Potassium hexachlorostannate

Potassium hexachlorostannate is an inorganic chemical compound with the chemical formula K₂SnCl₆, used mainly for obtaining tin(IV) chloride.

Preparation

Potassium hexachlorostannate (IV) is prepared by dissolving tin metal (or pewter) in a mixture of nitric acid and hydrochloric acid (aqua regia). More or less stoichiometric amounts of the acids can be used in accordance with:

3 Sn(s) + 4 NO₃^-(aq) + 16 H⁺(aq) → 3 Sn⁴⁺(aq) + 4 NO(g) + 8 H₂O(l)

3 Sn⁴⁺(aq) + 18 HCl(aq) → 3 SnCl₆^2-(aq) + 18 H⁺(aq)

Dissolution is very swift and does not usually require heating.

Once complete the solution is brought to a gentle simmer and solid KCl is added, 2 mol per mol of tin. The mixture is then simmered and stirred until all the KCl is dissolved, then allowed to cool naturally, then further chilled on ice bath, e.g. overnight.

Well-formed crystals of K₂SnCl₆ are obtained.

Ammonium hexachlorostannate is obtained in identical conditions but by replacing KCl with NH₄Cl.

Instead of pure tin, pewter (Sn/Sb alloy) can also be used because the corresponding Sb salt, KSbCl₆ is very soluble even at low temperature and simply stays in solution.

The salts can also be obtained by oxidation of an SnCl₂ solution in HCl, with hydrogen peroxide or nitric acid as oxidiser. Add KCl (or NH₄Cl) as per above.

Potassium hexachlorostannate is the salt of a strong acid and its solutions react neutral in water. Addition of alkali or ammonia solution precipitates Sn(OH)₄·nH₂O. Further addition of strong alkali causes soluble stannate (K₂Sn(OH)₆) to form.

It is insoluble in 37 w% HCl which offers an easy method of purifying the salt.

On strong heating (> 300 C, est.) it releases SnCl₄ (B.P. 114.15 °C), so it affords a chlorine-free route to this useful chemical. The ammonium salt sublimes completely.

Projects

• Make tin(IV) chloride