Tin
Tin is a silvery white metal at ordinary temperature.
There, however, is a grey low-temperature allotrope, the transition temperature
between the two allotropes being 13.2 °C. In practical situations, tin needs to
be kept at low temperature before the white allotrope changes to the brittle
grey allotrope.
Tin is a moderately reactive metal. It does not dissolve in dilute sulphuric acid or dilute hydrochloric acid, but it dissolves in dilute nitric acid. It also dissolves in concentrated mineral acids. With nitric acid, tin is oxidized to its +4 oxidation state, with concentrated hydrochloric acid or concentrated sulphuric acid, tin is oxidized to its +2 oxidation state.
The metal also slowly dissolves in hot concentrated alkalies, forming hydrogen gas and hydroxostannate (IV) compounds.
The metal is soft and has a fairly low melting point. For this reason, it is used for soldering electronics parts and water tubing. Frequently, the metal is alloyed with lead in order to lower the melting point even further.
Very pure tin can be obtained on eBay for reasonable price. For experiments with tin compounds, however, it is more convenient to use tin (II) chloride.
Tin can exist in the +2 and the +4 oxidation states. The metal in its +2 oxidation state is a mild reductor. Tin ions are prone to hydrolysis. Tin (II) ions already hydrolyse in plain water, such that the solution becomes turbid, due to formation of basic tin compounds and hydrous tin oxide/hydroxide. Tin (IV) ions cannot exist in the free state in water. At this oxidation state, tin has mainly acidic properties and aqueous chemistry is restricted to stannate (IV). Stannate ion also is very prone to hydrolysis and it is difficult to obtain a completely clear solution of a stannate. Stannate hydrolyses to hydrous tin (IV) oxide and hydroxide ions.
The following two compounds of tin are available for the public:
- tin (II) chloride, SnCl2
- tin (IV) oxide, SnO2
Tin
(II) chloride is a white crystalline solid, which dissolves in water very well.
It can be obtained from some photography raw chemical suppliers, but it can also
be obtained from companies, which sell materials for textile processing. Tin
(II) chloride is used in textile dyeing. Solutions of tin (II) chloride always
are turbid, unless they are strongly acidic. Tin (II) chloride is an interesting
compound, which is nice to have in a home lab. It is much more convenient for
experiments with tin than the metal.
Tin
(IV) oxide is a white powder. It is available in calcined form from ceramics and
pottery suppliers. This oxide is very inert. Even heating it in concentrated
hydrochloric acid or concentrated aqueous alkalies does not dissolve it at an
appreciable rate. Although this is a cheap compound, it is not interesting for
the home lab, due to its extreme inertness.