Write the balanced chemical equations involved in the preparation of `KMnO_4` from pyrolusite ore `(MnO_2)`.
OR
Write the balanced ionic equations showing the oxidising action of acidified dichromate `[Cr_(2) O_(7)^(2-) ]` solution with (i) Iron (II) Ion and (ii) Tin (II) ion.

Explanation

`2MnO_(2) + 4KOH + O_(2) to 2K_(2) MnO_(4) + 2H_(2) O`
`3MnO_(4)^(2-) + 4H^(+) to 2MnO_(4)^(-) + MnO_(2) +2H_(2) O`
OR
(i) `Cr_(2) O_(7)^(2-) + 14H^(+) +6Fe^(2+) to 2Cr^(3+) +6Fe^(3+) + 7H_(2)O`
(ii) `Cr_(2) O_(7)^(2-) +14H^(+) + 3Sn^(2+) to 2Cr^(3+) +7Sn^(4+) +7H_(2) O`