Thread: HELP!! PLEASE!! hydrogen peroxide in acidic conditions?

please help i am doing an investigation into the rate of decomposition of hydrogen peroxide and as an extention i looked into the rate in acididic and alkaline conditions, thinking that le chatiers principle would make it shift to the right under acidic conditions and thefore the rate of reaction would be faster, however i cannot find anything written supporting my theory, is there any one out there that can help apart from my tutors who r refusing!! thankyou sooo much!!

H2O2 Is Alkeline, is it not ?

Therefore adding an acid would slow down any reaction by reducing its Ph value towards 7.

Hydrogen peroxide is weakly acidic, though I'm not sure what effect this has on the reaction 2H₂O₂ --> 2H₂O + O₂ since acid/base isn't involved in this equilibrium.

I believe hydrogen peroxide is sensitive to alkaline pH but I'm not sure how much, or what the mechanism is... perhaps something like

H₂O₂ + OH^- --> HOO^- + H₂O

HOO^- + OH^- --> H₂O + O₂

I dunno, I have no evidence for that random guess.

Still, I don't think Le Chatelier's principle will explain anything for you because this isn't an equilibrium, it's a spontaneous exothermic decomposition. Le Chatelier's principle tells you about position of equilibrium (ie forward and backward reaction rates are equal) - this is about rate constant for the forward reaction only - there is no equilibrium since one of your products, oxygen, is escaping.

There is a catalyst for decomposition under acidic conditions which is something like KI, for example.

Originally Posted by Matt Lacey

Hydrogen peroxide is weakly acidic

REALLY? I thought H2O2 was a bleaching agent and therefore alkaline ?

it is a bleaching agent, they use it in blonde hair dyes

Being a bleach says nothing about it's acidity just that it is an oxidising or reducing agent.

it's an alkaline, it has a Ph of 11.65

'Nuff Said.

Originally Posted by Nevyn

it's an alkaline, it has a Ph of 11.65

11.65 is the pKa value which is the log of the acid dissociation constant not the pH. As pH is a measure of the dissociation of Hydroxide ions, its value is entierly dependant on the concentration of the solution. If you look at the pH values for hydrogen peroxide at different concs it is indeed weakly acidic as it will readily dissociate to donate H+ ions.

To give a rough idea of Hydrogen Peroxides acidity a 10% solution will have a pH of around 5.5 and a 60% solution of 4.5.

oops, sorry Leo, looks like i made a mistake :?

Peroxide reacts with most acids to form a peracid, your solution will still be acidic

Hello to all! I'm new on this Forum

Originally Posted by xjessiemagoox

please help i am doing an investigation into the rate of decomposition of hydrogen peroxide and as an extention i looked into the rate in acididic and alkaline conditions, thinking that le chatiers principle would make it shift to the right under acidic conditions and thefore the rate of reaction would be faster, however i cannot find anything written supporting my theory, is there any one out there that can help apart from my tutors who r refusing!! thankyou sooo much!!

When you say "rate of decomposition" you mean the speed of the reaction:
H2O2 --> H2O + (1/2)O2
or you mean the reaction's speed with a reducing substance? It's not the same thing.
Furthermore, what you talk about Le Chatelier Principle, refers to the reaction's equilibrium constant, that is, the amount of products relative to the amount of reagents, and not to the reaction's rate.

Originally Posted by leohopkins

H2O2 Is Alkeline, is it not ?

Therefore adding an acid would slow down any reaction by reducing its Ph value towards 7.

H₂O₂ is a weak acid, but it can be basic under very acidic conditions, forming a [H₃O₂]⁺ ion.

Originally Posted by Chemboy

Originally Posted by leohopkins

H2O2 Is Alkeline, is it not ?

Therefore adding an acid would slow down any reaction by reducing its Ph value towards 7.

H₂O₂ is a weak acid, but it can be basic under very acidic conditions, forming a [H₃O₂]⁺ ion.

Yes, H₂O₂ is a bit more acid than H₂O, even if I wouldn't say it's a weak acid: its Ka is 10^-11.65.

It's true that it can be basic under very acidic conditions forming [H₃O₂]⁺. It is more difficult than with water, however,

so H₂O₂ is less basic than water (and so [H₃O₂]⁺ is more acid than H₃O⁺), but I don't know how much.

I would like to know it.