How are the end points of titrations detected in the following reactions ?
a) `MnO_(4)^(-2)` oxidises `Fe^(2+)`
b) `Cr_(2)O_(7)^(2-)` oxidises `Fe^(2+)`
c) `Cu^(+2)` oxidises `I^(-)`

Explanation

a) In the oxidation of `Fe^(2+)` with `MnO_(4)^(-)`, the permanganate it self act as self indicator. `MnO_(4)^(-)` has purple colour. The visible end point in this case is achieved after the last amount reductant `(Fe^(2+))` is oxidised and the first stable tinge of pink colour appears.
b) In the oxidation of `Fe^(2+)` with `Cr_(2)O_(2)^(2-)` an indicator such as diphenyl amine is used. Just after the equivalence point the excess `Cr_(2)O_(2)^(2-)` oxidises the diphenyl amine to intence blue colour by which the end point can be detected.
c) In the oxidation of `I^(-)` with `Cu^(2+)` the iodine formed will give intense blue colour with starch. This colour will be discharged with excess of hypo added after the equivalence point.