Question:how does pH affect decomposion of H2O2?

[QqMichelle]

I really need help on this lab. it's a gr.12 chemistry lab, i chose the topic of how does the pH affect the rate of catalytic decomposition of H2O2, i'm using KI as the catalyst, and adding HCl or NaOH to change the pH. all we have to do is just the planning part, i need help on explaining why and how the pH of the mixture affect the rate of decomposition of H2O2.

i know in order to speed up a reaction, you either have to have more collision of the particles to occur, or to have higher energy so that more of the particles would have sufficient energy for the collision to be successful. so how does the change in pH contribute to either of these? or there's other reason?

can someone please help me???

please!~ i have to get this done by sunday...2 days away~~T^T

[thedarkshade]

Here is a link to Wiki.

 

As it says that it decomposes spontaneously in water and oxygen gas, then probably the best pH value is neutral (just guessing)!

[QqMichelle]

but would it affect the rate of reaction? being neutral prob would make the decomposition spontanous, but it prob doesn't necessarily speed up the reaction. does it?

[thedarkshade]

pH does affect the speed of the reaction. Here's a short quote from newton website:

Chemical reactions however do not happen at the same speed. Other

factors such as temperature, pH, etc. can have a tremendous affect

on reaction speed. For instance, the reduction of Cr+6 to Cr+3 can

take hours at pH 8, if the pH is <2, the reaction occurs in seconds.

[QqMichelle]

how does pH affect the rate of reaction though? especially in the case of decomposing H2O2?

[thedarkshade]

I don't know the answer really, but someone here could help you figure that out. I never was the chemkid!

[QqMichelle]

thanx anyway!~^^

it's a hypothesis,so i guess i'll just try to make something up~~

would it be when the bonds break into 2 H+ and 2 O-, if there's HO-, it only needs to form 1 H-O bond to produce a H2O, and 1 O=O bond to produce O2, but when there's H+, it needs to form 2 H-O bond and 1 O=O bond to produce H2O and O2. so HO- ions favor the reaction,thus high pH increases the rate of reaction.?

does it sound reasonable?

[Darkblade48]

Hydrogen peroxide often has an acid stabilizer included when it is sold over the counter, i.e. in pharmacies.

 

I have seen the mechanism in an introductory organic chemistry textbook (McMurry), but it's 4:10 am local time, and I don't want to be bothered looking for the mechanism (of both acid and base catalyzed decomposition) at this time....

[thedarkshade]

thanx anyway!~^^

it's a hypothesis,so i guess i'll just try to make something up~~

would it be when the bonds break into 2 H+ and 2 O-, if there's HO-, it only needs to form 1 H-O bond to produce a H2O, and 1 O=O bond to produce O2, but when there's H+, it needs to form 2 H-O bond and 1 O=O bond to produce H2O and O2. so HO- ions favor the reaction,thus high pH increases the rate of reaction.?

does it sound reasonable?

AFAIK the [ce]H2O -> H^+ + OH^-[/ce] dissociation is only theoretical. IIRC the real dissociation is [ce]2H2O -> H3O^+ + OH^-[/ce]