Are all hydrolysis reactions always non redox reactions? For example:

$$\ce{N2O3 + 2H2O -> 2HNO2}$$

The main reason I say that this statement is correct is because oxygen and hydrogen generally show oxidation states of −2 and +1 respectively when bonded to other atoms.

This means that any change in oxidation state needs to take place between the nitrogen atoms involved in the molecular structure and this is very rarely seen.

Hence most (if not all) hydrolysis reactions are non-redox in nature. Is there a mistake in my understanding?

  • 2
    $\begingroup$ Well, that would depend on what's you'll call hydrolysis - I wouldn't call reactions of oxides with water like that. $\endgroup$
    – Mithoron
    May 26, 2021 at 16:17
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    $\begingroup$ Hydration is sure different then hydrolysis, like, an opposite. $\endgroup$
    – Mithoron
    May 26, 2021 at 16:47
  • $\begingroup$ Exception: Hydrolysis of phosphorus pentachloride $\endgroup$ May 27, 2021 at 3:49

2 Answers 2


Hydrolysis refers to any compound reacting with water, including cases where the water acts as an oxidizing or reducing agent. Magnesium silicide, for instance, reduces water leaving both hydrogen and oxygen from the water in negative oxidation states:

$$\ce{Mg2\overset{-4}{Si} + 4\overset{+1}{H}_2O -> 2Mg(OH)2 + \overset{+4}{Si}\overset{-1}{H}_4}$$

  • $\begingroup$ Thanks @andselisk, although I still prefer Roman numerals for oxidation states in formulas to avoid confusion with ion charges. Or is that not convention? $\endgroup$ May 26, 2021 at 15:28
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    $\begingroup$ ONs are Roman when used in nomenclature, otherwise it's recommended to use Arabic numbers in order to avoid confusion with valency, iodine and vanadium symbols. Also, fractional ONs are quite common: how do you type in these with Roman numerals? You cannot confuse charge number with ON because ONs are placed above the element symbol and have preceding sign. Charges are placed in the upper right corner and are followed by the sign. For the IUPAC reference, see, for example, doi.org/10.1515/pac-2015-1204. $\endgroup$
    – andselisk
    May 26, 2021 at 15:38
  • $\begingroup$ @andselisk Apologies for bothering you. Are you certain about your claim here? I ask for three reasons. 1) In the link (or PDF) you provide, the terms "arabic", "above" give 0 hits. In the PDF itself, "roman" gives 1 result: "Similarly, OS as a nomenclature symbol is in roman numerals." But it does not say anything about writing OS in other situations. 2) In the IUPAC Green Book (p 50, 52), OS is explicitly written with Roman numerals in the upper right corner. 3) In IUPAC Red Book, recommendations for formulae (e.g., p 65–66), it is also put the upper right; also says to avoid fractional OS. $\endgroup$ Jun 1, 2021 at 16:07
  • $\begingroup$ @andselisk References as pictures: see here. $\endgroup$ Jun 1, 2021 at 16:25

No. One counter example for the proposed statement would be the case of hydrolysis of dinitrogen tetroxide: $$\ce{N2O4 + H2O -> HNO2 + HNO3}$$ Here, the nitrogen goes from a $+4$ state to a $+3$ and $+5$ in nitrous acid and nitric acid, respectively.

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    $\begingroup$ Sucks to be whoever downvoted this. $\endgroup$ May 26, 2021 at 23:21

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