Thiosulphate

Dear students, 
Today i am taking up  inorganic chemistry, here i would like to discuss about Thiosulphate. The thiosulphate ion has structure similar  to sulphate ion and may be considered to be derived from sulphate by replacement of an oxygen atom by a sulphur atom. 

Exercise : Sulphur disappears when boiled with an aqueous solution of sodium sulphite.

Thiosulphuric acid spontaneously decompose to sulphurdioxide and sulphur but its salts called thiosulphate are stable.This reaction is used to distinguish between thiosulphate and sulphite because sulphite does not give free sulphur .
Thiosulphates are readily obtained by boiling solutions of sulphite with sulphur.The alkali(sodium) thiosulphate are manufactured for various uses: 

• In photography, thiosulphate are used to dissolve unreacted AgBr from emulsions.

• Sodium thiosulphate solution are used for iodine titration in volumetric analysis (Iodometry and iodimetry)because iodine very rapidly oxidize thiosulphate ions to tetrathionate ion.

• Sodium thiosulphate is colourless crystalline and efflorescent substance.Extremely soluble in water and has a tendency to form super saturated solution.

• It is useful reducing agent due to presenc e of excess of sulphur.It is used in bleaching industry to remove excess chlorine in bleached material.

Question 1:When a few drops of Ferric chloride solution is added to thiosulphate solution a violet colour is obtained which disappears quickly.Explain it.
Question 2:Give me the complexes formed when thiosulphate react with silver bromide(Board Exam)