Question

Define coagulating value of solution?

Answer 1

Hint: As we know, coagulation means precipitation or aggregation of particles. Therefore, coagulation value will be related to the phenomenon leading to aggregation of its particles.

Complete step by step answer:
The precipitation of colloidal solution through induced aggregation by the addition of suitable electrolyte is known as coagulation. Also, coagulation of a colloidal solution by an electrolyte does not take place until the added electrolyte has certain minimum concentration in the solution. The minimum concentration of an electrolyte which is required to cause coagulation is known as coagulating value of sol. It is usually expressed in terms of milli-moles per litre.
Coagulation power is inversely proportional to coagulation value.
There are many techniques of coagulation. Some of them are as given below –

Boiling:
On boiling a sol, the molecules of the dispersion medium start colliding with each other and which further disturbs the adsorption layer. This reduces the charge on the sol. This leads to the settling of the particles.
Mixing two oppositely charged sols:
In this type of coagulation equal amounts of oppositely charged particles are mixed, which cancel out their charges. This leads to coagulation.

Electrophoresis:
In this type of coagulation, the particles of the dispersed phase move towards an oppositely charged electrode, which then gets neutralized. This leads to coagulation.

Prolonged dialysis:
As we know, the stability of a colloidal sol is due to the presence of a small amount of electrolyte on prolonged dialysis electrolyte. This is completely removed. And therefore, sol gets coagulated.
Therefore, the answer is –
“The minimum concentration of electrolyte in millimoles required to cause coagulation of one litre of colloidal solution is called coagulation value”.

Additional Information: Coagulation is also known as flocculation or precipitation.

Note: Gold Number is the minimum mass of protective colloid which is added to 10 ml of a standard red gold sol (Containing 0.0053 to 0.0058) so that no coagulation of the gold sol occurs.