Question

Name the lyophobic colloid present in the milk.

Answer 1

Hint: A mixture in which one substance is made up of microscopically dispersed insoluble particles which are suspended throughout another substance is defined as a colloid. Generally, it is believed that the particles must be dispersed in a liquid medium, however others extend the definition to include substances like aerosols and gels.

Complete solution:
The colloids are categorized into two types on the basis of the nature of the interaction between the dispersion phase and the dispersed medium: lyophilic and lyophobic colloids.
Lyophilic colloid –
It is described as when the dispersed phase has an affinity for the dispersion medium, the colloid is termed as lyophilic colloid.
Examples – rubber, starch, protein, etc.
Lyophobic colloids –
It is described as when the dispersed phase has little or no affinity for the dispersion medium, the colloid is termed as lyophobic colloid.
Examples – Solutions of metals like gold and silver, metallic hydroxides sol, etc.
A Lyophobic Colloid contains large molecules which do not properly dissolve in liquids. The term Lyophobic comes from “Lyo” means solvent and “Phobic” means hating. When such colloidal substances dissolve in a liquid, a very weak attraction force forms between the liquid molecules and colloidal particles and the system does not readily become a colloidal solution.
Major proteins present in Milk:
Casein and whey protein are the major proteins among other proteins present in milk. The quantity of Casein is around 80% which is 29.5 g/L of the total protein in bovine milk, whereas whey protein quantity is around 20% which is 6.3 g/L of the milk. The nitrogen is also present in milk, it is distributed among different proteins such as caseins has around 75% nitrogen content, whey proteins has 18% of nitrogen content, and other miscellaneous proteins has around 2% of nitrogen and non-protein nitrogen is 5%.

So the major lyophobic colloid in the milk is Casein and whey protein.

Note:
As lyophobic colloidal particles are not able to mix with a liquid so it is difficult to prepare and various special techniques are used to ensure that the colloidal particles are mixed in the liquid. Generally all lyophobic solutions are less stable because a weak force of attraction exists between the liquid particles and colloidal particles. If a very small quantity of electrolyte is added in such solutions, they become very unstable and form precipitate. The nature of lyophobic colloidal solutions is irreversible.