Chapter: 11th 12th std standard Class Organic Inorganic Physical Chemistry Higher secondary school College Notes

Zinc carbonate and Purple of cassius: Preparation, Properties and Uses

Zinc carbonate occurs in nature as calamine. Purple of cassius is only a form of colloidal gold. It is purple or red in colour and after the name of Cassius who discovered it.

Zinc carbonate (ZnCO3)

Zinc carbonate occurs in nature as calamine.

Preparation

When NaHCO3 is added to Zinc sulphate solution, ZnCO3 is obtained.

ZnSO4 + 2NaHCO3 � ZnCO3 + Na2SO4 + H2O + CO2�

Properties

Physical properties

It is a white powder, insoluble in water.

Chemical properties

i) Action of Heat

On heating at 300 o C , Zinc carbonate decomposes into Zinc oxide and

Uses

ZnCO3 ⎯300⎯� ZnO + CO2 ⎯ o C

i) It is used in making ointment for curing skin diseases.

ii) It is used in the preparation of cosmetics.

iii) It is used a pigment for rubber.

Purple of cassius

Purple of cassius is only a form of colloidal gold. It is purple or red in colour and after the name of Cassius who discovered it.

Preparation

It is prepared by mixing very dilute solution of gold chloride with stannous chloride solution.

2AuCl3 + 3 SnCl2 � 2Au� + 3SnCl4

The gold thus precipitated is adsorbed by stannic hydroxide formed by the hydrolysis of SnCl4.

SnCl4 + 4H2O � Sn(OH)4 + 4HCl

Uses

It is used in making ruby-red glass and high class pottery.

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11th 12th std standard Class Organic Inorganic Physical Chemistry Higher secondary school College Notes : Zinc carbonate and Purple of cassius: Preparation, Properties and Uses |