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)`.

Options

A. ` 24.6`
B. ` 8.6`
C. ` 18.6`
D. ` 31.6`

Answer

C

Explanation

The balanced equation for the redox reaction is
` 2S_2O_3^(2-) + I_2 rarr 2I^(-) +S_4O_6^(2-)`
Applying molarity equation , we have
` (M_1V_1) /n_1 (Na_2S_2O_3) = (M_2V_2)/n_2 (I_2)`
`(M_1(10 mL))/2 = ((1//40) (15 mL))/1`
or ` M_1 = (1xx 15 xx 2)/(10xx 40) = 3/(40) "mol L"^(-1)`
Strenght of hypo solution ` = ("Molarity" ) xx ("Molar Mass")`
` =(3/(10) "mol L"^(-1)) (248 "gmol"^(-1))`
` =18.6 "g L"^(-1)`
` =18.6 "g dm"^(-3)`.