2
$\begingroup$

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?

Improve this question
$\endgroup$
2
  • 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. $\endgroup$
    – Ivan Neretin
    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. $\endgroup$
    – Jason Patterson
    Sep 3, 2015 at 23:49

2 Answers 2

Reset to default
3
$\begingroup$

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

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

Improve this answer
$\endgroup$
-1
$\begingroup$

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.

Improve this answer
$\endgroup$
2
  • 3
    $\begingroup$ 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. $\endgroup$
    – Ivan Neretin
    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

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.