XII Chemistry BIEK Topic - Pigments (Short Note)

Pigments (Short Note)
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.