Question

What would likely occur if `"potassium iodide"` were added to `"ferric nitrate"`?

Answer 1

`Fe(NO_3)_3(aq) + 3KI(aq) rightleftharpoons3K(NO_3)(aq) + FeI_3(aq)`

Explanation:

This is a type of metathesis reaction, i.e. a partner exchange reaction. Neither of the products are particularly insoluble, and they would remain in solution as the aquated ions, i.e. `Fe^(3+)`, `I^(-)` etc.

Additional redox reactions are conceivable, i.e. reduction of ferric to ferrous ion, or oxidation of iodide ion to tri-iodide, i.e. `I_3^-`:

`Fe^(3+) +e^(-) rarr Fe^(2+)` `E^(0)=0.77*V`

`I^(-) rarr 1/2I_2 + e^(-)` `E^(0)=-0.54*V`

`3I^(-) rarr I_3^(-) +2e^(-)` `E^(0)=??*V`

Oxidation of the iodide anion might indeed drive the ferric ion reduction. The `E^0` values show that the reaction is certainly thermodynamically feasible.

In the absence of further information, we invoke the given, so-called `"metathesis or partner-exchange reaction"`, which proceeds WITHOUT redox transfer.