Three different solution of oxidising agents. `K_(2)Cr_(2)O_(7),I_(2), and KMnO_(4)` is titrated separately with `0.19g of K_(2)S_(2)O_(3)`. The molarity of each oxidising agent is 0.1 M and the reaction are:
(i). `Cr_(2)O_(7)^(2-)+S_(2)O_(3)^(2-)toCr^(3+)+SO_(4)^(2-)`
(ii). `I_(2)+S_(2)O_(3)^(2-)toI^(ɵ)+S_(4)O_(6)^(2-)`
(iii). `MnO_(4)^(ɵ)+S_(2)O_(3)^(2-)toMnO_(2)+SO_(4)^(2-)`
(Molecular weight of `K_(2)S_(2)O_(3)=190,K_(2)Cr_(2)O_(7)=294,KMnO_(4)=158, and I_(2)=254 mol^(-1))` Which of the following statements is/are correct?

Options

A. All three oxidants can act as self-indicators
B. Volume of `I_(2)` used is minium
C. Volume of `K_(2)Cr_(2)O_(7)` used is maximum
D. Wt. of `KMnO_(4)` used in the titration is max

Answer

A, B, D

Explanation

All three are self indicators i.e, they do not need any indicator for titration.
`K_(2)S_(2)O_(3) = (0.19)/(190) = 10^(-3)mol` = 1 mmol
(i) mEq of `S_(2)O_(3)^(2-) (n = 8) = ` mEq of
`Cr_(2)O_(7)^(2-) (n = 6), 1 xx 8 = 0.1 xx 6 xx V`
`:. V_(Cr_(2)O_(7)^(2-)) = (80)/(6)mL`
(ii) mEq of `S_(2)O_(3)^(2-) (n = 1)=` mEq of `I_(2) (n = 2)`
`1 xx 1 = 0.1 xx 2 xx V :. V_(I_(2)) = 5 mL`
(iii) mEq of `S_(2)O_(3)^(2-) (n = 8)` = mEq of
`MnO_(4)^(-) (n = 3) , 1xx 8 = 0.1 xx 3 xx V`
`:. V_(MnO_(4)^(-)) = (80)/(3)mL`
Also,
Weight of `K_(2)Cr_(2)O_(7) = 8 xx (294)/(6) xx 10^(-3) = 0.392g`
Weight of `I_(2) = 1 xx (254)/(2) xx 10^(-3) = 0.127g`
Weight of `KMnO_(4) = 8 xx (158)/(3) xx 10^(-3) = 1.264g`