What mass of `Na_(2)S_(2)O_(3).5H_(2)O` is needed to make `500 cm^(3)` of `0.200N` solution for the reaction?
`2S_(2)O_(3)^(2-)+I_(2)rarrS_(4)O_(6)^(2-)+2I^(-)`

Explanation

Meq. of `Na_(2)S_(2)O_(3) = 0.2 xx 500 = 100`
`(because Meq. N = xx V_((i n mL)))`
`therefore` `(w)/(M//1) xx 1000 = 100` , `(because Meq. = (wt)/(E.wt) xx 1000)`
or `(w)/(248) xx 1000 =100`
`("Mol. wt" Na_(2)S_(2)O_(3). 5H_(2)O = 248)`
`w = 24.8 g`