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Tin
Symbol Sn, metallic element that has been used by people
since ancient times. Tin is in group 14 (or IVa) of the periodic table. The atomic number
of tin is 50.
Tin has been found in the tombs
of ancient Egyptians and was exported to Europe in large quantities from Cornwall,
England, during the Roman period. The ancient Egyptians considered tin and lead different
forms of the same metal.
II.
Properties and Occurrence
Tin is highly ductile and
malleable at a temperature of 100° C (212° F). It is attacked by strong acids.
Ordinarily a silver-white metal, at temperatures below 13° C (55° F) it often changes
into an allotropic (distinctly different) form known as gray tin, which is
an amorphous, grayish powder with a specific gravity of 5.75. Because of the mottled
appearance of tin objects undergoing this decomposition, the action is commonly referred
to as tin disease or tin pest. Ordinary bar tin, when bent, issues a crackling sound
called tin cry, caused by the friction of the tin crystals.
Tin ranks 49th in abundance of
the elements in the earth's crust. Ordinary tin melts at about 232° C (about 450° F),
boils at about 2260° C (about 4100° F), and has a specific gravity of 7.28. The atomic
weight of tin is 118.69.
The principal ore of tin is the
mineral cassiterite (or tinstone), SnO2, found
abundantly in Cornwall, England and in Germany, the Malay Peninsula, Bolivia, Brazil, and
Australia. In the United States workable deposits of tin have been found only on Alaska's
Seward Peninsula. In the extraction of tin, the ore is first ground and washed to remove
all impurities and then roasted to oxidize the sulfides of iron and copper. After a second
washing, the ore is reduced by carbon in a reverberatory furnace; the molten tin that
collects on the bottom is drawn off and molded into blocks known as block tin. In this
form, the tin is re-smelted at low temperatures; the impurities form an insoluble mass.
Tin may also be purified by electrolysis.
III.
Compounds
Tin forms stannic acid, H2SnO
4, when heated in air or oxygen at high temperatures. It dissolves in hydrochloric
acid to form stannous chloride, SnCl2, and in aqua regia to form stannic
chloride, SnCl4, and it reacts with sodium hydroxide solution to form sodium
stannite and hydrogen gas. In cold and very dilute nitric acid, tin dissolves to form
stannous nitrate and ammonium nitrate; in concentrated nitric acid, it produces
metastannic acid, H2SnO3. Stannous sulfide, SnS, is yielded as a
dark brown precipitate by the action of hydrogen sulfide on a solution of stannous
chloride. Stannic sulfide, SnS2, is produced by passing hydrogen sulfide
through a solution of stannic salt. The two hydroxides of tin, Sn(OH)2 and
Sn(OH)4, are produced by adding a soluble hydroxide to solutions of stannous
and stannic salts. Stannous oxide, SnO, a black insoluble powder, is obtained by heating
stannous oxalate in the absence of air. In the presence of air, stannous oxide burns to
form the dioxide, or stannic oxide, SnO2, a white insoluble solid. The dioxide
may also be prepared by heating stannic acid or by heating tin metal in air at high
temperatures.
IV. Uses
Tin is a widely sought metal and
is used in hundreds of industrial processes throughout the world. In the form of tinplate, Pewter Sheets or Jewelers model sheets (JMS), it is
used as a protective coating for copper vessels, various metals used in the manufacture of
tin cans, and similar articles. Tin is important in the production of the common alloys
bronze (tin and copper), solder (tin and lead), and
type metal (tin, lead, and antimony) . It is also used as an alloy with titanium in the
aerospace industry and as an ingredient in some insecticides. Stannic sulfide, known also
as mosaic gold, is used in powdered form for bronzing articles made of plaster of Paris or
wood.
The United States imports more
than one-fifth of the average annual world production of tin. Most of the world's tin is
produced by Malaysia, Brazil, Indonesia, Thailand, Bolivia, and Australia.
Information
from
"Tin," Microsoft® Encarta® Online Encyclopedia 2000
http://encarta.msn.com © 1997-2000 Microsoft Corporation. All rights reserved.
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Specifications:
Tin (Sn)
Atomic
Number
50
Atomic
Weight
118.69
Boiling
Point
2603°C
Melting
Point
232°C
Specific
Gravity
7.3
Electron
Configuration
Kr/4D10,5S2P2
Electro-negativity
1.96
Heat of
Vaporization
295.8
Heat of
Fusion
7.029
Electrical
Conductivity
0.0917
Thermal
Conductivity
0.666
Specific
Heat0
.227
First Ion
Potential
7.344
Covalent
Radius
1.41
Atomic
Radius
1.72
Atomic
Volume
16.3
Oxidation
States
4,2
