Question

What are the characteristics of the following colloids? Give one example of each
A. Multimolecular colloids
B. Lyophobic sols
C. Emulsions

Answer 1

Hint: This question is asked from the chapter of surface chemistry. According to the definition given by IUPAC, “The colloidal state is a state of subdivision in which molecules or polymolecular particles having at least one dimension in the range of 1 nanometre and 1 micrometre, are dispersed in some medium”.

Complete step by step answer:
Let us check the characteristics of the given colloids one by one.
Multimolecular colloids are the species whose size is in the colloidal range was formed by the dissolution of smaller molecules of substance or a large number of atoms takes place. We can take an example for this as sulphur solution contains particles which have thousands of ${S_8}$.
The term ‘Lyophobic’ is formed by the combination of ‘Lyo’ and ‘phobic’ which means ‘liquid’ and ‘fearing’ respectively. So, lyophobic sols have no affinity towards the dispersion medium. Since they are liquid hating substances, it is difficult to prepare lyophobic sols. Sols of metals like silver and gold are examples for lyophobic sols.
Emulsions are an important colloid. Emulsions are two phase liquid systems consisting of two immiscible liquid phases. Here, one phase is dispersed in the other continuous phase to form an emulsion. The famous examples for emulsions are mayonnaise and milk.

Note: You should notice that the lyophobic sols are unstable and need stabilizing agents for their preservation. Hydrophobic colloids will not interact with water, this is the reason for their instability. Additional substances or emulsifiers are needed for stability. Extrinsic colloids is another name used for the lyophobic sols.