Redox Chem Question (1 Viewer)

[Aerlinn]

I have this reaction:
2h202 ---> 2H20(l) + O2(g)

Is h2O2 an oxidant or reductant and why? As far as I can see, I can't tell, 'cause it could be both...

Also have have this:
S2O4(²-) (aq) ---> SO3 (²-) (aq)
[Within the brackets are the charges on the ions, 2-]
It says to balance this half equation, but I end up with the wrong answer. Would somebody be able to help me with this? ie. do the question and tell me what they get?

Help for either of these would be greatly appreciated

 

[xiao1985]

H2O2 (peroxide) is usually a moderate oxidant... a rather nasty chemical as well.

if there should be an oxidant, there need to be a reductant... which means in this case, if there is an oxidant, then H2O2 act both as an oxidant and reductant ...

above is my speculation though... a rather strange question i must say...

as for question 2, it's not possible to balance it without addition of a 3rd substituents... product side will always have S:O ratio being 1:3 whilst reactant being 1:2...

unless you put 0 and 0 infront of both, which is trivial...

 

[Aerlinn]

Ah ok. Hmmm... can a species act as both an oxidant and reductant at the same time? Confuzzled :S
As for the second one, think I figured it out, you add water, and hydrogen ions and balance charges with electrons...

 

[xiao1985]

oo... didn't realise you can/need to put more chemicals in... my bad =p

and i dont' think there is an other way out for the question... oxidation state for oxygen in peroxide is I ... in water is II and in oxygen gas is 0... so go figure... one hydrogen peroxide at as a oxidant and it self reduces... having the oxidation number reduced to 0; vice versa

 

[Aerlinn]

Well, I looked up the answer to that redox equation, and it says it's a strong oxidant. I have no idea why... maybe you can figure it out... 'cause I don't know =S

 

[S1M0]

thank god i don't do chemistry this year.

 

[xiao1985]

uhm... because it self reduces readily? because peroxide is not as stable as water or oxygen? hence react/reduce much much readily?! hence a strong oxidant...

thought that being said, you will meet much more stronger oxidant later on... (iirc, there are peroxide in hair bleachers or something like that)

 

[Aerlinn]

Hm, maybe...

 

[xiao1985]

since peroxide is an oxidant, and itself is very very unstable, it can undergo reduction very readily... ie if it touches anything it reduces, and in process, oxidise the thing it touches... hence it's a powerful oxidant...

 

[Aerlinn]

Ah, ok, so I see you've figured it out

So which equations like these, its a matter of knowing the properties of species. Um, do you know whether all peroxides behave similiarly/ are strong oxidants?

since peroxide is an oxidant...

I thought that oxidants and reductants act as oxidants and reductants as part of a redox reaction... are you saying being an oxidant/reductant can exist in a compound or something as an inherent property? ie. in this case with the peroxide
being the oxidant, and that taking prevalence in the reaction...

 

[xiao1985]

my apologies... oxidants and reductants act as oxidants and reductants as part of THE redox reaction... there are nothing inherent about them... they are all relative...

the only reason i say peroxide is an oxidant is because it's more likely to reduce and hence oxidise others comparing to all other chemicals...

 

[Aerlinn]

I see. that makes sense Maybe it just tends to like to oxidise things. You know they should tell us these exceptions, those equations where using oxidation numbers doesn't tell you much as to whether something is oxidant/reductant. I dont suppose you know any other exceptions worth watching out for?

 

[xiao1985]

in fact, in thise stage, i am surprised they even snuck in this exception.... it seems way overthe top for a hsc oriented material...

 

[Aerlinn]

yea, but then, there IS a lot to chemistry...

 

[xiao1985]

hehe, good to see more real chemistry got taught in high school syllabus...

 

[Aerlinn]

^_^