Question

Which of the following is a lyophilic colloid?
A.Sulphur sol
B. Starch
C. Gum arabica
D. Gelatin

Answer 1

The precipitation of colloids through aggregation by induction, with the addition of some suitable electrolyte is called flocculation or coagulation.

Complete answer:
The coagulation of a colloidal solution by an electrolyte does not take place unless the added electrolyte exhibits a certain minimum concentration inside the solution. The minimum concentration of the electrolyte that must be added to one litre of the sol in millimoles so that complete coagulation takes place is called the coagulation value or flocculation value of the electrolyte for the particular sol.
Different electrolytes have different coagulation values. Larger the coagulation value of the electrolyte smaller is its precipitating or coagulating power. This can be expressed as follows:
$\dfrac{\text{Coagulating power electrolyte 1}}{\text{Coagulating power electrolyte 2}}$
Some observations of Hardy and Schulze who studied about coagulation behaviour of different electrolytes include:
(i) The ions which carry the charge opposing that of sol particles are responsible for causing the coagulation of the sol. Such ions are called flocculating ions or active ions.
(ii) Coagulating power of an electrolyte is directly dependent on the fourth power of the valency of the ions which are active. This implies that greater power to cause precipitation the greater is its valency of the flocculating ion.
Water is sprinkled before sweeping the room as it helps to coagulate the dust particles. Light particles after coagulation become heavier and settle down due to which it becomes easier to remove them easily.
Colloids generally don't separate on standing. they're not separated by filtration. Suspensions are homogeneous mixtures with particles that possess diameters larger than 1000 nm or 0.00001 meter. The scale of the particles is great enough in order that they are visible to the optic.
So sulphur sol is an example of lyophobic colloid, others are examples of lyophilic colloid.

So,option (A) is the correct answer.

Note:
The lyophilic sols are relatively more stable than lyophobic sols. The stability of lyophilic sols is due to the following factors.
(1) Charge on the colloidal particles and
(ii) Solvation of colloidal particles because of greater attractive forces between dispersed phase and dispersion medium.