Colloid

The solution in which size of the particles lies in  between those of true solution and suspension are called colloids or colloidal solution.

Or

Colloid is a heterogeneous mixture in which one substance is dispersed as  very fine particles in a continues medium of another substance that is dispersed medium.

  • Due to relatively smaller size of particles these mixture appears to be homogenous but actually it is heterogeneous.
  • Particles size of colloidal solution are 1-100nm.

Dispersed phase and Dispersion Medium:

The solute like constituents which has been dispersed or distributed throughout in a solvent like medium is called dispersed phase or discontinues phase.

Solvent like Medium in which the dispersed phase has been arrived or dispersed is called dispersion medium or continuous phase.

Type of colloids or colloidal solution:

Like a true solution both solute and solvent can exist in any one of the three state of matter (soli, liquid, gas)  in the same of colloidal solution also both the dispersed phase and dispersion medium  can be solid liquid or gas.

A mixture of gas can never b heterogeneous So gases cannot form colloidal solution.

Sr. No

Dispersed phase Dispersion medium      Name of colloid            Example
1. Gas Liquid Foam

Soap lather, whipped cream

2.

Gas Solid Solid Foam

Pumice stone, bread

3.

Liquid Gas Aerosol Mist, foam, cloud, spray
4. Liquid Liquid Emulsion

Milk, cod liver oil

5.

Liquid Solid Gel Jelly, butter, cheese, curd
6. Solid Gas Aerosol

Smoke, dust  storm

7.

Solid Liquid Sols Paint, starch in water
8. Solid Solid Solid sols

Alloys gems stone, rubyglass.


Colloidal solution are also called colloidal sols.

Properties of colloids :

  • Stability:

The colloidal solution are quite stable that is colloidal particles do not settle when left undistributed.

  • Visibility:

Colloidal particles are not visible by naked eyes. Some cases they are visible under ultra microscope.

  • They are heterogeneous in nature.
  • Size of particles:

The size of colloidal particles in the range 1-100nm.that is it lies in between true solution or suspension.

  • Filter ability:

Particles pass through ordinary filter paper as their particles size, is intermediate between true solution and suspension.

  • Colloidal particles carry charge:

Dispersed phase particles are suspended in dispersion medium that is they don’t settle down ,  this is because they carry charge +ve or -ve.

Example: +ve charge colloids : Fe (OH) 3,   Al (OH) 3 etc.

                   -ve charge colloids :starch, Haemoglobin etc.

  • Brownian Movement:

Such movement of  pollen grains suspended in water was first time observed by Robert Brown an English scientists in 1928 and hence is called Brownian movement.

He observed zig-zag movement of  colloidal particles. For example dust particles moving in a zig zag manner when beam of sun  light pass through them.

Brownian movement (zig zag movement of particles)

Tyndall effect:

  • The colloidal particles are big enough to scatter light passing through it.
  • As a result the path of light seen by them.
  • The scattering of beam of lightby colloidal particlesis called Tyndall effect.

Example  when a Beam of light from a torch is passed through a colloidal solution then its path becomes visible while passing through the solution. (Room must be dark).

Question Answer:

1) What is colloids?

Answer:The solution in which size of the particles lies in  between those of true solution and suspension are called colloids or colloidal solution.

2) What is Dispersed phase and dispersion medium?

Answer: The solute like constituents which has been dispersed or distributed throughout in a solvent like medium is called dispersed phase or discontinues phase.

Solvent like Medium in which the dispersed phase has been arrived or dispersed is called dispersion medium or continuous phase .

3) What is Tyndall effect?

Answer: The colloidal particles are big enough to scatter light passing through it.

  • As a result the path of light seen by them.
  • The scattering of beam of light by colloidal particles is called Tyndall effect.
  • Example when a Beam of light from a torch is passed through a colloidal solution then its path becomes visible while passing through the solution. (Room must be dark).

4) What is the Brownian movement?

Answer: Such movement of  pollen grains suspended in water was first time observed by Robert Brown an English scientists in 1928 and hence is called Brownian movement.

He observed zig-zag movement of  colloidal particles. For example dust particles moving in a zig zag manner when beam of sun  light pass through them.

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