Recently I was trying to balance a redox chemical equation:
$$\ce{CuSCN + KIO3 + HCl <=> CuSO4 + KCl + HCN + ICl + H2O}$$
The equation is in principle simple to solve; one element ($\ce{I}$) is reduced and two elements ($\ce{Cu}$, $\ce{S}$) are oxidized. The number of exchanged electrons in both cases must be the same. However, my problem is that I don't know how to assign the oxidation number to sulfur in a thiocyanate anion.
Later, I solved the equation using the matrix method and via obtained reaction coefficients ($4$, $7$, $14$, $4$, $7$, $4$, $7$, $5$) and concluded that the oxidation state of sulfur in thiocyanate is zero. This result is very surprising, because the oxidation number zero in heteroatomic molecules is not common.
My questions are:
- How to assign the oxidation number in such cases?
- How is it possible that oxidation number of an atom bound to a more eletropositive atom is zero?
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