Iodine titrations: Compounds containing iodine are widely used in titrations, commonly known as iodine titration. It is of two kinds: (i) lodometric titrations (ii) lodimetric titrations. (i) lodometric titrations : It is nothing but an indirect method of estimating the iodine. In this type of titration, an oxidising agent is made to react with excess of KI, in acidic medium or, basic medium in which I_2oxidises into L. Now the liberated I_2can be titrated with Na_(2)S_(2)O_3 .solution. KI overset("Oxidising Agent")rarrI_(2)overset(Na_(2).S_(2)O_(3)//H^(+))rarrI^(-)+Na_(2)S_(4)O_6Although solid I_2is black and insoluble in water, but it converts into soluble I_3ions underset("Black")(I_2(s))+IhArrunderset("Dark brown")(I_3^(-))Starch is used as indicator near the end point or equivalence point. Even small amount of I_2molecules, gives blue colour with starch. The completion of the reaction can be detected when blue colour disappears at the and point. In iodimetric titration, the strength of reducing agent is determined by reacting it with I_2When 214 g of KIO_3reacts with excess of KI in presence of H^(+)then it produces I_2Now I_2is completely reacted with 1 MNa_(2)S_(2)O_3solution in basic medium, where it converts into SO_4^(-2)ions. Then what volume of Na_(2)S_(2)O_3is needed to react the end point of the reaction?