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The oxidation states of $sp^2$ and $sp^3$ carbon in ethanoic acid are $-3$ if we do not consider the electronegativity difference of these two carbons due to their different hybridisation but this is not the case with the thiosulphuric acid ($\ce{H2S2O3}$); here the oxidation states of sulphur here are +6 and -2. So why are we considering the electronegativity difference of two $sp^3$ and $sp^2$ sulphurs here?

Thiosulfuric acid ethanol

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    $\begingroup$ Welcome to Chemistry! This seems like a homework question. We ‎have a policy which states that you should show your thoughts and/or efforts into solving the ‎problem. It'll make us certain that we aren't doing your homework for you. Otherwise, this ‎question may get closed. $\endgroup$ – bon Jan 31 '16 at 14:08
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Typically when figuring oxidation state of an atom, electronegativity of different atoms of same element is considered equal. This means that in thiosulphate oxidation state of central sulfur would be somewhere around 4.

However! Let us condider a very tricky case: ozone. Technically it consists of atoms of same element and the oxidation state of oxygen atoms should be zero. But ouch, auch, the central atom bears full positive chanrge in all feasible structures.... So, should ozone, disregarding electron shifts in covalent bonds, have oxidation state of atoms +1 (for central atom) and -1/2 (for two other atoms)? But this doesn't make much sense. This is a place where oxidation state abstraction breaks.

So, there are situations when oxidation state abstraction doesn't make much sence.

Thiosulphate is somewhate similar. The central sulfur behaves very muc like sulfur in sulfate, so by analogy it should be in +6 oxidation state. However, formally it is not the case. Here a clear conflict between formal abstraction and real life occurs, so people cope with it variously. One possibility is to arbitrarily say that the central sulfur of thiosulfate is in +6 oxidation state (and it makes sence). Another is to go formally (and it also makes sense). I saw both options in the wild.

TL;DR : formally the central sulfur in thiosulphate is +4; but people sometemes disregard it as the ion is very similar to sulphate with central sulfphur atom being +6.

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  • $\begingroup$ by your explanation it seems that it is some kind of trend that had been set earlier and is followed widely irrespective of definition of oxidation state in some cases like thiosulphuric acid and ethanoic acid ? am i correct ??chemistry.stackexchange.com/users/485/permeakra $\endgroup$ – Kumar Gaurav Feb 11 '16 at 6:58
  • $\begingroup$ @KumarGaurav It's not so much widespread, but it happens. For example, PH3, AsH3 and SbH3 are typically considered as 'reduced' -3 compounds, despite that hydrogen have electronegativity slightly above that of the elements in question. $\endgroup$ – permeakra Feb 11 '16 at 7:33
  • $\begingroup$ @KumarGaurav ethanoic acid is not the case, though. It is typically considered to have -3 and +3 carbons. $\endgroup$ – permeakra Feb 11 '16 at 7:36
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An sp2 carbon is more electronegative than an sp3 carbon but we generally don't consider the electronegative difference of the carbons while calculating the oxidation state.

Carbon is more electronegative than hydrogen hence the sp3 carbon will take the electrons from the hydrogen.

Oxidation state of sp3 carbon = $3(-1)= -3$

The sp2 carbon has a double bonded oxygen which is more electronegative than the carbon hence the carbon atom will lose 2 electrons to the oxygen. The oxygen of the OH group will also steal an electron from carbon hence giving a total of +3 oxidation state to the carbon.

Oxidation state of sp2 carbon = $2(+1) + 1(+1) = 3$

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  • $\begingroup$ exactly , just opposite in the of H2S2O3 (thiosulphuric acid) ,we consider the electronegativity difference of these two sp3 and sp2 sulphur ; why this kind of irregularities is practised in carbon? $\endgroup$ – Kumar Gaurav Feb 1 '16 at 4:06
  • $\begingroup$ why we don,t consider the electronegativity difference of carbons here (being sp2 and sp3 hybridised ) $\endgroup$ – Kumar Gaurav Feb 1 '16 at 8:58

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