Explain the process of coagulation of colloidal solutions.

Presence of small concentrations of appropriate electrolyte is necessary to stabilize the colloidal solutions. However, if the electrolytes are present in higher concentration, then the ions of the electrolyte neutralize the charge on the colloidal particles may unite together to form bigger particles which are then precipitated. The precipitation of a colloid through induced aggregation by the addition of some suitable aggregation by the addition of some suitable electrolyte is called coagulation or flocculation.

The coagulation of a colloidal solution by an electrolyte does not tales place until the added electrolyte has certain minimum concentration in the solution. The minimum concentration of the electrolyte in millimoles that must be added to one litre of the sol so as to bring about complete coagulation value of the electrolyte for the sol.

Different electrolytes have dissimilar coagulation values. Smaller the coagulation value of the electrolyte larger is its coagulating or precipitating power. This can be expressed as under.
2021_Collidal solution.png 

The coagulation behaviour of various electrolytes was studied in details by Hardy and Schulze. They experience that:
The ions carrying charges opposite to that of sol particles are effective in causing the coagulation of the sol. such ions are called flocculating ions or active ions.
Coagulating power of an electrolyte is directly proportional to the fourth power of the valency of the active ions. This implies that greater the valency of the flocculating ion greater is the power to cause precipitation.

Thus, for the coagulation of sols carrying negative charge (like As2S3 sol), Al3+ ions are more effective then Ba2+ or Na+ ions. Similarly, for the coagulation of sols carrying positive charge, such as Fe(OH)3 sol PO43- ions are more effective than SO42- or Cl- ions. The two observations given above are collectively called Hardy Schulze rule.

Coagulation of colloidal solutions can also be attained by the subsequent techniques:
By mutual precipitations: when two oppositely charged sols such as Fe(OH)3 and As2S3 are mixed and equimolar properties, they neutralize each other and may get coagulated. Sometimes the sols may get coagulated due to the mutual destruction of stabilizing agents.
By electrophoresis: we know that during electrophoresis the sol particles move towards the oppositely charged electrodes. If the process is carried for a long time, the particles will touch the electrode, lose their charge and get coagulated.
By repeated dialysis: the stability of colloidal is due to the presence of a small amount of electrolyte. Of the electrolyte is completely removed by repeated dialysis, the sol will get coagulated.
By heating: the sol may be coagulated even by simple heating.

   Related Questions in Chemistry

  • Q : Explain alcohols and phenols in organic

    Alcohols and phenols are the compounds

  • Q : Molecular Structure type The ionic

    The ionic radii of Rb+ and I- respectively are 1.46 Å and 2.16Å. The very most probable type of structure exhibited by it is: (a) CsCl type  (b) ZnS type  (c) Nacl type  (d) CaF2 type

    Q : Q what is the basicity of primary

    what is the basicity of primary secondary and tertiary amines in chlorobenzene

  • Q : Dipole moment Elaborate a dipole moment

    Elaborate a dipole moment?

  • Q : Concentration of urea Help me to go

    Help me to go through this problem. 6.02x 1020 molecules of urea are present in 100 ml of its solution. The concentration of urea solution is: (a) 0.02 M (b) 0.01 M (c) 0.001 M (d) 0.1 M (Avogadro constant, N4= 6.02x 1023mol -1)<

  • Q : Describe physical adsorption and its

    When the forces of attraction existing between adsorbate and adsorbent are van der Waal's forces, the adsorption is called physical adsorption. This type of adsorption is also known as physisorption or van der Waal's adsorption. Since the forces existing between adsorbent and adsorbate are very w

  • Q : Solubility of a gas The solubility of a

    The solubility of a gas in water depends on: (a) Nature of the gas (b) Temperature (c) Pressure of the gas (d) All of the above.

    Can someone help me in finding out the right answer.

  • Q : Difference in Mendeleevs table and

    Briefly describe the difference in the Mendeleev’s table and modern periodic table?

  • Q : Structure of a DNA molecule Elaborate

    Elaborate the structure of a DNA molecule?

  • Q : Thermodynamics 1 Lab Report I already

    I already did Materials and Methods section. I uploaded it with the instructions. Also, make sure to see Concept Questions and Thinking Ahead in the instructions that I uploaded. deadline is tomorow at 8 am here is the link to download all instructions because I couldn't attach all of t