Monday, 18 July 2011

Ammonium Hexachlorostannate - Pink Salt - 50 g

Chemical formula: (NH4)2SnCl6

Synonyms: pink salt, ammonium hexachlorostannate (IV)

Amount: 50 g

Appearance and odour: off-white crystals without appreciable odour.

Grade: Technical

Packaging: professional wide necked, white HDPE bottle with blue conical seal cap and tamper ring. Labelled. Bottle and cap are UN approved and reusable.

Description and uses: so called ‘pink salt’ because it was once used as a dye mordant for vivid pink colours with dyes like Madder and Cocheneal.

For chemists ammonium hexachlorostannate is a tin (IV) [stannic] coordination complex compound with some interesting properties.

Like many ammonium salts it’s very soluble in water. It’s a salt of a strong acid, H2SnCl6 (hexachlorostannic acid, which can be isolated as crystalline H2SnCl6.2H2O), and its solution in water is slightly acidic (from the ammonium ions). In hot, pure water hydrolysis of the anion tends to occur, with stannic hydroxide (Sn(OH)4) causing cloudiness of the solution. It’s therefore better dissolved in slightly acidified water (0.1 M HCl e.g.)

Ammonium hexachlorostannate is very soluble in 1 M HCl, both hot and cold. At BP the solubility in 1 M HCl is about 38 g/100 g. But in concentrated HCl (>20 %), both hot and cold, it’s solubility is very low, offering an easy route to recrystallisation.

The salt demonstrates the amphoterism of stannic compounds: add ammonia (or weak NaOH) to its solution and Sn(OH)4 precipitates. This precipitate redissolves both in strong acid (forming stannic salts) and in strong alkali (forming stannates - e.g. Na2Sn(OH)6).

Ammonium hexachlorostannate solutions are mild oxidisers: aluminium, zinc or magnesium metal will all be oxidised quickly with the tin being reduced to stannous (Sn (II)), which can be titrated with KMnO4 (e.g. for assaying purposes).

The pure compound, when heated strong in a hot Bunsen flame, sublimes leaving no ash: presumably the compound splits into NH4Cl and SnCl4 which are both volatile.

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CAS: 16960-53-5

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