Tin can combine with other atoms in two ways to form several tin compounds
- It can covalently share the two p electrons (5p2) in the outermost shell of its atom to form tin(II) compounds. These compounds dissolve in water to give tin(II) ions, Sn2.
- It can also covalently share all the four electrons (5s25p2) in the outermost shell of its atom.
Tin(II) compounds are strong reducing agents since they can be readily oxidized to tin(IV) compounds. Here are 6 important tin compounds used in chemical and industrial production processes.
Tin(II) oxide, SnO, can be made by heating tin(II) ethanedioate or tin(II) hydroxide in an inert atmosphere.
SnC2O4·2H2O → SnO + CO2 + CO + 2 H2O
It is grey solid which oxidizes readily to tin(IV) oxide when heated in air.
2 SnO + O2 → 2 SnO2
Tin(II) oxide is amphoteric, giving tin(II) salts when it reacts with acids, and tetrahydroxostannates(II) when it reacts with alkalis.
Sn(OH2)32+ and Sn(OH)(OH2)2+
Tin(IV) oxide, SnO2, occurs naturally as cassiterite and can be made by heating tin strongly in air, by dissolving tin in concentrated trioxonitrate (V) acid or by hydrolyzing tin(IV) chloride.
If tin (IV) oxide it freshly prepared, it is amphoteric and dissolves both in concentrated acids and alkalis.
SnO2 + 2 H2SO4 → Sn(SO4)2 + 2 H2O
Tin(IV) oxide is used industrially to make white enamel and tiles.
When tin(II) salts are added to an alkali, tin(II) hydroxide is precipitated.
Tin(II) hydroxide is amphoteric and reacts with both alkalis and acids as shown. This compound can also be gotten by this reaction in an aprotic solvent
2 Me3SnOH + SnCl2 → Sn(OH)2 + 2 Me3SnCl
Tin(II) chloride, is prepared by heating tin in a stream of dry hydrogen chloride gas or by dissolving tin in concentrated hydrochloric acid. when acid is used, the salt is obtained as a dehydrate.
Anhydrous tin(II) chloride is a covalent white solid. Both the anhydrous chloride and he dehydrate dissolve readily in water. This solution soon turns milky due to hydrolysis and the formation of a basic salt.
SnCl2 (aq) + H2O (l) ⇌ Sn(OH)Cl (s) + HCl (aq)
Hydrolysis of the chloride can be prevented by adding hydrochloric acid. a piece of tin is also added to this solution to prevent aerial oxidation to tin (IV) chloride.
Tin (II) chloride reduces iron(III) salts to iron(II) salts, copper(II) salts to copper(I) salt, and mercury(II) salt to the metal.
SnCl2 (aq) + 2 FeCl3 (aq) → SnCl4 (aq) + 2 FeCl2 (aq)
Tin(IV) chloride, SnCI4, can be made by passing dry chlorine over heated tin. It is a colourless covalent liquid that fumes in moist air, due to hydrolysis, to form tin(IV) oxide. This compound was discovered by Andreas Libavius in the 16th century and was then known as Spiritus fumans libavii.
Sn + 2 Cl2 → SnCl4
SnCl4 + 4H2O ⇄ Sn(OH)4 + 4HCl
Tin(IV) hydride is unstable and decomposes at room temperature. It is an organotin compound and can be prepared by reacting tin(IV) chloride and lithium tetrahydridoaluminate(III) at low temperatures. This compound is highly toxic and must be handled with care.
SnCl4 + Li[AlH4] → SnH4 + LiCl + AlCl3
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