If ` 10.0 mL` of hypo solution `(Na_2S_2O_3. 5H_2 )` is decolorized by `15 mL` of `M//40` iodine solution , then the concentration of hypo solution is `"____" g dm^(-3)`.

Explanation

The balanced equation for the redox reaction is `2S_(2)O_(3)^(2-)+I_(2) rarr2 I^(-)+S_(4)O_(6)^(2-)`
From the balanced equation it is evident that 2 moles of `Na_(2)S_(2)O_(3)=1 "mole of" I_(2)` applying molarity equation we have
`(M_(1)V_(1))/(n_(1))(Na_(2)S_(2)O_(3))=(M_(2)V_(2))/(n_(2))(I_(2)) or (M_(1)xx10)/(2)=(15xx1)/(1xx40) or M_(1)=(15xx1xx2)/(10xx40)=3/40`
thus the molarity of hte hypo solution `=3//40` M
Mol mass of `Na_(2)S_(2)O_(3)5 H_(2)O=248 g "mol"^(-1)`
`therefore` Concentration of `Na_(2)S_(2)O_(3)5H_(2)O=(248xx3)/(40)=18.6 dx^(-3)`