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 : Moles of HCl present in .70 L of a .33

    Detail the moles of HCl which are present in .70 L of a .33 M HCl solution?

  • Q : Mole fraction of solute The mole

    The mole fraction of the solute in 1 molal aqueous solution is: (a) 0.027 (b) 0.036 (c) 0.018 (d) 0.009
    What is the correct answer.

  • 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 : Normality of solution containing

    Can someone please help me in getting through this problem. Determine the normality of a solution having 4.9 gm H3PO4 dissolved in 500 ml water: (a) 0.3  (b) 1.0  (c) 3.0   (d) 0.1

  • Q : Concentration of Sodium chloride

    Provide solution of this question. If 25 ml of 0.25 M NaCl solution is diluted with water to a volume of 500ml the new concentration of the solution is : (a) 0.167 M (b) 0.0125 M (c) 0.833 M (d) 0.0167 M

  • Q : What do you mean by the term Organic

    What do you mean by the term Organic Chemistry? Briefly define the term?

  • Q : Eutectic Formation In some two

    In some two component, solid liquid systems, a eutectic mixture forms.

    Consider, now a two component system at some fixed pressure, where the temperature range treated is such as to include formation of one or more solid phases. A simple behavior is shown b

  • Q : Solubility are halides are halogens

    are halides are halogens more soluble? why?

  • Q : Avogadros hypothesis how avogadros

    how avogadros hypothesis used to deduce the atomicity of elementry gases ?

  • Q : Describe Thermodynamics Properties The

    The free energy property leads to convenient expressions for the volume and pressure dependence of internal energy, enthalpy and the heat capacities.

    All the properties of a chemical system, a sample of a substance, or a mixture of substances have some fixe

2015 ©TutorsGlobe All rights reserved. TutorsGlobe Rated 4.8/5 based on 34139 reviews.