WAEC Chemistry 2018 Paper

Concept:Oxidation state is the charge an atom appears to have when electrons are counted by electronegativity rules.Explanation:The given reaction is:$$2\mathrm{FeCl}_3 + \mathrm{H_2S} \rightarrow 2\mathrm{FeCl}_2 + 2\mathrm{HCl} + \mathrm{S}$$Chlorine always has an oxidation state of $-1$ in these compounds.In $\mathrm{FeCl}_3$, let the oxidation state of iron be $x$.Then, $x + 3(-1) = 0$, so $x = +3$.In $\mathrm{FeCl}_2$, let the oxidation state of iron be $y$.Then, $y + 2(-1) = 0$, so $y = +2$.Therefore, iron changes from $+3$ to $+2$.This is a reduction because the oxidation state decreases.Answer:The change in the oxidation state of iron is from $+3$ to $+2$.Correct option: C. $+3$ to $+2$.