Describe the oxidising action of potassium dichromate and write the ionic equations for its.
With (i) iodide (ii) iron (II) solution (iii) `H_(2)S` and (iv) Sn(II)

Explanation

Potassium dichromate is a strong oxidising agent. In acidic solution, its oxidising action may be represented as :
`Cr_(2)O_(7)^(2-)+14H^(+)+6e^(-)rarr2Cr^(3+)+7H_(2)O(E^(@)=1.33V)`
Ionic equations :
i) Reaction of `K_(2)Cr_(2)O_(7)` with I
`Cr_(2)O_(7)^(2-)+14H^(+)+6I^(-) rarr 2Cr^(3+)+3I_(2)+7H_(2)O`
ii) Reaction of `K_(2)Cr_(2)O_(7)" with "Fe^(2+)` (aq)
`Cr_(2)O_(7)^(2-)+14H^(+)+6Fe^(2+)rarr 2Cr^(3+)+6Fe^(3+)+7H_(2)O`
iii) Reaction of `K_(2)Cr_(2)O_(7)` with `H_(2)S`
`Cr_(2)O_(7)^(2-)+8H^(+)+3H_(2)S rarr 2Cr^(+3)+3S+7H_(2)O`