FREE ESSAY ON PLATINUM

PLATINUM

I am a silvery metal that is as resistant to corrosion and tarnishing as gold. I am almost
as rare and consequently am the likewise highly valued and used in Jewelry. I am also
used in chemicals industry as a catalyst, in medicine as an anti-cancer drug, and in
catalytic converters for car exhausts. I have an atomic number ok 78, my atomic weight is
195.09 (when rounded 195) and a symbol of Pt. Who am I? I'm platinum of coarse!
Platinum is a member of the six transition elements in Group VIII of the periodic table
known collectively as the platinum metals (ruthenium, rhodium, palladium, osmium,
iridium, and platinum). The name is derived from the Spanish platina, meaning, silver.
The element was discovered in South America independently by Antonio de Ulloa in 1735 and
by N. Wood in 1741, but it had been in use by pre-Columbian Indians.
The platinum metals are extremely rare elements; platinum itself is the most common, with
an abundance in the Earth's crust of about a millionth of 1 percent, whereas the others
of the group have abundance's of about one ten-millionth of 1 percent. Platinum occurs in
nature as the pure metal and also in alloys with other metals of the group, principally
in the alluvial deposits of the Ural Mountains, of Columbia, and of some parts of the
western United States. In addition the element occurs in the mineral sperrylite and in
the nickel-bearing deposits of Ontario in Canada. The large-scale production of nickel
makes it feasible to recover the small amounts of platinum (only 1 part of platinum to 2
million parts of ore). The recovery of the individual platinum metals from the natural
alloys is a complex process that depends upon the distinct properties of the individual
elements, even though all members of the group are generally similar in their chemical
behavior and are quite unreactive. For example, when the natural alloy of platinum,
palladium, osmium, and rhodium is digested with aqua regia, the palladium and platinum
dissolve and are extracted as a solution of chloropalladic acid and chloroplatinic acid.
Platinum is then precipitated from this solution as ammonium chloroplatinate.
Platinum is an attractive silvery white metal with a melting point of 1,774 deg C, a
boiling point of 3,827 deg C and a density of 21.45 g/cu cm at room temperature. It has a
coefficient of thermal expansion close to that of soda-lime-silica glass and is
consequently used to make sealed electrodes in soft-glass systems.
The predominant oxidation states of platinum are +2 and +4. Platinum is chemically inert
and will not oxidize in air at any temperature. It is resistant to acids and is not
attacked by any single mineral acid but dissolves readily in aqua regia. The metal is
rapidly attacked by fused alkali oxides and by peroxides and will react with fluorine
and, at red heat, with chlorine. On heating, platinum combines directly with elemental
phosphorus, silicon, lead, arsenic, antimony, sulfur, and selenium, a fact that
influences the use of platinum laboratory equipment. In keeping with the other members of
the platinum group, the metal shows a fairly strong tendency to form complex ions. The
most common Pt (II) complexes have square planar structures and are diamagnetic.
Because of its inertness and attractive appearance, one of the major uses of platinum is
in the manufacture of jewelry. Gold-platinum alloys, referred to as white gold, are
widely used in dentistry and in the making of jewelry. Platinum and its alloys are used
in the manufacture of crucibles and evaporating dishes for chemical analyses. Other
applications include the formation of thermocouple wires, electrical contacts,
corrosion-resistant apparatus, and the manufacture of platinum resistance thermometers
used in the temperature control of furnaces. The alloy, consisting of 76.7% platinum and
23.3% cobalt by weight, forms an extremely powerful magnet. More recent applications of
the metal involve the coating of missile cones and jet-engine fuel nozzles.
Along with palladium, the metal absorbs large volumes of hydrogen, retaining it at
ordinary temperatures but desorbing it at red heat. The fact that the absorbed hydrogen
is extremely reactive suggests that it is present either as atomic hydrogen or as a very
reactive platinum-hydrogen compound or complex. In finely divided form platinum is an
excellent catalyst; about half of the annual production of the metal serves this purpose,
most of it in the petrochemical industry. It is also used as a catalyst in the contact
process for the manufacture of sulfuric acid from sulfur dioxide and oxygen. There is
much current interest in the application of the metal as a catalyst in fuel cells and in
catalytic converters as antipollution devices for automobiles. In the latter instance a
suitable form of platinum will catalyze the oxidation of carbon monoxide to carbon
dioxide and will convert nitric oxide to nitrogen and water. Fine platinum wire glows
when placed in methyl alcohol vapor, where it acts as a catalyst, converting the alcohol
to formaldehyde. This effect is used commercially to produce cigarette lighters and hand
warmers.
The price of platinum has varied widely relative to the price of gold. Although it is
slightly more valuable today, it was once used as a gold adulterant.
Bibliography
Grolier 1996 computer encyclopedia
American Desk Encyclopedia copyright in 1998
www.britanica.com