Does it count as an autoredox reaction if two different elements from the same polyatomic ion or molecule change their oxidation numbers? For example, for a reaction like this:

$$\ce{2KNO3(s) -> 2KNO2(s) + O2(g)}$$

Here, the nitrogen and oxygen in the nitrate ion undergo oxidation and reduction to from nitrite and diatomic oxygen, respectively. Does this count as a redox reaction since the same polyatomic ion undergoes both?

In my text book, it says that when an element in a molecule or polyatomic ion undergoes reduction or oxidation, we refer to the entire molecule or ion as being reduced or oxidized. I don’t know what effect this has on this reaction though.

  • $\begingroup$ Yes, this is a particular type of redox reactions known as disproportionation reactions. $\endgroup$ – ralk912 Mar 25 '18 at 6:55
  • $\begingroup$ Hi dahen! Please use mathjax to format questions and answers! Thanks. $\endgroup$ – MollyCooL Mar 25 '18 at 7:27
  • $\begingroup$ @MollyCooL sorry about that, I'm on phone right now so it was kind of inconvenient to do it $\endgroup$ – Dahen Mar 25 '18 at 7:42

Any reaction in which one atom/ion loses some electrons and any other atom/ion gains those electrons is a redox reaction.

In your particular example, the oxygen atom is losing its electrons and the nitrogen atoms are gaining those electrons. So, it is definitely a redox reaction.

The reaction in which atoms from the same species are oxidised and reduced are called disproportionation reaction. So, the same reaction is also a disproportionation reaction.

Look at these examples too, disproportionation reaction

In both of these examples, the same molecule/ion/atom undergoes an oxidation as well as a reduction, so these are also disproportionation reaction.

Note that every disproportionation reaction is a redox reaction.

  • 1
    $\begingroup$ You should cite figures that you didn't personally make. $\endgroup$ – ralk912 Mar 25 '18 at 7:29

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