Question

Write a net ionic equation for the following: Acidified solutions of sodium dichromate and copper (I) bromide are mixed?

I know that the `Cr_2O_7^{2-}` will reduce to `Cr^{3+}`, but what isn't immediately obvious to me is why `Cu^+` is oxidized into `Cu^{2+}` how do we know necessarily that the copper oxidizes, and that it specifically oxidizes to copper(II).

There was also another problem where `Fe^{2+}` was oxidized to `Fe^{3+}`. In general, how do we know whether or not the metals oxidize, and what specifically they oxidize to.

Answer 1

Well, usually these redox equations follow standard protocols....

Explanation:

`Fe(II+)` is oxidized to `Fe(III+)`.....`Cu(+I)` is oxidized to `Cu(+II)`...at A level, it is usually made clear as to the individual redox process that occur. At undergraduate level you would have to be mindful of standard redox processes.

Here, we know that red-orange dichromate ion, a potent oxidant, is reduced to green `Cr^(3+)`....(there was an old song about `"the orange and the green"`, it referred to sectarian division in Northern Ireland)...

`Cr_2O_7^(2-) +14H^+ + 6e^(-)rarr 2Cr^(3+) + 7H_2O(l)` `(i)`

`underbrace(Cr(VI+))_"red-orange"rarr`

`underbrace(Cr(III+))_"green"`

And for every reduction there is a corresponding oxidation...

`Cu^+ rarrCu^(2+) + e^(-)` `(ii)`

And so for the final redox process we take... `(i)+6xx(ii)`

`Cr_2O_7^(2-) +14H^+ + 6Cu^(+)rarr 2Cr^(3+) + 6Cu^(2+) +7H_2O(l)`

....the which I think is balanced with respect to mass and charge...