Page 100 - Analytical Chemistry I E-book

Titration of Halogen Acid Salts of Bases

• Example: Ephedrine HCl.
• In general, the chloride ions are very weakly basic so that they cannot

react with perchloric acid.
• HCl salts of bases can be titrated using 0.1 M perchloric acid in glacial

acetic acid medium after the addition of mercuric acetate. Hg(Ac)2
replaces the Cl– ions by an equivalent quantity of acetate ion, which is
a stronger base.

Hg(CH3COO)2 + 2Cl– ⎯→ HgCl2 + 2CH3COO–
Mercuric chloride
(unionized salt)

• The CH3COO– formed is titrated with HClO4 titrant using crystal violet
indicator.
CH3COO– + HClO4 ⎯→ CH3COOH + ClO4–