Zinc and its Compounds
Ores : Zincite (red zinc ore) ZnO, Franklinite (ZnOFe2O3), Zinc blende (ZnS), Calamine Zinc spar) ZnCO3.
Extraction : Concentration : Froth floatation
Roasting :
ZnS + 3O2 2ZnO + 2SO2;
ZnS + 2O2 ZnSO4
2ZnSO4 2ZnO + 2SO2 + O2.
Reduction of ZnO : The oxide ore is mixed with crushed coke and heated to about 1670K in fire clay retorts (Belgian process). The crude metal obtained called Zinc spelter.
Refining : By distillation and by electrolytic method
Anode : Spelter; Cathode : Pure zinc wire; Electrolyte : Zinc sulphate.
Note :
Zinc is a volatile metal (easily vaporisable)
At ordinary temperature zinc metal is brittle but on heating at 120 – 150oC it is malleable and ductile.
Compounds of zinc
Zinc oxide ZnO : Zincite (ZnO) is also called Philospher’s wool. It is white powder, become yellow on heating and again white on cooling. It is amphoteric in nature. It is used as a white pigment under the name Zinc white or Chinese white.
Zinc Sulphate (white vitriol), ZnSO4.7H2O : It is a colourless transparent crystal highly soluble in water.
It is used as an eye-lotion and for preparing double salts. On heating it looses its molecules of water as,
ZnSO4.7H2O ZnSO4.H2O ZnSO4 ZnO + SO2 + O2