Colloids: Coagulation, Protection and Application of Lyophilic Sols (For CBSE, ICSE, IAS, NET, NRA 2022)

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Coagulation of Lyophilic Sols

The stability of lyophilic sols are due to the charge and solvation of the colloidal particles.

On this basis, These are the ways to coagulate the lyophilic sol:

  • By adding an electrolyte and
  • By adding a suitable solvent.

By doing these a lyophilic sol is coagulated.

Protection of Colloids

  • When a lyophilic sol is added to the lyophobic sol, the lyophilic particles form a layer around lyophobic particles and thus protect the latter from electrolytes.
  • Due to this unique property of Lyophilic colloids, they are called protective colloids.

Application of Colloidal Solution

Sewage Disposal

  • Colloidal particles of dirt, etc. carry electric charge.
  • When sewage is allowed to pass through metallic plates kept at a high potential, the colloidal particles move to the oppositely charged electrode and get precipitated. Therefore, sewage water is purified.

Purification of Water in the Well

When alum is added to muddy water, the negatively charged particles of the colloid are neutralized by ions. Hence the mud particles settle down and the water be filtered and puried.

Smoke Precipitation

  • Smoke particles are electrically charged colloidal particles of carbon in air.
  • Smoke from chimneys is allowed to pass through a chamber having a number of metallic plates connected to a source of high potential. This arrangement is called a Cottrell՚s Precipitator (Fig) .
Smoke Precipitation

Charge particles of smoke get attracted to the oppositively charged electrode and get precipitated and hot purified air passes out.


A colloidal solution of silver bromide in gelatin is applied on glass plates or celluloid films to form photo-sensitive plates in photography.

Clotting of Blood

  • Blood is a colloidal solution and is negatively charged.
  • If we apply a solution of on bleeding, then it stops and clotting of the colloidal particles of blood takes place.

Rubber Plating

  • Latex is a colloidal solution of negatively charged rubber particles
  • The object to be rubber plated is made the anode in the rubber plating bath. The negatively charged rubber particles move towards the anode and get deposited on it.

Blue Colour of Sky

  • The colloidal dust particles floating about in the sky scatter the blue light, that makes the sky appear blue.
  • In the absence of colloidal particles, the sky would have appeared dark throughout.


Emulsions are colloidal solutions in which both the dispersed phase and dispersed medium are liquids.

There are following types of emulsion:

Oil- In- Water Emulsion

  • The dispersed phase is oil while the dispersion medium is water.
  • Milk is an example of this type.

Water-In-Oil Emulsion

  • Dispersed phase is water and dispersion medium is oil.
  • Butter, cod- liver oil, cold creams are examples of this type.


  • The liquids forming emulsion i.e.. oil and water will separate out on keeping they are immiscible.
  • Therefore, an emulsifying agent or emulsifier is added to stabilize the emulsion.
  • Soap is a common emulsifier.
  • The preparation of emulsion in the presence of an emulsifier is called emulsification.

Application of Emulsion

  • The cleansing action of soap and synthetic detergents for washing clothes is based on upon the formation of oil in water emulsion.
  • Milk is an emulsion of fat in water.
  • Various cold creams, vanishing creams, body lotions etc. are all emulsions.
  • The digestion of fats in the intestine occurs by the process of emulsification.
  • Emulsions are used for concentrating the Sulphide ores by froth flotation process.


  • Gels are the type of colloids in which the dispersed phase is a liquid and the dispersion medium is a solid.
  • Cheese, jelly, boot polish are common examples of gel.
  • Gels may shrink on keeping by losing some of the liquid held by them. This is known as syneresis or resetting on standing.
  • Gels are divided in two categories elastic gels and non-elastic gels.
  • Elastic gels are reversible. When partly dehydrated on loosing water, they change back into the original form.
  • Non elastic gels are not reversible.

Nano Particles

  • A material containing particles with dimension in the size range 1 nm – 100 nm in at least one direction is termed as nano material.
  • The beautiful ruby red colour of some types of glass is due to the presence of nano particle of gold in it.

Nano materials fall in two categories:

  • Fullerenes
  • Inorganic nano material


Fullerenes are allotropes of carbon which are hollow carbon spheres consisting of large number of carbon atoms bonded chemically like .

Inorganic Nano Material

Inorganic nano particles are made of metals, semiconductors or oxides with peculiar electrical, mechanical, optical or chemical properties.

Application of Nano Material

  • They are used for making miniature batteries, super absorbents, extremely tiny electronic devices, parts of automobiles and as packaging films.
  • Nano capsules and nanodevices present new possibilities for drug delivery, gene therapy, and medical diagnostics.
  • Due to their large surface area, nanoparticles made of transition element oxides exhibit catalytic properties.

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