Lead

Lead, Pb, is a metallic main group element, found in Group IVb of the periodic table.

Atomic Number : 82
Relative Atomic Mass : 207.2

Discovery

Lead was known to the Egyptians 3000 years ago, and was used by the Romans for water pipes.

Occurrence

Lead is known to occur in elemental form in some locations. However, the principal ores are

Gelena, PbS,
Cerussite, PbCO3,
Anglesite, PbSO4,
Crocoisite, PbCrO4,
Wulfenite, PbMoO4,
Pyromorphite, PbCl2.3Pb(PO4)2, and
Matlockite, PbCl2.

Extraction

Preparation

Manufacture

Lead is manufactured by smelting the gelena in admixture with sand, limestone and iron ore.


	3 PbS   +   3 O2   ==>   2 PbO   +   2 SO2	

	  PbS   +   2 O2    ==>   PbSO4	

	PbSO4   +   SiO2    ==>   PbSiO3   +   2 SO3

The resulting sinter is mixed with coke and discharged into the top of a blast furnace, while air is forced through the bottom.


	2 C   +   O2    ==>   2 CO	
	
	PbO   +   CO    ==>   Pb   +   CO2	

	PbSiO3  +  CaO  +  CO  ==>  Pb +  CaSiO3  +   CO2

The products of the smelting, lead and slag are removed at the bottom of the furnace.

Properties

Lead is a soft bluish-gray lustrous metal, which can be easily shaped under pressure into rods and pipes and rolled into sheets.

Lead is stable in dry air, but quickly tarnished in moist air, due to the formation of a film of oxide.

Lead is rendered much harder when it contains trace amounts of different impurities, including antimony, arsenic, zinc, and copper.

Reactions

Lead is not attacked by Sulphuric Acid, H2SO4.

Lead is dissolved by concentrated nitric acid and by warm solutions of the dilute acid.

Lead is dissolved by organic acids, including acetic acid.

Uses

Lead is widely used

in the arts, as it can be easily worked and molded,
for pipes to carry water, although this use is now diminishing due to its toxicity,
in a range of alloys including
- Plumbers Alloy (33% lead and 66% tin),
- Pewter (75% tin and 25% lead), and
- Type Metal (75% lead, 5% tin and 20% antimony),
in the chemical industry for tanks and pipe work, as it is resistant to attack by sulphuric acid, and
in roofing in the form of the sheet metal.

Detection and Analysis

Lead is identified by the characteristic precipitate of lead chloride which precipitates out on the addition of hydrochloric acid to a solution of its salts. The precipitate is soluble in hot solution and recrystallises as fine white needles.

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