Lead Essay, Research Paper

subject = Chemistry

title = Lead

papers = Lead is a lustrous, silvery

metal that tarnishes in the presence of air and becomes a dull bluish

gray. Soft and flexible, it has a low melting point (327 ?C). Its chemical

symbol, Pb, is from plumbum, the Latin word for waterworks, because of

lead’s extensive use in ancient water pipes. Itsatomic number is 82; its

atomic weight is 207.19.

Lead and lead compounds can be highly toxic

when eaten or inhaled. Although lead is absorbed very slowly into the

body, its rate of excretion is even slower. Thus, with constant exposure,

lead accumulates gradually in the body. It is absorbed by the red blood

cells and circulated through the body where it becomes concentrated in

the soft tissues, especially the liver and kidneys. Lead can cause damage

in the central nervous system and apparently can damage the cells making

up the blood-brain barrier that protects the brain from many harmful chemicals.

Symptoms

of lead poisoning include loss of appetite, weakness, anemia, vomiting,

and convulsions, sometimes leading to permanent brain damage or death.

Children who ingest chips of old, lead-containing paint or are exposed

to dust from the deterioration of such paint may exhibit symptoms. Levels

of environmental lead considered nontoxic may also be involved in increased

hypertension in a significant number of persons, according to studies

released in the mid-1980s. As a result, the U.S. Centers for Disease Control

in recent years have been revising downward the levels of environmental

lead that it would consider safe. At one time, lead poisoning was common

among those who worked with lead, but such workplace hazards have been

largely curtailed.

Lead has been used by humans since ancient times.

It was used in ancient Egypt in coins, weights,

ornaments, utensils,

ceramic glazes, and solder. Lead is mentioned in the Old Testament. The

Romans

conveyed drinking water in lead pipes, some of which are still in operation.

Roman slaves

extracted and prepared the lead, describes a disease among

the slaves that was clearly lead poisoning. Because of their potential

toxicity, lead water pipes are no longer being installed. The greatest

single use of lead metal today is in the plates of storage batteries for

automobiles.

The protective oxidation layer formed by lead in contact

with such substances as air, sulfuric acid,

and fluorine makes it highly

resistant to corrosion. For this reason, lead has been used to make

drainage

pipes and lead chambers in sulfuric acid factories. It is also used as

a roofing material. The

softness and malleability of lead make it useful

for sheathing telephone and television cables. Lead is

used in solder

because of its low melting point. When combined with tin, lead forms solder

alloys

that are stronger than lead alone, with melting points lower than

those of either original metal.

Lead has the highest density of all

metals in common use, which, for example, makes it useful as a

counterweight

in the keels of ships. Because of their high density, lead bullets and

shot encounter

little air resistance and thus achieve excellent striking

power. Shot is produced by allowing molten

lead to drip down from heights

up to 38.10 m (125 ft). The drops become spherical and are

condensed

by the cooling action of the air before being collected in a tank filled

with water or oil.

Lead’s density and softness also make it highly suitable

for damping sound and vibrations. To isolate

them from vibration, heavy

machinery and even whole buildings are placed on lead blocks. Because

the

effectiveness of shielding against gamma and X rays depends largely on

the density of the shield,

lead is used in the protective shielding of

X-ray machines and nuclear reactors.

Tetraethyl lead or tetramethyl

lead (PbEt4) has often been added to gasoline to improve engine efficiency

and

reduce gasoline consumption in automobiles. Because of the toxic effect

of lead on the

environment, however, plans call for phasing out this

use. Lead azide is sensitive

to striking and is highly explosive; it

is frequently used as a detonator of explosives. Lead iodide is a

light

yellow substance that is used as a dye in such processes as coloring bronze.

It has

light-sensitive properties comparable to those of silver salts.

More

Uses

? the metal and the dioxide are used in storage batteries, cable

covering, plumbing, ammunition

? manufacture of PbEt4 – an antiknock

compound in petrol.

? environmental concern with lead poisoning, (and

cheaper unleaded petrol prices) is slowly resulting in less use of lead

in petrol

? the metal is very effective as a sound absorber, a radiation

shield around X-ray equipment and nuclear reactors

? used extensively

in paints, although recently the use of lead in paints has been drastically

curtailed to eliminate or reduce health hazards

? the oxide is used

in producing fine “crystal glass” and “flint glass” with a high refractive

index for achromatic lenses

? solder

? used by the Romans for plumbing

(the decline of the Roman empire is attributed to lead in the water supply!)

? used to contain corrosive liquids

? alloying

? cable covering

? ammunition

? shield against X-rays

? oxide used to produce crystal

glass

? insecticides