Pigments (Short Note) 2nd Year Chemistry Notes

Definition

Pigments are the substances which are used to give the proper colour to paints. 


Types of Pigments

Lead forms various types of pigments. Some of them are given below. 
1. White lead Pigment 
2. Red lead Pigment 
3. Chrome Yellow Pigment 
4. Chrome Red Pigment 
5. Turner's Yellow Pigment 

1. White Lead Pigment 
White lead Pigment is a basic lead carbonate. 

Molecular Formula 
[2PbCO3. Pb(OH)2] or [Pb3(OH)2.(CO3)2] 

Colour 
This lead pigment is white in colour. 

Properties 
The white colour gradually darken due to the formation of Pbs with Atmospheric H2S. It is also poisonous. 

2. Red Lead Pigment (Sandhur) 

Molecular Formula 
Pb3O4 - Triplumbic Tetra Oxide 
2PbO.PbO2 - Lead-Sesqui Oxide 

Colour 
It is used as red coloured pigment, which varies from orange red to brick red dur to particle size and impurities. 

Properties 
It is soluble in water but soluble in acids. 

3. Chrome Yellow Pigment 

Molecular Formula 
PbCrO4 - Lead Chromate 
It occurs in nature as crocoite. 

Colour 
It is used as yellow coloured pigment. 

Properties 
It is insoluble in water but soluble in nitric acid and caustic alkalis. 

4. Chrome Red Pigment 

Molecular Formula 
PbCrO4.PbO - Basic Lead Chromate 
Pb2CrO5 - Basic Lead Chromate 

Colour 
It is used as dark red pigment in paints. 

5. Truner's Yellow Pigment 

Molecular Formula 
PbCl2.4PbO 


Other Pigments

Except above pigments, yellow lead monoxide (massicot) and red lead monoxide (litharge or Murda-sang) are also used in paints