A `2.5g` sample containing `As_(2) O_(5) Na_(2) HAsO_(3)` and inert substance is dissolved in water and the `pH` is adjusted to neutral with excess of `NaHCO_(3)`. The solution is titrated with `0.15M I_(2)` solution, requiring `11.3 mL` to just reach the end point, then the solution is acidified with `HCl, KI` is added and the liberated iodine requires `41.2 mL` fo `0.015M Na_(2)S_(2)O_(3)` under basic conditions where it converts to `SO_(4)^(2-)`. Calculate per cent compositon of mixture.
