h202 as oxidising agent
jonathan wright
agent and a gas was given off. Everyone tells me this is oxygen but I went
and looked in the library to check and now I am baffled.
The H2O2 was used to oxidise Co2+ to Co3+. I think it should go by the
reaction below;
2(Co2+) + H2O2 + 2(H+) -> 2(Co3+) + 2(H2O)
(In fact (NH4)+ was present so;
2(Co2+) + H2O2 + 2(NH4)+ -> 2(Co3+) + 2(H2O) + 2NH3 (gas evolved)
could we have a vote as to whether this makes sense?)
I have found references to H2O2 being used as a reducing agent and here
oxygen is given off, also when H202 decomposes, but not when it oxidises
something.
Could someone mail me a reaction where H2O2 acts as an oxidising agent and
oxygen is evolved. (A reaction that I can find in the library, not one you
just made up)
Many thanks,
Jonathan Wright
Jesus College
Cambridge
(jp...@cam.ac.uk)
Captain Entropy
jp...@hermes.cam.ac.uk (jonathan wright) wrote:
This can't happen. Peroxide is O(-I). For it to function as an oxidizing
agent it must itself be reduced, and reduction can only lead to O(-II), as
in H2O. Formation of O2, which is O(0), can only occur if O(-I) undergoes
oxidation, i.e. functions as a reducing agent. However, H2O2 tends to
decompose in the presence of various catalysts, including transition
metals. Probably what is going on here is that the H2O2 oxidized Co+2 to
Co+3, but the excess H2O2 was decomposed catalytically, forming O2. If
NH3 were formed in aqueous solution, it would most likely dissolve with no
noticeable evolution of gas. With Co+3 present, it should form NH3-Co+3
complexes.
--
.delta. S
John Milligan
: I need some help with a chemistry practical, H2O2 was used as an oxidising
: agent and a gas was given off. Everyone tells me this is oxygen but I went
: and looked in the library to check and now I am baffled.
: The H2O2 was used to oxidise Co2+ to Co3+. I think it should go by the
: reaction below;
: 2(Co2+) + H2O2 + 2(H+) -> 2(Co3+) + 2(H2O)
: (In fact (NH4)+ was present so;
: 2(Co2+) + H2O2 + 2(NH4)+ -> 2(Co3+) + 2(H2O) + 2NH3 (gas evolved)
: could we have a vote as to whether this makes sense?)
: I have found references to H2O2 being used as a reducing agent and here
: oxygen is given off, also when H202 decomposes, but not when it oxidises
: something.
: Could someone mail me a reaction where H2O2 acts as an oxidising agent and
: oxygen is evolved. (A reaction that I can find in the library, not one you
: just made up)
: Many thanks,
: Jonathan Wright
: Jesus College
: Cambridge
: (jp...@cam.ac.uk)
Just look in a general chemistry text (any one should do). The book
should have a list of half reactions for various substances. The half
reaction listed in General Chemistry by Ebbing (Chapter 13, p.546 Table
13.5) for hydrogen peroxide in a basic medium is
H2O2(aq) ----> O2(g) + 2H(+) (aq) + 2 e(-)
This is valid for your reaction since the ammonium ion creates a basic
medium.
John Milligan
Los Angeles Valley College, California State University - Los Angeles
Department of Chemistry
Captain Entropy
wrote:
Yes, but H2O2 is functioning here as a REDUCING agent--excess electrons on
the RHS. H2O2 CANNOT function as an oxidant AND evolve O2 in the same
rxn.
--
.delta. S
John Milligan
> > Just look in a general chemistry text (any one should do). The book
> > should have a list of half reactions for various substances. The half
> > reaction listed in General Chemistry by Ebbing (Chapter 13, p.546 Table
> > 13.5) for hydrogen peroxide in a basic medium is
> >
> > H2O2(aq) ----> O2(g) + 2H(+) (aq) + 2 e(-)
> >
> > This is valid for your reaction since the ammonium ion creates a basic
> > medium.
> >
> > John Milligan
> > Los Angeles Valley College, California State University - Los Angeles
> > Department of Chemistry
>
> Yes, but H2O2 is functioning here as a REDUCING agent--excess electrons on
> the RHS. H2O2 CANNOT function as an oxidant AND evolve O2 in the same
> rxn.
>
> --
>
> .delta. S
>
about this. Mea culpa.
>
>
>
>
>
>
>
>
>
Harald Teicher
: I need some help with a chemistry practical, H2O2 was used as an oxidising
: agent and a gas was given off. Everyone tells me this is oxygen but I went
: and looked in the library to check and now I am baffled.
: The H2O2 was used to oxidise Co2+ to Co3+. I think it should go by the
: reaction below;
: 2(Co2+) + H2O2 + 2(H+) -> 2(Co3+) + 2(H2O)
: (In fact (NH4)+ was present so;
: 2(Co2+) + H2O2 + 2(NH4)+ -> 2(Co3+) + 2(H2O) + 2NH3 (gas evolved)
: could we have a vote as to whether this makes sense?)
: I have found references to H2O2 being used as a reducing agent and here
: oxygen is given off, also when H202 decomposes, but not when it oxidises
: something.
: Could someone mail me a reaction where H2O2 acts as an oxidising agent and
: oxygen is evolved. (A reaction that I can find in the library, not one you
: just made up)
: Many thanks,
: Jonathan Wright
: Jesus College
: Cambridge
: (jp...@cam.ac.uk)
try (in the prescence of catalase): H2O2 -> H20 + 1/2O2
a.k.a. the Mehler Reaction, photosynthetic electron transport
Harry
Gerald L. Hurst
>>
>This is valid for your reaction since the ammonium ion creates a basic
>medium.
Actually, the ammonium ion is slightly acidic, i.e. it wields a proton
rather than accepting one.
Jerry