An aqueous solution containing 0.10 g `KIO_(3)` (formula weight`=214.0`) was treated with an excess of KI solution the solution was acidified with HCl. The liberated `I_(2)` consumed 45.0 " mL of " thiosulphate solution to decolourise the blue starch-iodine complex. Calculate the molarity of the sodium thosulphate solution.

Answer

`(0.062 M)`

Explanation

The redox reaction involved are:
`IO_(3)^(-) + 5I^(-) + 6H^(+) rarr 3I_(2)+3H_(2)O`
`I_(2) + 2S_(2)O_(3)^(2-) rarr 2I^(-) + S_(4)O_(6)^(2-)`
millimol of `KiO_(3)` used `= (0.1)/(214) xx 1000 =0.467`
`rArr` millimol of `I_(2)` formed `= 3 xx 0.467 = 1.4`
`rArr` millimol of `Na_(2)S_(2)O_(3)` consumed `= 2xx1.4 = 2.8`
`rArr` millimol of `Na_(2)S_(2)O_(3) = (2.8)/(45) = 0.062 M`