All titration which involves the direct titration of Iodine with a reducing agent are grouped under lodimetry. Iodimetry is employed to determine the strength of reducing agent such as sodium thio sulphate I_(2) + 2Na_(2)S_(2)O_(3) rarr 2I^(-)+S_(4)O_(6)^(-) If iodine is liberated as a result of chemical reaction involving oxidation of an idodide ion by a strong oxidizing agent in neutral or acidic medium the liberated iodine is then titrated with reducing agent. This titration is called lodometry. Todometry is used to estimate the strength of oxidizing agent. For example the estimation of Cu^(++)with thiosulphate. Cu^(+ +) +I^(-) Cu_(2)I_(2)+I_(2) , I_(2)+S_(2)O_(3)^(-) rarrS_(4)O_(6)^(-) +I^(-) Starch used as indicator near the end point which form blue colour complex with I_(3)^(-) . The blue colour disappears whenWhen 159.50g of CuSO_4in a solution is reacted with KI, then the liberated iodine required 100 ml 1 M Na_(2)S_(2)O_3for complete reaction, then what is the percentage purity of sample used in making the solution.