Free iodine is titrated against standard reducing agent usually with sodium thiosulphate , i.e.
`K_(2)Cr_(2)O_(7) + 6Kl + 7H_(2)SO_(4) to Cr_(2)(SO_(4))_(3) + 4K_(2) SO_(4) + 7H_(2)O+l_(2)`
` 2CuSO_(4) + 4Kl to Cu_(2)l_(2) + 2K_(2)SO_(4) + l_(2)`
` l_(2) + Na_(2)S_(2)O_(3) to 2Nal + Na_(2)S_(4)O_(6)`
In iodometric titration, starch solution is used as an indicator. Starch solution gives blue or violet colour with free iodine .At the end point , blue or violet colour disappears when iodine is completely changed to iodide.
A ` 1.1` g sample of copper ore is dissolved and `Cu^(2+)` (aq). is treated with Kl . `l_(2)` liberated required `12.12" ml of " 0.1 M Na_(2)S_(2)O_(3)` solution for titration . The % of Cu in the ore is

Options

A. `2.5%`
B. `7%`
C. `5.8%`
D. `4.2%`

Answer

B