Lead pigments

Various compounds of lead especially oxides of lead are used as pigments in paints. This presentation is a lesson about preparation, properties and uses of lead pigments.

1. XII CHEMISTRY CHAPTER 4 MS. SIDRA JAVED Lead Pigments

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

3. Lead Pigments 1. White lead Pigment 2. Red lead Pigment (Sandhur) 3. Chrome Yellow Pigment 4. Chrome Red Pigment 5. Turner's Yellow Pigment 6. Yellow Lead monoxide (Massicot) 7. Red lead monoxide (Litharge or Murda sang)

4. White lead Pigment Chemical Name: Basic Lead Carbonate Chemical formula: [2PbCO 3 .Pb(OH) 2 ] or Pb 3 (OH) 2 (CO 3 ) 2 Used in white paints as a pigment White color darkens due to formation of PbS Toxic in nature It is now replaced by Titanium oxide due to toxicity

5. White Lead Pigment - Preparation Chamber process or Dutch process: Strips of lead are placed in Chambers (earthenware) Mixture of acetic acid and steam is passed for 2-3 days until lead is corroded 2Pb+2CH 3 COOH+2H 2 O →[Pb(OH) 2 Pb(CH 3 COO) 2 ] + 2 H 2

6. A mixture of CO 2 and acetic acid vapors is passed through the corroded lead for 3-4 weeks White lead is formed which is then scratched, dried and packed. 3[Pb(OH) 2 .Pb(CH 3 COO) 2 +2H 2 O+2CO 2 → 2[2PbCO 3 .Pb(OH) 2 ] + 6CH 3 COOH

7. A better white lead is prepared by Passing CO 2 into the suspension of Lead oxide in water containing little quantity of Lead acetate 2PbO + 2CO 2 + 2H 2 O + Pb(CH 3 COO) 2 → [2PbCO 3 .Pb(OH) 2 ] + 2CH 3 COOH + O 2

8. Red Lead Pigment (Sandhur) Chemical Formulae & Chemical name: Pb 3 O 4 - Triplumbic Tetraoxide (2PbO.PbO 2 ) - Lead sesqui oxide Color: Red Used to prepare paints of different shades from Orange red to brick red Insoluble in water Soluble in acids

9. Red Lead pigment - Preparation Prepared by heating PbO in a revolving furnace with excess of air about 450 C 6PbO + O 2 2Pb 3 O 4 450 C

10. Chrome Yellow Pigment Chemical Formula: PbCrO 4 Chemical Name: Lead Chromate Color: Yellow Occur in nature as Crocite Insoluble in water Soluble in nitric acid and cuastic alkalis

11. Chrome Yellow Pigment - Preparation Adding solution of Potassium Chromate K 2 CrO 4 to solution of Lead nitrate Pb(NO 3 ) 2 Action of Potassium Chromate on Lead acetate Pb(NO 3 ) 2 + K 2 CrO 4 → PbCrO 4 + 2KNO 3 Pb(CH 3 COO) 2 + K 2 CrO 4 → PbCrO 4 + 2CH 3 COOK

12. Chrome Red Pigment Chemical formula: PbCrO 4 .PbO or Pb 2 CrO 3 Chemical name: Basic Lead Chromate Color: Dark Red Used as red pigment

13. Chrome Red Pigment - Preparation 2PbCrO 4 + 2NaOH → Na 2 CrO 4 + Pb 2 CrO 3 + H 2 O Prepared by digesting Lead Chromate with NaOH

14. Turner’s yellow Pigment Chemical formula: PbCl 2 .4PbO Prepared by boiling NaCl solution with Litharge i.e. Lead Monoxide 5PbO + H 2 O + 2NaCl → 2NaOH + PbCl 2 .4PbO

15. Yellow Lead monoxide (Massicot) Red Lead Monoxide (Litharge)

16. End of Lesson