Tin

 

Tin

Chemical formula	Sn
Atomic Number	50
OTP appearance	grey solid
Molar Mass(g/mol)	118.7
Density(g/cc)	7.365
Melting Point(°C)	231.93
Boiling Point(°C)	2602
Coefficient of Thermal Expansion(×10-6 °C-1)	23.8
NFPA 704	0 1 0

Uses

Primary

• as a component of bronze, brass and pewter.
• as a component of solder

Secondary

• tin is a useful structural material where its malleable nature is used, such as hinges or crimpable fasteners

Natural Sources

• Elemental tin does not occur naturally
• -oxide occurrs naturally as cassiterite

Hazards

• Virtually all organotin compounds are highly toxic
• At temperatures below 14°C, tin undergoes an allotropic change which changes the tin from a metallic form to a nonmetallic form. This is called "tin blight" or "tin pest". This process slowly reverses above 14°C and is rapidly reversed above 100°C.

Character

• Tin has two important allotropes:
  • α- or "grey" tin which is grey, brittle, and nonmetallic.
  • β- or "white" tin which is silvery, ductile and metallic.
• At 13.2 °C and below, pure Β tin transforms to α-tin
• At 100°C and above α-tin reverts to Β-tin.

Production

Extraction

• Carbothermic reduction of cassiterite

Reduction of tin with carbon is not an easy process since the free energies of reduction are unfavorable.

SnO₂ + C → Sn + CO₂ΔH=+125.2 kJ

However, reduction with carbon monoxide is considerably less unfavorable. For the reaction

SnO₂ + CO → SnO + CO₂ΔH=+5.5 kJ // First oxygen

SnO + CO → Sn + CO₂ΔH=-0.3 kJ // Second oxygen

SnO₂ + 2 CO → 2 CO₂ + SnΔH=+5.2kJ // Net

Storage

• stacked as ingots, keeping the temperature above 14°C

See Also

• Smelting Tin at Geevor Museum
• An Analysis of the Process of Smelting Tin, The Bulletin of Peak District Mines Historical Society Vol 13 No 2 Winter 1996