A solution of `0.2 g` of a compound containing `Cu^(2+)` and `C_(2)O_(4)^(2-)` ions on titration with `0.02M KMnO_(4)` in presence of `H_(2)SO_(4)` consumes `22.6mL` oxidant. The resulting solution is neutralized by `Na_(2)CO_(3)`, acidified with dilute `CH_(3)COOH` and titrated with excess of `KI`. The liberated `I_(2)` required `11.3 mL "of" 0.05M Na_(2)S_(2)O_(3)` for complete reduction. Find out mole ratio of `Cu^(2+)` and `C_(2)O_(4)^(2+)` in compound.

Explanation

Let `a` mole of `Cu^(2+)` and `b` mole of `C_(2)O_(4)^(2-)` be present in solution.
Case I. The solution is oxidized by `KMnO_(4)` which reacts with only `C_(2)O_(4)^(2-)`.
`5e+Mn^(7+)rarrMn^(2+)`
`C_(2)^(3+)rarr2C^(4+)+2e`
`therefore "Meq.of"C_(2)O_(4)^(2-)="Meq.of" KMnO_(4)`
`therefore bxx2xx1000=0.02xx5xx22.6`
`therefore b=1.13xx10^(-3)`....(1)
Case II. After oxidation of `C_(2)O_(4)^(2-)`, the resulting solution is neutralized by `Na_(2)CO_(3)`, acidified with dilute `CH_(3)COOH` and then treated with excess of `KI`. The liberated `I_(2)` required `Na_(2)S_(2)O_(3)` for its neutralization, i.e.,
`Cu^(2+)overset(KI)rarrI_(2)overset(Na_(2)S_(2)O_(3))rarrNa_(2)S_(4)O_(6)+I^(1-)`
`therefore` Meq.of `Cu^(2+)="Meq.of"I_(2)` liberated
`="Meq.of" Na_(2)S_(2)O_(3)` used
`{:( :. "Meq if " Cu^(2+)="Meq. of"),(Na_(2)S_(2)O_(3) "used"),(axx1xx1000=1.13xx0.05xx1),( :. a=5.65xx10^(-4)),( :. "Molar ratio of"),((Cu^(2+))/(C_(2)O_(4)^(2-))=a/b=(5.56xx10^(-4))/(1.13xx10^(-3))),(=1/2):}:|{:("Redox changes are: "),(2Cu^(2+)+2etoCu_(2)^(1+)),(2I^(-)toI_(2)+2e),(and 2e+I_(2)to2I^(1-)),(2S_(2)^(2+)toS_(4)^((5//4)+)+2e):}`