10 mL of a potassium dichromate solution liberates iodine from potassium iodide solution. When the iodine was titrated with hypo solution `(N//20)`, the titre value was 15 mL. Find the concentration of dichromate solution in g per litre.

Explanation

The reaction involved may be given as :
`Cr_(2)O_(7)^(2-)+6I^(-)+14H^(+) to 2Cr^(3+)+3I_(2)+7H_(2)O`
`3[I_(2)+2Na_(2)S_(2)O_(3)]to 3[2NaI+Na_(2)S_(3)O_(6)]`
1 mole `K_(2)Cr_(2)O_(7)-=6 " moles of" Na_(2)S_(2)O_(3)`
No. of moles of hypo `=("Mass")/(" M. w. " (158))=(ExxNxxV)/(1000xx158)`
`=7.5xx10^(-4)` mole
No. of moles of `K_(2)Cr_(2)O_(7)=(1)/(6)`[No. of moles of `Na_(2)S_(2)O_(3)]`
Mass of `K_(2)Cr_(2)O_(7)` in 10 mL solution `=1.25xx10^(-4)xx294`
=0.03675 g
Weight of `K_(2)Cr_(2)O_(7)` in 10 mL solution `=3.675 g//L`