Question

Consider the redox reaction below.

Upper M g (s) plus Pper f e superscript 2 plus (a q) right arrow upper M g superscript 2 plus (a q) plus upper F e (s).

Which equation is a half reaction that describes the reduction that is taking place?
Upper F e superscript 2 plus (a q) plus 2 e superscript minus right arrow upper F e (s).
Upper M g (s) right arrow upper M g superscript 2 plus (a q) plus 2 e superscript minus.
Upper Fe superscript 2 plus (a q) right arrow upper F e (s) plus 2 e superscript minus.
Upper M g (s) plus 2 e superscript minus right arrow upper Mg superscript 2 plus (a q).

Answer 1

Reduction is gain of electrons. Fe2+ is reduced to Fe by gaining 2 e−, so the correct half-reaction is:

Fe2+(aq) + 2 e− → Fe(s)

(For completeness, the oxidation half-reaction is Mg(s) → Mg2+(aq) + 2 e−.)