Iodine titration can be iodemotire or iodimetric depending on using iodine directly or indirectly as an oxidising agent in the redox titration.
a) Iodimetric titration in which a standard iodine solution is used as an oxidant and iodine is directly or indirectly titrated against a reducing agent. For example `2CuSO_(4)+4KIrarrCu_(2)I_(2)+2K_(2)SO_(4)+I_(2)`
b) Iodimetric procedures are used for the determination of strength of reducing agent such as thiosulphates, sulphites, arsenties and stannous chloride etc., by titrating them against standard solution of iodine in a burette.
`2Na_(2)S_(2)O_(3)rarr2NaI+Na_(2)S_(4)O_(6)`
Starch is used as indicator near the end point which form blue colour complex with `I_(3)^(-)`. The blue colour disappeams when there is no more of free `I_(2)`.
When 319.0 gm of `CuSO_(4)` in a solution is related with excess of 0.5 M KI solution, then librated iodine required 200 ml of 1.0 M `Na_(2)S_(2)O_(3)` for complete relation. The percentage purity of `CuSO_(4)` in the sample is

Options

A. `10%`
B. `20%`
C. `5%`
D. None of these

Answer

C

Explanation

Eq. `CuSO_(4)=Eq.S_(2)O_(3)^(-2)`
`(W)/(159.5)=1xx(100)/(1000)xx1impliesW=15.95gm`
`%CuSO_(4)=(15.95)/(319)xx100=5%`