Question

Peptization is a:
(a) Process of converting a colloidal solution into precipitate
(b) Process of converting precipitate into colloidal solution
(c) Process of converting soluble particles to form colloidal solution
(d) Process of bringing colloidal molecule into solution

Answer 1

The end result of peptization is the formation of a colloidal solution. It starts from the compounds which were unable to get dissolved in the solution.

Complete Solution :
- Understanding the process of peptization is crucial to answer this question. We explain it as follows.
Peptization is the process in which a freshly prepared precipitate converts into a colloidal solution in the dispersion medium when it is mixed with a suitable electrolyte. The colloidal solution formed is stable, meaning it does not settle down with time.
- The mechanism of this process is quite simple. The precipitate which is freshly prepared contains particles which are bigger than the required size by the dispersion medium to form a solution or colloid. Hence, it settles down forming insoluble substance at the bottom of the container. As we know, these particles always have an electrical double layer. The first layer consists of charged species which are tightly adsorbed onto the surface of the particle while the second layer which is also known as the diffused layer, consists of charged species which are loosely held by the first layer.
- When we add an electrolyte that will dissociate into charged species having an opposite charge to the diffused layer, then the second layer will get neutralised. This exposes the first layer of charged species. As all the particles in the dispersion medium have the same charge on the first layer, they now repel each other and therefore are unable to settle. This forms a colloidal solution from a precipitate.
So, the correct answer is “Option B”.

Note: A colloidal solution only forms from a precipitate when the electrolyte is added in carefully calculated amounts and has the charge opposite to that of the second layer on the precipitate particles.
- It should also be clear that not all precipitates can be converted into colloidal solutions because the prerequisite is a high surface area to the volume ratio.