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 : Concentration factor affected by

    Can someone please help me in getting through this problem. Which of the given concentration factor is affected by the change in temperature: (1) Molarity (2) Molality (3) Mole fraction (4) Weight fraction

  • Q : Calculating density of water using

    What is the percent error in calculating the density of water using the ideal gas law for the following conditions:  a. 110 oC, 1 bar   b. 210 oC 10 bar  c. 374 o

  • Q : Organic and inorganic substances living

    living beings are made up of organic and inorganic substances.according to their complexity of their molecules how can ach of these substances be classified?

  • Q : Explain the process of adsorption of

    The extent of adsorption of a gas on a solid adsorbent is affected by the following factors: 1. Nature of the gas Since physical adsorption is non-specific in nature, every gas will get adsorbed on the

  • Q : Nuclear Magnetic Resonance The nuclear

    The nuclear states produced by a magnetic field are studied in nuclear magnetic resonance spectroscopy.The frequency of the radiation that corresponds to the nuclear magnetic energy level spacings and the weakness of the radiation absorption that must be e

  • Q : Biodegradable polymers what are the

    what are the examples of biodegradable polymers

  • Q : Problem on endothermic or exothermic At

    At low temperatures, mixtures of water and methane can form a hydrate (i.e. a solid containing trapped methane). Hydrates are potentially a very large source of underground trapped methane in the pole regions but are a nuisance when they form in pipelines and block th

  • Q : Molarity of the final mixture Can

    Can someone please help me in getting through this problem. Two solutions of a substance (that is, non electrolyte) are mixed in the given manner 480 ml of 1.5M first solution + 520 ml of 1.2M second solution. Determine the molarity of the final mixture

  • Q : Vapour pressure of volatile substance

    Provide solution of this question. According to Raoult's law the relative lowering of vapour pressure of a solution of volatile substance is equal to: (a) Mole fraction of the solvent (b) Mole fraction of the solute (c) Weight percentage of a solute (d) Weight perc

  • Q : Examples of reversible reaction

    Describe some examples of a reversible reaction?

©TutorsGlobe All rights reserved 2022-2023.