Question

Chemical Principles involved in the preparation of Lyophillic and Lyophobic sol.

Answer 1

Colloidal sols are divided into two categories: 

1. Lyophillic sol- Solvent attracting 

2. Lyophobic sol- Solvent repelling 

• Lyophillic sols are more stable than the lyophobic sols because in lyophillic sols, particles of dispersed phase have an affinity for the particles of dispersion medium. 

• Factors responsible for the stability of sols are: 

1. Charge 

2. Solvation of the colloidal particles by the solvent. 

• Lyophillic sols are stable due to the solvation factor. 

• Lyophobic sols are stable due to the charge on the colloidal particles. Charges can be positive or negative. 

• Examples of lyophillic sols are Egg albumin, starch and gum. 

• Examples of lyophobic sols are freshly prepared ferric hydroxide, aluminium hyroxide and arsenic sulphide. 

• Positively charged sols- hydrated ferric oxide (when FeCl₃ is added to excess of hot water) 

• Negatively charged sol- starch, arsenious sulphide and hydrated ferric oxide (when FeCl₃ is added to NaOH solution). 

• Lyophillic sols are directly formed by mixing and shaking the substance with a suitable liquid.

• Lyophobic sols cannot be prepared by direct mixing and shaking. 

• Some methods for the colloids preparation are

a) Chemical methods 

b) Electrical disintegration 

c) Peptization. 

• Sols are purified by dialysis.