13 Physical and Chemical Properties of Tin
Tin does not occur naturally as the free element. In studying the properties of tin and its reactions, we must first examine the main source of this element which is the mineral called cassiterite or tin stone, SnO2, which is found as low grade ore in alluvial deposits in Malaysia, Bolivia and Indonesia.
In Nigeria, tin was one of the first minerals mined in 1903 in the plateau. The ore was found mainly in the valleys. Today, Nigeria provides about 4% of the world’s tin and is the seventh largest producer. About 1300 tonnes of tin is produced a year, most of which is exported.
Extraction of Tin
Tin ore, SnO2, is crushed and washed with water. This is called concentration of ore. Then it is roasted in air to remove impurities like sulphur, arsenic and antimony as volatile oxide. The product is mixed with powdered charcoal and heated to 13000C to reduce the oxide. Molten tin is then tapped off.
The tin obtained is impure. It is refined by heating it gently on a sloping surface. As molten tin flows down the surface, the impurities are exposed to air and become converted to oxide which are left behind as scum. This method of refinement gives tin with a purity of 99.9%.
Physical Properties of Tin
The physical properties of tin can be summarized below
Appearance: Silvery-white solid with luster
Relative density: Varies for different allotropes
Malleability: Very malleable metal; soft enough to be cut with a knife
Ductility: Not ductile enough to be drawn into wires
Tensile strength: Fairly strong
Melting Point: 2320C
Conductivity: Good conductor of heat and electricity.
Tin exists in three allotropic forms, which have different densities. At room temperature, tin exists as white tin. Grey tin can be converted to white tin at 13 degrees centigrade
Grey tin → white tin
Chemical Properties of Tin
Reaction with oxygen: Tin is unreactive and only combines with oxygen above 12000C. It does not corrode when exposed to the atmosphere. It also done not combine with nitrogen and carbon.
12000C
Sn(s) + O2(g) → SnO2(s)
Reaction with non-metals: Tin combines with chlorine when heated to give tin(IV) chloride.
Sn(s) + 2CI2(g) → SnCI4(s)
Reaction with Acids: Tin reacts slowly with dilute hydrochloric acid but rapidly with the concentrated acid to give tin(II) chloride.
Sn(s) + 2HCI(aq) → SnCI2(s)+H2(g)
Reaction with Dilute Tetraoxosulphate(VI) acid: Hardly any reaction is observed, but with the hot concentrated acid, sulphur(IV) oxide is evolved.
Sn(s) + 2H2SO4(aq) → SnSO4(aq) + SO2(g) + 2H2O(g)
Reaction of Tin with Trioxonitrate(V) acid: This Depends on the concentration and temperature of the acid.
Reaction with Alkalis: Tin dissolves in concentrated solutions of alkalis to give trioxostannate(IV) salts and hydrogen.
Sn(s) + 2NaOH(I) + H2O(I) → Na2SnO3(aq) + 2H2(g)
Tests for Tin(II) ions
Hydrogen sulphide Pass hydrogen sulphide into a solution of the unknown salt acidified with dilute hydrochloric acid. tin(II) ions are present if a brown precipitate which dissolves in yellow ammonium sulphide and in hot concentrated hydrochloric acid obtained.
SnCI2(aq) + H2S(g) → SnS(s) + 2HCI(aq)
Mercury(II) chloride: Add a little mercury(II) chloride solution to the unknown salt solution. On standing, the formation of a s white precipitate of mercury(1) chloride would indicate the presence of tin?(II) ions.
Aqueous ammonia: Tin(II) ions form a white precipitate of tin(II) hydroxide which is insoluble in excess aqueous ammonia.
SnCI2(aq) + 2NH4OH(aq)
→ Sn(OH)2(s) + 2NH4CI(aq)
Uses of Tin
1. The main use of tin is coating steel to prevent its corrosion. The coating can be applied by dipping steel into molten tin and rolling it or by electrolytic depositing. Tin plating is especially useful in the canning of food and drinks because tin is not poisonous.
2. Tin is used in alloys together with lead, antimony and copper. Because of its low melting point and resistance to atmospheric corrosion, tin is used in making sheet glass.
