Define the following terms with an example in each:

(a) Lyophobic colloids

(b) Homogeneous catalysis

(c) O/W emulsion

OR

Write three differences between Physisorption and Chemisorption.

(a) Lyophobic colloids are those which when mixed with dispersion medium do not form colloids and can be prepared by chemical methods. These are liquid hating substances like metals and their sulphides.

These are easily coagulated on adding small amount of electrolyte or by heating and hence they are unstable.

These are also called irreversible sols because once precipitated they do not give back colloidal solution by simple addition of dispersion medium unlike lyophilic colloids.

(b) Homogeneous catalysis is the one where the reactant and catalyst are in same phase and the process is called homogenous catalysis.

(c) In O/W emulsion, water is the dispersion medium and oil is the dispersed phase. They are unstable and separate in two layers and for their stabilization an emulsifying agent is usually added.

e.g. milk, vanishing cream, etc and the emulsifying agent for O/W emulsions are gum, proteins, etc.

OR