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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: /0 on November 15, 2008, 10:02:51 pm

Title: Identifying a redox
Post by: /0 on November 15, 2008, 10:02:51 pm: Which of the following equations is a redox reaction?

A. $Pb^{2+} (aq)+H_2S(aq) \rightarrow PbS(s)+2H^+(aq)$

B. $I_2(s)+2OH^-(aq) \rightarrow I^-(aq)+OI^-(aq)+H_2O(l)$

C. $SO_2(g)+2H_2O(l) \rightarrow HSO_3^-(aq)+H_3O^+(aq)$

D. $PO_4^{3-}(aq) + H_2O(l) \rightarrow HPO_4^{2-} (aq)+OH^-(aq)$

The answer is B

But I don't understand why?!
Title: Re: Identifying a redox
Post by: Matt The Rat on November 15, 2008, 10:13:09 pm: Change in oxidation numbers. $I_2(s)$ has 0 as an oxidation number then $I^-(aq)$ has -1 as an oxidation number. Just look for a change in oxidation number and you'll find the redox reaction.
Title: Re: Identifying a redox
Post by: /0 on November 15, 2008, 10:18:40 pm: Thanks Matt the Rat,

But in $IO^-$ the $I$ has an oxidation number of +1, so would the $I_2$ be the oxidant or the reductant?
Title: Re: Identifying a redox
Post by: Wizard on November 15, 2008, 10:50:28 pm: As the oxidation number of Iodine has increased to +1 and -1, it acts as both a reductant and an oxidant

I think... :)
Title: Re: Identifying a redox
Post by: nerd on November 15, 2008, 11:53:13 pm: Is that even possible, for a substance to act as an oxidant and reductant at the same time?