can be established. It is evident, from the value of the constant, that the chief tendency of the reversible reaction will be toward the reduction of the ferric ions and the liberation of iodine, which is in accord with experience (exp., p. [251]).
It is interesting to note, again, that the reduction of the ferric salt depends on the reduction of the ferric-ion: the ferric-ion may be suppressed, with the aid of potassium fluoride (see p. [255]), and the addition of potassium iodide to a mixture of ferric chloride and potassium fluoride leads to the formation of traces, only, of free iodine (exp.).
Action of Chlorides on Ferric Salts.
For the reaction of chloride-ion on ferric-ion we would have, as in the case of the action of iodide-ion, 2 Fe3+ + 2 Cl− ⇄ 2 Fe2+ + Cl2 and
[Fe3+]2 × [Cl−]2 / ([Fe2+]2 × [Cl2]) = Keq.
For this equilibrium constant we have the relation, as determined above (p. [274]),
| Keq = | KCl−, Chlorine | = | 2E60 | = 2E26. |
| (KFerro, Ferri)2 | (1017)2 |
It is evident, from the value of the equilibrium constant, that the action of chloride-ion on ferric-ion must result quantitatively so differently from the action of the analogous iodide-ion (p. [275]), that the net qualitative results are entirely dissimilar. Whereas in the case of the iodide, liberation of iodine and reduction of the ferric-ion are bound to be the chief and obvious actions, in the case of the chloride-ion, on the other hand, the equilibrium constant demands that there should be no appreciable reduction of the ferric-ion or liberation of chlorine—which is in accordance with our experience (exp., p. [256]).