--%>
Assignment Help - homework help

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 solid in liquid solutions. The

    The French chemist Francois Marie Raoult (1886) carried out a series of experiments to study the vapour pressure of a number of binary solutions. On the basis of the results of the experiments, he proposed a generalization called Raoult's law which states that, <

    		•
  • Q : Cons of eating organic foods Illustrate

    Illustrate the cons of eating organic foods?

    		•
  • Q : Basic concept Give me answer of this

    Give me answer of this question. The volume of water to be added to 100cm3 of 0.5 N N H2SO4 to get decinormal concentration is : (a) 400 cm3 (b) 500cm3 (c) 450cm3 (d)100cm3

    		•
  • Q : Molecular energies and speeds The

    The average translational kinetic energies and speeds of the molecules of a gas can be calculated.The result that the kinetic energy of 1 mol of the molecules of a gas is equal to 3/2 RT can be used to obtain numerical values for the

    		•
  • Q : What is solvent dielectric effect?

    Ionic dissociation depends on the dielectric constant of the solvent.The Arrhenius that ions are in aqueous solutions in equilibrium with parent molecular species allows many of the properties of ionic solutions to be understood. But difficulties began to

    		•
  • Q : Define Bond Energies - Bond Charges

    Energy changes in some chemical reactions can be used to deduce the energies of chemical bonds. Our understanding of the molecular basis of thermodynamic properties is extended when we ask why the enthalpy change for a reaction is what it is. We deduce,

    		•
  • Q : Finding Molarity of final mixture Can

    Can someone help me in finding out the right answer. 25ml of 3.0 MHNO3 are mixed with 75ml of 4.0 MHNO3. If the volumes are adding up the molarnity of the final mixture would be: (a) 3.25M (b) 4.0M (c) 3.75M (d) 3.50M

    		•
  • Q : What are lattices and unit cells? The

    The repeating, atomic level structure of a crystal can be represented by a lattice and by the repeating unit of the lattice, the unit cell.It was apparent very early in the study of crystals that the shapes of crystals stem from an ordered array of smaller

    		•
  • Q : Question related to colligative

    The colligative properties of a solution depend on: (a) Nature of solute particles present in it (b) Nature of solvent used (c) Number of solute particles present in it (d) Number of moles of solvent only

    		•
  • Q : Strength of Nacl in solution To 5.85gm

    To 5.85gm of Nacl one kg of water is added to prepare of solution. What is the strength of Nacl in this solution (mol. wt. of nacl = 58.5)? (a) 0.1 Normal (b) 0.1 Molal (c) 0.1 Molar (d) 0.1 FormalAnswer:

    		•