d Block Elements : Zinc and its Compounds

 

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  \underrightarrow { \quad 1200\quad K\quad }  2ZnO + 2SO2;

ZnS + 2O2  \underrightarrow { \quad \Delta \quad } ZnSO4                         

2ZnSO4  \underrightarrow { \quad \Delta \quad }  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,

ZnSO4.7H2 \underrightarrow { \quad 375\quad K\quad } ZnSO4.H2O  \underrightarrow { \quad 725\quad K\quad } ZnSO4  \underrightarrow { \quad 1075\quad K\quad } ZnO + SO2 + O2

 

d Block Elements : Lanthanides