Question

In the extraction of zinc from zinc blende:

(i) Give an equation to show how zinc oxide is converted to zinc.
(ii) How is impure zinc finally electro-refined? 

Answer 1

(i) \[\ce{\underset{\text{Zinc oxide}}{ZnO} +  \underset{\text{Coke}}{C}->[heated]Zn  + CO↑ }\]

(ii)  Electro-refining of zinc: The electrolyte used: ZnSO₄ solution containing little H₂SO₄.
Anode: Block of impure zinc.
Cathode: Thin sheet of pure zinc.
On passing current zinc is obtained at the cathode.

Anode reaction:  \[\ce{\underset{\text{Impure}}{Zn} -2e^- -> Zn_{(aq)}^{2+}}\]

 Cathode reaction: \[\ce{Zn^{2+}_{(aq)} + 2e^-->\underset{\text{Pure metal}}{Zn}}\]