Video: Unique reaction of the thiosulfate ion

A unique reaction of the thiosulfate ion is that with cold iron(III) ion. A deep purple complex is formed:

Fe3+(aq) + 2 S2O32-(aq) ® [Fe(S2O3)2]+(aq)

Upon warming, the iron(III) ion is reduced to iron(II) ion.

[Fe(S2O3)2]-(aq) + Fe2+(aq) ® 2 Fe2+(aq) + S4O62-(aq)