Zinc Sulphate or White Vitriol (ZnSO4.7H2O)

Zinc sulphate heptahydrate is commonly known as white vitriol. It is obtained by dissolving zinc, zinc oxide, zinc hydroxide, zinc carbonated in dilute H2SO4. The solution of zinc sulphate on crystallization gives colorless crystal of ZnSO4 7H2O.

 

            Zn + H2SO4      →          ZnSO4 + H2O

            Zn + H2SO4         →        ZnSO4 + H2O

            Zn (OH)2 + H2SO4      →      ZnSO4 + 2H2O

            Zn CO3 + H2SO4    →     ZnSO4 + H2O + CO2

            ZnSO4 (aq)    crystallization    →   ZnSO4 7H2O

                                                                                    White Vitriol

 

In large, ZnSO4 is obtained by heating ZnS in air below 9000c

            ZnS + O2         below 900   →           ZnSO4

 

Properties:

 

1. (Crystalline) ZnSO4 7H2O is colorless crystalline solid white anhydrous ZnSO4 7H2O is an efflorescent solid.

2. ZnSO4 7H2O is an efflorescent solid and effloresces when exposed in air to give monohydrate. The last H2O molecule is lost at 3000c.

            ZnSO4 7H2O               exposed in air  →        ZnSO4 H2O + 6H2O

            ZnSO4 H2O                 300       →             2Zn + SO2   + H2O

 

The anhydrous zinc Sulphate on heating above 9000c decomposes forming ZnO.

            2ZnSO4 (aq)                above 900    →          2ZnO + SO2 + O2

 

3. Action of NaOH:-

 

ZnSO4 solution gives off white ppt of Zn (OH)2 with NaOH which dissolves on adding excess NaOH forming sod. Zincate.

            ZnSO4 + 2NaOH                  →              Zn(OH)2 + Na2SO4

Zn(OH)2 + 2NaOH                →             Na2ZnO2 + 2H2O

 

Uses:

1. It is used in medicine

2. It is used as mordant in dying.

 

3. It is used as electrolyte in electroplating of zinc.

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