Tin 19/12/07 Written By Elisha Lai Mr. Estey
B. Characteristics/Properties: Tin is a malleable, ductile, highly crystalline, silvery-white metal whose crystal structure causes a strange screeching sound known as the "tin cry" when a bar of tin is bent (caused by crystals breaking). This metal resists corrosion from distilled sea and soft tap water, but can be attacked by strong acids, alkalis, and by acid salts. Tin acts as a catalyst when oxygen is in solution and helps accelerate chemical attack. Tin forms the dioxide SnO2 when it is heated in the presence of air. SnO 2, in turn, is feebly acidic and forms stannate (SnO 3-2) salts with basic oxides. Tin can be highly polished and is used as a protective coat for other metals in order to prevent corrosion or other chemical action. This metal combines directly with chlorine and oxygen and displaces hydrogen from dilute acids. Tin is malleable at ordinary temperatures but is brittle when it is heated. Tin has a melting point of 231.9681°C, boiling point of 2270°C, specific gravity (gray) of 5.75 or (white) 7.31, with a valence of 2 or 4. The density is 6.99 g/cm³. The hardness is about 1.5 on the Mohs Hardness Scale. The streak of tin is white. The luster of tin is metallic. When a bar of tin is bent, the crystals break, producing a characteristic 'tin cry'. Two or three allotropic forms of tin exist. Gray or α tin has a cubic structure. Upon warming, at 13.2°C gray tin changes to white or β tin, which has a tetragonal structure. This transition from the α to the β form is termed the tin pest. A γ form may exist between 161°C and the melting point. When tin is cooled below 13.2°C, it slowly changes from the white form to the gray form, although the transition is affected by impurities such as zinc or aluminum and can be prevented if small amounts of bismuth or antimony are present. Tin is resistant to attack by sea, distilled, or soft tap water, but it will corrode in strong acids, alkalis, and acid salts. The presence of oxygen in a solution accelerates the rate of corrosion. C. Places Where It Is Found: About 35 countries mine tin throughout the world like Malaysia, Bolivia, Indonesia, Zaire, Thailand, Vietnam and Nigeria. Nearly every continent has an important tin-
mining country. Tin is produced by reducing the ore with coal in a reverberatory furnace. This metal is a relatively scarce element with an abundance in the Earth's crust of about 2 ppm, compared with 94 ppm for zinc, 63 ppm for copper, and 12 ppm for lead. Most of the world's tin is produced from placer deposits; at least one-half comes from Southeast Asia. The only mineral of commercial importance as a source of tin is cassiterite (SnO2), although small quantities of tin are recovered from complex sulfides such as stannite, cylindrite, franckeite, canfieldite, and teallite. Secondary, or scrap, tin is also an important source of the metal. D. Chemical Formula: [Kr] 4d10 5s2 5p2 E. Uses: Tin is used to coat other metals to prevent corrosion. Tin plate over steel is use to make cans for food. Some of the important alloys of tin are soft solder, fusible metal, type metal, bronze, pewter, Babbitt metal, bell metal, die casting alloy, White metal, and phosphor bronze. The chloride SnCl路H2O is used as a reducing agent and as a mordant for printing calico. Tin salts may be sprayed onto glass to produce electrically conductive coatings. Molten tin is used to float molten glass to produce window glass. Crystalline tin-niobium alloys are superconductive at very low temperatures. F. Extra Information: History Tin was known to the ancients and is mentioned in the Old Testament. Early metal workers found it too soft for most purposes but mixed with copper it gives the alloy bronze, of Bronze Age fame. Tin is one of the elements which has an alchemical symbol, shown below (alchemy is an ancient pursuit concerned with, for instance, the transformation of other metals into gold).