Question

When the redox equation `Cr^(3+)(aq) + 3Mn(s) -> Mn^(2+)(aq) + Cr(s)` is completely balanced, what will the coefficient of `Cr^(3+)(aq)` be?

Answer 1

`2...........`

Explanation:

Manganese is oxidized:

`stackrel0Mn(s)rarrMn^(2+) + 2e^(-)` `(i)`

Chromium is reduced:

`Cr^(3+) + 3e^(-)rarrstackrel0Cr(s)` `(ii)`

And so we take `3xx(i) + 2xx(ii)` to eliminate the electrons:

`3stackrel0Mn(s)+2Cr^(3+) rarr3Mn^(2+) + 2stackrel(0)Cr`

Charge is balanced, and mass is balanced, and so this is a reasonable representation of reality. Whether the reaction actually works, I don't know, and cannot be bothered to look up redox tables.