Judgment basis: Redox reaction always generates weak reductant and weak oxidant under the action of strong oxidant and strong reductant (the ratio of oxidant on the left and right sides of the reaction, the ratio of reductant on both sides). This is the principle that the reaction must follow spontaneously. Accordingly, there are:

From the reaction of 27 questions, we know that the reduction order is-> S2; Fe2+ ion

Basis: the above inference

According to the reaction order of 28 questions (ferrous oxide first, then SCN), the reduction order is Fe2+>SCN-

Basis: The stronger reducing agent Fe2+ is oxidized first, and the weaker or stronger reducing agent SCN- will be oxidized after it is finished (there is no quantitative discussion here: so generally speaking, ferrous oxide is finished. In fact, strictly speaking, when ferrous oxide is reduced to a very low concentration and the potential of the ferroelectric pair is equal to the potential of N2/SCN para-position, the two reactions begin to proceed at the same time.

General conclusion: the order of reducing force is S2- > Fe2+>SCN-

Finally, I would like to remind you that hydrogen peroxide should not be added to the acidic solution containing SCN-, otherwise, the gas HCN with bitter almond flavor will escape from HSCN→HCN, and you will lie down and see God forever.

Not everyone who does the problem knows that the experiment is safe. It is really misleading! There are hints in the experimental teaching materials of analytical chemistry. In addition, in the important inorganic chemical reaction, there is a reaction!