Question

What is peptization? Give examples.

Answer 1

Hint:It is generally used in colloidal chemistry. It is of great importance for changing precipitates into colloids and hence forming a colloidal mixture.

Complete step by step answer:
Peptization is also known as Deflocculation. It is a process which is responsible for the formation of colloids by breaking up of precipitate using an electrolyte.
We can use an example of clay, which will normally form a precipitate if added to water but if we use sodium carbonate, it will act as a peptizing agent and hence allowing clay to form a colloid with water.
Now we will discuss the cause of peptization – if we add an electrolyte to a freshly precipitated solution, the precipitate particles will adsorb on either the positive ion part or the negative ion part of the electrolyte. Due to this, the electrostatic repulsion force between the colloidal particles acts and the particle breaks and forms a colloidal mixture.
Generally, an electrolyte is considered as a peptizing agent.
When the colloidal particles bear the same sign, due to the repulsion force acting between them they cannot bind together.
Example- Freshly precipitated aluminium hydroxide is very difficult to filter through a filter paper due to its fine particle size. The minute particles pass through the filter paper. To solve this problem, we can peptize this solution by addition of a concentrated salt.
Peptization is also used in synthesis of nanoparticles to split large groups of particles into several smaller groups. This is done by adding a surfactant or by changing the surface properties.

Note: We should not assume from its name that peptizing agents have something to do with the formation of peptide linkage or making any other structural change to the original molecules. It just adsorbs on the surface of the precipitates and breaks the electrical repulsion between the precipitate molecules hence allowing them to form a colloidal solution.