods of metal to dispersed are immersed in cold water containing some Koh. Now a direct electric current is struck between the electrodes as shown in fig.

The Heat of arc evaporates the metal and vapours are condensed in water to form colloidal properties. The traces of alkali stabilize the colloidal solution.

  

Peptisation:-

Peptisation is the process of converting a precipitate into colloidal form bu shaking it with dispersion medium in the presence of the small amount of electrolyte.

The electrolyte used for this purpose is called a peptising  agent.

 Brownian movement:-

studied by Robert Brown in 1827. He observes that movement of pollen grain in water.

It is defined as the Zig-Zag movement of colloidal particles in a colloidal solution.

Cause of Brownian movement  

      

  

Colloidal particles have kinetic energy due to which they strike against the part of dispersed phase from all sides with different forces. Hence, the resultant force causes them to move. 

Tyndall effect:-

It is an optical property of a colloidal solution. This effect was first to notice by Faraday but detailed studies where made by Tyndall giving it the name Tyndall effect.

When light passing through a colloidal solution, dispersed phase particles of the colloidal solution are illuminated. The path of the ray made visible by scattering of light by the colloidal solution. 

Electrical properties:

The colloidal solution are stable because colloidal particle in sol is electrically charged due to which particle each other(one another) and don't come closer to form colloidal particle(large size) colloidal particle either carries positive charge or negative charge. 

Hardy-Schulze law:-

The main postulates

(i) The effective ions of electrolyte in bringing about coagulation are those which carry opposite charge to that of colloidal particle.

(ii) Greater is the valency of coagulating ions then greater is it's coagulating power to bring about coagulation.

Gold number:-

This term was used by Zsigmondy in 1901. It is defined as the amount of lyophilic colloid(in mg) which must be added to 10ml of the standard red gold solution so that no coagulation takes place. (Red-Blue).

When 1ml of 10% NaCl is quickly added to it.   

 Emulsion:-

An Emulsion is a colloidal dispersion in which both dispersed phase and dispersion medium are liquid. Eg:- Milk

Types of Emulsion:-

(i) Oil in water(O/W)

(ii) Water in Oil(W/O)

(i) Oil in water(O/W):-

The type of emulsion in which oil is dispersed phase and water is dispersion medium. Eg:- Milk, Vanishing cream

(ii) Water in Oil(W/O):-

The type of emulsion in which water is dispersed phase and oil is dispersion medium. Eg:- Butter, cold creams

Method of preparation of Emulsion:-

When two liquids are strongly shaken and passed through colloidal mill called Homogenizer. The emulsion formed are not much stable and two liquid separate outstanding.

General application of colloids:-

(i) In medicine

(ii) Swage treatment

(iii) purification of water

(iv) cleaning action of soap

(i) In medicine:-

Medicine in the colloidal form is easily absorbed by body tissue. Hence more effective.

(ii) Swage treatment:-

When swage water having a dart, mud e.t.c are passed through plates(changed) feet at high potential. Colloidal particles are coagulated by electrophoresis.

(iii) purification of water:-

Colloidal particles in water can be precipitated by adding Alum(Al3+).

Hence it can neutralize the negative charged colloidal particles.

(iv) cleaning action of soap:-

Soap solution can be considered colloidal in nature. It removes diet either by adsorption or by emulsifying the greasy matter sticking on cloth.

Also Read: the solid-state class 12th imperfection of metals 

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