In hydroponics, Hydrogen Peroxide is used to sanitise nutrient solution from pathogens. Allegedly it does not take sides, oxidising aerobic as well as anaerobic, including damaging the roots, so I was told. I believe this argument, since O as a free radical is highly reactive. I would appreciate your input on this. However, this isn't the main question.

The main question is that manufactures also claim that it will provide DO, dissolved oxygen, to the solution. I find this hard to believe. Reason being, DO refers to dissolved $\ce{O2}$ (Dioxide) not Monoxide. When $\ce{H2O2}$ breaks down it breaks down to $\ce{H2O + O}$ (free radical), right?

Can you please put some clarity into this?

  • 4
    $\begingroup$ Whenever the free radicals have nothing to react with, they (being highly reactive) quickly recombine with each other to produce $\mathrm O_2$. So both claims are true. And by "quickly", I mean really quickly. $\endgroup$ Sep 3, 2015 at 23:38
  • $\begingroup$ Also, it is extremely likely that your nutrient solution contains metal ions that will readily act as catalysts to decompose the peroxide you put in the solution. Even a small quantity of iron ions will do the job, for instance. It's likely that by the time you use the solution, the peroxide has already largely decomposed. $\endgroup$ Sep 3, 2015 at 23:49

2 Answers 2


$\ce{H2O2}$ -> $\ce{H2O +1/2O2}$

This might make it easier to understand.

$\ce{H2O2}$ will homolytically cleave for form two $\ce{.OH}$ radicals. Radicals are very reactive and will start a chain reaction, but ultimately you will end up with water and oxygen products from $\ce{H2O2}$.

(Why does it form two hydroxy radicals? because the O-O single bond is weak and unstable - see MO theory)

How do we know this? Look at a bottle of $\ce{H2O2}$ that has been left out of the fridge for too long. There will be a slight pressure build up of $\ce{O2}$ gas and the % concentration $\ce{H2O2}$ will be down due to formation of $\ce{H2O}$and loss of $\ce{H2O2}$.

For sake of completion, You can alternatively balance the equation thus: $\ce{2H2O2 -> 2H2O + O2}$


Hydrogen peroxide is unstable under standard conditions and breaks down into $\ce{H2O + O2}$. Although you are not left with a free radical, diatomic oxygen is still an extremely powerful oxidizing agent, which is the same reason rust forms on metals. So even though it is not a free radical, it still has the ability to oxidize your organic compounds.

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    $\begingroup$ If it would be that simple, hydrogen peroxide would have no advantage over $\mathrm O_2$, which we already have in the air; then why would anyone use peroxide at all? Also, $\mathrm O_2$ is a radical, though that is hardly relevant for the present discussion. $\endgroup$ Sep 4, 2015 at 0:05
  • $\begingroup$ But where did you find the O2? I see 2 atoms Hydrogen and 2 atoms of Oxygen. In your example there would need to be 3 atoms of Oxygen. Do you understand my confusion? Thanks $\endgroup$
    – Daithí
    Sep 7, 2015 at 11:36

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