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Tin, both a very practical metal and a troublesome metal for the refiner. Dissolved in hydrochloric acid it forms stannous chloride that is used for detecting gold in acid solutions while in solutions with nitric acid it forms a gel, metastannic acid that is almost impossible to filter.
While studying tin, its salts and Amphoterism of metals I have these notes in one of my note books
Stannic salt, adding a caustic alkali to a solution of stannic salt will form a voluminous gelatinous white precipitant. example: SnCl4 + 4 OH --> 4Cl + Sn(OH)4 this precipitant if dried in air forms Sn(OH)4, but if dried over sulfuric acid would form H2SnO3 (meta stannic acid).
Sn(OH)4 or H2SnO3 precipitate dissolves readily in excess of alkali hydroxide, forming salts which are not derived from either of the above compounds but from H2[Sn(OH)6] H2SnO3 + 2KOH --> K2[SN(OH)4]
(the hydroxide also dissolves in ammonia solution, but only in the absence of ammonium salts).
From another note: concentrated nitric acid and tin converts to a white insoluble powder metastannic acid, which is a hydrated oxide of tin, H2SnO4 or H2SnO3 Sn + 4HNO3 --> H2SnO3 + H2O + 4NO2 Metastannic acid is different from stannic acid because it is insoluble in acids. and with alkalies it forms salts like K2Sn5O11 or Na2Sn5O11
Tin seems to be a very complicated metal to study.
Compounds and chemical reactions of tin
Tin can be dissolved in hydrochloric acid, forming stannous chloride (tin(II) chloride).
Stannous chloride reacts with oxygen from the air to form stannous oxychloride, Template:Sn(O(OH),Cl.
Stannous oxychloride decomposes at 120C to SnCl4 (stannic chloride) and Template:SnO2.
Tin can also be dissolved in sodium hydroxide mixed with strong hydrogen peroxide. Probably by oxidize metallic tin and the oxide reacts to form sodium stannate which is soluble in strong sodium hydroxide.
Uses for tin in refining
(Main article : Testing for precious metals with stannous chloride)
Mostly tin is a nuisance in refining, forming gelatinous gray gunk that makes solutions impossible to filter or turning dissolved gold into colloidal solution. The one use tin has in refining is in testing, as stannous chloride reacts with most precious metals.
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