2.48 g of hydrated sodium thiosulphate `(Na_2S_2O_3 .xH_2O)` was dissolved per litre of the solution. 25 mL of this solution required 12.5 mL of M /100 iodine solution . Determine the value of x.

Explanation

The balanced chemical equation is :
`2Na_2S_2O_3+I_2 rarr Na_2S_4O_6+2NaI`
Let the morality of `Na_2S_2O_3.xH_2O` be `M_1`
Applying morality equation
`((M_1V_1)/n_1)_(Na_2S_2O_3)=((M_2V_2)/n_2)_(I_2)`
`(M_1xx25)/2-=1/100xx(12.5)/1`
`M_1=(12.5xx2)/(100xx25)=0.01M`
Molecular wt. of `Na_2S_2O_3.xH_2O`
`=2xx23+2xx32+3xx16+xxx18`
Amount of `Na_2S_2O_3.xH_2O=0.01xx(158+18x)g`
But actural amount = 2.48 g
`:.0.01(158+18x)=2.48`
`(158+18x)=(2.48)/(0.01)=248`
`18x=248-158=90`
`:. x = 90 / 18 =5`.