Question

A certain electrochemical cell has for its cell reaction: Zn + HgO rightarrow ZnO + Hg Which is the half-reaction occurring at the anode? a) HgO + 2e^- rightarrow Hg + O_2- b) Zn^2+ + 2e^- rightarrow Zn c) Zn rightarrow Zn^2+ + 2e^- d) ZnO + 2e^- rightarrow Zn

Answer 1

Oxidation occurs at anode:

Oxidation numbers :-

On the left hand : Zn = 0; Hg⁺²O^2- $\Rightarrow$ Hg= +2; O = -2

On the right hand side : Zn⁺²O^2- $\Rightarrow$ Zn= +2, O= -2 ; Hg= 0{in elemental form, oxidation number is zero}

Oxidation is the process of gaining electrons, so it is clear that Zn gains two electrons and Hg loses 2 electrons:

    So, the half reaction, occuring at anode is Zn $\rightarrow$ Zn⁺² + 2e-

And reduction occurs with Hg. In options b and d, Zn is getting reduced. So option c is the answer