Iron(III) and iodide reaction

A redox reaction readily takes place in this case. The presence of iron(II) is confirmed by the formation of a Prussian blue precipitate with potassium hexacyanoferrate(III). The production of iodine was evident from the colour change which occurred in this reaction, but is also confirmed by the blue-black colouration which formed on addition of starch solution. The reaction is:

2Fe³⁺(aq) + 2I^-(aq) ⇒ 2Fe²⁺(aq) + I₂(aq)

The reactants were both checked for iron(II) and iodine, and the tests proved negative. This shows that the iodine and iron(II) ions must have been produced when the reactants were mixed and the reaction took place.

Our prediction that this reaction is feasible has been shown to be correct. The positive E_cell value shows that there should be more products than reactants in the reaction mixture at equilibrium.