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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Moss on October 23, 2009, 10:51:47 PM

Title: redox
Post by: Moss on October 23, 2009, 10:51:47 PM

hey
is this oxidation or reduction?

Cr2O72- -> Cr3+
Cr=+6 O=-14 Cr=+3
oxidation number for Cr decreases, so reduction?
H2S -> S
H2S=0,  S=-2
is this reduction? since the oxidation number goes down?


help, thanks

Title: Re: redox
Post by: BetaAmyloid on October 23, 2009, 11:10:12 PM

Remember this, "OIL RIG - Oxidation Involves Losing, Reduction Involves Gaining."

In both of these equations, the product loses in its oxidation state.

So, OIL RIG, Oxidation involves losing.

They are both oxidation - you just had it backwards for the oxidation states.

Hope this helps,
The Cancer Curer

Title: Re: redox
Post by: Moss on October 23, 2009, 11:34:24 PM

the question im trying to do is
balance the fllowing useing the half equation method
Cr2O72- + H2S-> Cr3+ + S

firs step im trying to do is determining whcih one is undergoin reduction and oxidation

can both the half equation be undergoing oxidation?

Title: Re: redox
Post by: BetaAmyloid on October 23, 2009, 11:43:30 PM

Well, I was judging the answer based upon your oxidation numbers - but I believe your oxidation numbers are incorrect. I'm pretty definite that one has to oxidize and one has to reduce, therefore I would conclude that your oxidation numbers are wrong.

Try looking up your oxidation numbers again maybe?

Sorry!
The Cancer Curer

Title: Re: redox
Post by: UG on October 23, 2009, 11:55:42 PM

Quote from: Moss on October 23, 2009, 10:51:47 PM

H2S -> S
H2S=0,  S=-2
is this reduction? since the oxidation number goes down?

No, the first one is reduction, this is oxidation. Your oxidation numbers are wrong, S in H₂S is not 0, it can't be. The oxidation number of any atom(s) which exists as an element is 0.

Title: Re: redox
Post by: Borek on October 24, 2009, 05:30:47 AM

Quote from: The Cancer Curer on October 23, 2009, 11:10:12 PM

They are both oxidation - you just had it backwards for the oxidation states.

Please stop spreading nonsense. You are not helping.