Page 137 - Pharmaceutical_Analytical_Chemistry_1_Theoretical_Notes_Level_1

Mansoura National University
Pharm D-Clinical Pharmacy Program Level 1 Pharm. Anal. Chem. 1 (PC 101)

Conditions that govern the choice of a suitable adsorption indicator:

1. The indicator ion must be of opposite charge to the ion of the precipitating agent.

2. The indicator ion should not be adsorbed before the particular compound has been

completely precipitated, but it should be strongly adsorbed immediately at the

equivalence point.

Note:

- - - -
Eosin is used for the determination of Br , I and SCN and not used for Cl

.......... Why?

-
➢ Because eosin anion is strongly adsorbed by AgCl ppt than Cl and so it will

-
replace some Cl in the primary adsorbed layer giving too soon end point before the

equivalence point.

- -
➢ But in case of Br and I , they are more strongly adsorbed than eosin anion and are

not replaced by eosin.

pH of the medium

132