Platinum - chemistry.

Platinum - chemistry. I INTRODUCTION Platinum, symbol Pt, relatively rare, chemically inert metallic element that is more valuable than gold. The atomic number of platinum is 78. The element is one of the transition elements in group 10 (or VIIIb) of the periodic table (see Periodic Law). Platinum is the most important of the group of elements called the platinum metals, the other members of which are ruthenium, rhodium, palladium, osmium, and iridium. Impure platinum was used thousands of years ago both in Europe and in South America. The separation of the other platinum metals from platinum and from each other was accomplished in the early 19th century. The element's silvery-white color inspired its name, which comes from the Spanish and Italian word platina, "silver." II PROPERTIES AND OCCURRENCE Platinum has a hardness of 4.3. It has a high fusing point, is malleable and ductile, expands slightly upon heating, and has high electrical resistance. Chemically the metal is relatively inert and resists attack by air, water, single acids, and ordinary reagents. It dissolves slowly in aqua regia, forming chloroplatinic acid (H2PtCl6); is attacked by halogens; and combines upon ignition with sodium hydroxide, sodium nitrate, or sodium cyanide. Platinum melts at about 1768°C (about 3214°F), boils at about 3825°C (about 6917°F), and has a specific gravity of about 21.45. The atomic weight of platinum is 195.08. Platinum ranks about 72nd in natural abundance among the elements in crustal rock. Except for the mineral sperrylite, which is platinum arsenide and is found only sparingly in a few localities, platinum occurs in the metallic state, often alloyed with other platinum metals. Nuggets of the metal weighing up to 9.5 kg (21 lb) have been found. III USES Because of its chemical inertness and high fusing point, platinum is valuable for laboratory apparatus, such as crucibles, tongs, funnels, combustion boats, and evaporating dishes. Small amounts of iridium are usually added to increase its hardness and durability. Platinum is also used for contact points in electrical apparatus and in instruments used for measuring high temperatures. Finely divided platinum in the form of platinum sponge or platinum black is used extensively as a catalyst in the chemical industry. A considerable amount of the platinum used in the United States goes into jewelry, in which it is often alloyed with gold. It is also used for dental fillings. Platinum is mined all over the world; in the early 2000s South Africa and Russia were the leading producers. Canada, with mines in Ontario, where platinum is associated with nickel ore, ranked third in world production. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.