Titrations with Titanium III Salts

Ti + is a fairly strong reducing agent. The tendency of TiO + to form complexes transforms TI + into a strong reductor by displacement of the equilibrium toward the left. Titane HI chloride and sulfate are prone to aerial oxidization. Generally, determinations are back titrations. The titane III salts in excess are titrated with a ferric salt with potassium thiocyanate used as the indicator. 

Chromous ions Cr enter into the half-redox equilibrium 

The standard potential value indicates that chromium II ions are a very strong reducing agent. A Pourbaix diagram shows that they are not stable in water. Protons oxidize them according to the reaction (see Fig. 20.3) 

Likewise, they are oxidized by the air dioxygen. They are one of the most reducing titrants. They are easily prepared by the reduction of chromic ions with zinc. They reduce several inorganic and organic species. 

Ascorbic acid is a rather strong reducing agent = 0.185 V (see iodometry, 

---