PTL:Lead

From ChemEd Collaborative

Lead

Lead, a metal, is the heaviest element of Group IVA and is in the 6th period. Other members of the group are carbon (C), silicon (Si), germanium (Ge), and tin (Sn).

1 Discovered
2 Name
3 Characteristics
4 Found
5 Prepared
6 Reactions
7 Uses
8 Emission Spectra

Discovered

It is an element known to the ancient world and was produced as the metal as early as 1200 B.C.

Name

Its name comes from the Anglo-Saxon, but the symbol Pb is from the Latin word for the element, plumbum.

Characteristics

It exists as Pb(II) and Pb(IV) in its compounds.

The metal is bluish-white and is very soft, malleable, and ductile. It has a low electrical conductivity. It is the densest element of Group IVA,

Pb (11.3 g/cm3) > Sn (7.3) > Ge (5.3) > Si (2.3) > C (2.3)

but it is much less dense than the transition elements of the 6th period. (See Platinum, for example.) In the solid state, the metal has a face-centered cubic structure.

Found

The element is by far the most abundant of the heavier elements. Indeed, it is more than 10 times more abundant than either germanium or tin, but about 10 times less abundant than carbon. This abundance is related to the fact that three of the four naturally occurring isotopes of lead (206, 207, and 208) are the stable end products of natural radioactive series.

Prepared

Lead is obtained chiefly from the mineral galena, PbS. However, it is also found as anglesite (PbSO₄) and cerussite (PbCO₃). World production is in the range of 3 million tons, with most from the Soviet Union, U.S., Australia, and Canada.

The lead is obtained from galena by "roasting" or heating in air to give PbO.

PbS + O₂ PbO + SO₂

(The SO₂ from this and similar processes has been a source of some the "acid rain" problems around the world.) The lead(II) oxide is then reduced with coke or CO.

PbO + C Pb + CO

PbO + CO Pb + CO₂

Minerals Containing Lead
Galena	Anglesite	Cerussite

Reactions

Finely divided Pb powder will burn spontaneously in air. However, the bulk metal usually has a thin coating of insoluble oxide, carbonate, or sulfate, which protects the surface and renders the lead quite inert . This resistance to corrosion is the reason the Romans used it to carry water and for drains, uses that gave rise to the English word "plumbing".

If lead is heated in air, a film of yellow PbO forms on the surface of the molten lead.

2 Pb(s) + O₂(g) 2 PbO(s)

[[Aqueous HCl]] reacts slowly with the metal, and a film of insoluble PbCl₂ soon covers the surface.

Pb(s) + 2 HCl(aq) PbCl₂(s) + H₂(g)

Nitric acid, though, does react with the metal to give nitrogen oxides and lead(II) nitrate.

Uses

Lead is used in solder for electrical connections and to join copper pipe for water distribution; it is used to make lead shot; it is also used as the electrode in lead-acid storage batteries

Lead oxide is used to make lead glass which is the glass used in fine crystal

Almost half of the lead produced is used in [storage batteries], where an alloy of 91% Pb and 9% Sb supports a spongy lead anode

Pb(s) + SO₄^2-(aq) PbSO₄(s) + 2e-

E° = +0.356 V

and lead(IV) oxide as the cathode.

PbO₂(s) + 4 H+(aq) + SO₂^2-(aq) + 2e- PbSO₄(s) + 2 H₂O

E° = +1.685 V

Over 80% of the lead used in batteries is recovered and recycled.

Lead melts at only 327°C. When mixed with other metals to give an alloy, the melting temperature is even lower, so these mixtures are used as [solders]. Virtually all common solders contain Sn and Pb in varying amounts with smaller amounts of Cd, Bi, Ag, and Sb. For example, common electronic solder is 63% Sn and 37% Pb.

Other lead-containing alloys are used in type metal (Pb, Sb, and Sn) and in lead shot for shotgun shells.

Lead is toxic to humans in all forms. The most common signs of lead poisoning or "plumbism" are gastrointestinal: anorexia, nausea, vomiting, diarrhea, and constipation. There are also reproductive effects such as decreased fertility and increased abortion.

The severe health effects of lead compounds has led to major changes in our economy. Until quite recently, one of the major uses of lead was in the form of tetraethyllead [Pb(C₂H₅)₄] as an anti-knock compound in gasoline. This has now been phased out in the U.S.

Yellow lead chromate (PbCrO₄) and "red lead" (Pb₃O₄), as well as white lead titanate (PbTiO₃), have been widely used as paint pigments, but their use is declining as well owing to the health effects of lead compounds.

In the presence of air lead dissolves in organic acids such as acetic acid to give soluble salts.

Pb(s) + ½ O₂(g) + HC₂H₃O₂(aq) Pb(C₂H₃O₂)₂(aq) + H₂O

Therefore, lead containers cannot be used to store wine, fruit juice, or similar liquids. This led to the theory that the Roman empire fell because so many were poisoned from drinking wine and juices from lead vessels. Nonetheless, you should never drink soft drinks, wine, or fruit juice from a ceramic cup that has been covered with a lead-containing glaze.

Finally, lead oxide is used to make "lead glass", the [glass] used in fine crystal. This glass has a high index of refraction and so sparkles and refracts light into its colors. Objects of art made from glass can cost many hundreds of dollars.