Alyophobic sol containing gelatin does not coagulate on addition of salt.Why?

Question

Alyophobic sol containing gelatin does not coagulate on addition of salt.Why?

Answer 1

Depends also on the pH of the solution when the salt is added and the iso electric point pH of the gelatine (i.e. the pH at which there is no net charge on the gelatine layer in this case). This is normally pH 9 for porkskin gelatins or pH 5-6 for beef gelatines.

So if your sol pH is just under neutral, use a pigskin geltine to ensure maximum stability and if alkaline, use a beef gelatine. If your "salt" is not sodium chloride, (i.e. calcium chloride or sodum phosphate), the the "salt " will affect the pH and change the stability of the system. Actually, given enough salt in solution, the sol will eventually coagulate anyway.

Answer 2

Gelatin form a thin protective layer around particles of dispersed phase which prevents neutralisation of charge by the ions of salts.Hence, no coagulation occurs.