Tin II Oxide SnO

The preparation involves conversion of tin (II) chloride to hydrated tin (II) oxide, which is then dehydrated to SnO by extended heatii in an aqueous solution. 

Pure SnO should yield a clear solution with hydrochloric acid, but a very slight opalescence is acceptable. 

Formula weight 134.70. Blue-black, crystalline substance with metallic sheen. In air, is oxidized to SnOg above 220°C in inert gas, decomposes to Sn and SngO at 400°C. An SnO melt is stable and hardens (with simultaneous disproportionation into Sn and SngO ) at 1040°C. Above 1000°C, SnO attacks silicate-containing materials, forming Sn (II) silicate vessels made of sintered corimdum may beusedigito 1600°C. B.p. (estimated) 1700°C, d 6.32. 

Insoluble in water soluble in acids, yielding Sn (II) salts. 

An agitated solution of NagSn(OH)g (see section on hydroxy salts) is slowly allowed to reacrt with dilute hydrochloric acid at room temperature until the mixture is almost neutral. The copious (X-stannic acid precipitate settling out is treated as in method I. Complete removal of adsorbed foreign ions, particularly Na, presents greater difficulty here than in method I, where no alkali is used. 

---

Many metallic elements in the p and d blocks, have atoms that can lose a variable number of electrons. As we saw in Section 1.19, the inert-pair effect implies that the elements listed in Fig. 1.57 can lose either their valence p-electrons alone or all their valence p- and s-electrons. These elements and the d-block metals can form different compounds, such as tin(II) oxide, SnO, and tin(IV) oxide, Sn02, for tin. The ability of an element to form ions with different charges is called variable valence. 

Tin(II) oxide is a dark-coloured powder which oxidises spontaneously in air with the evolution of heat to give tin(IV) oxide, SnO, ... 

Stannous Oxide. Stannous oxide, SnO ((tin(II) oxide), mol wt 134.70, sp gr 6.5) is a stable, blue-black, crystalline product that decomposes at above 385°C. It is insoluble in water or methanol, but is readily soluble in acids and concentrated alkaHes. It is generally prepared from the precipitation of a stannous oxide hydrate from a solution of stannous chloride with alkaH. Treatment at controUed pH in water near the boiling point converts the hydrate to the oxide. Stannous oxide reacts readily with organic acids and mineral acids, which accounts and for its primary use as an intermediate in the manufacture of other tin compounds. Minor uses of stannous oxide are in the preparation of gold—tin and copper—tin mby glass. 

SnO and hydrous tin(II) oxide are amphoteric, dissolving readily in aqueous acids to give Sn" or its complexes, and in alkalis to give the pyramidal Sn(OH)3 at intermediate values of pH, condensed basic oxide-hydroxide species form, e.g. [(OH)2SnOSn(OH)2] and [Sn3(OH)4] +, etc. Analytically, the hydrous oxide frequently has a composition close to 3Sn0.H20 and an X-ray study shows it to... 

Tin forms two series of compounds tin(II) or stannous compounds and tint IV1 or stannic compounds. Tin(ll) oxide, SnO, insoluble in water, is formed by precipitation of an SnO hydrate from an S11CL solution with alkali and later treatment in water (near the boiling point and at constant pH). It is amphiprotic, but only slightly acid, forming stannites slowly with strong alkalis. Sodium stannite is conveniently prepared from... 

The common form of SnO is the black tetragonal orthorhombic modification (density 6-32). It is prepared by the hydrolysis of tin(II) salts to hydrated tin(II) oxide, with subsequent dehydration. Special care has to be taken with reagents and with conditions to obtain pure samples. This black oxide has a layer structure in which the tin atom lies at the apex of a square pyramid, the base of which is formed by the four nearest oxygen atoms (Sn-O = 2-21 A). The Sn-Sn distance between the layers at 3-70 A is so close to that of the Sn-Sn distance in tin metal, that some mode of tin-tin interaction cannot be ruled OUt58. 

The precipitate obtained is in fact colloidal and has no definite composition. Careful drying of the precipitate gives the anhydrous oxide, SnO, which may also be prepared by heating tin(II) ethane-dioate (oxalate) ... 

Tin(ll) oxide gives the trihydroxostan-nate(ll) ion in alkaline solutions SnO(s) + OH-(aq) + HjOd) Sn(OH)3-(aq) Staimate(rV) compounds were formerly referred to as orthostannates (Sn04 ) or metastannates (SnOa ). Stannate(II) compounds were called stannites. 

Tin(II) sulfide is oxidized by HNO3 to meta-tin(lV) hydrous oxide. Other Sn salts and SnO, as well as freshly precipitated (ortho) SnO(OH)2-aq, when heated with HNO3 likewise yield the much less soluble Sn02 aq. Nitrous acid gives similar results. 

Romarchite is a tm(II) oxide mineral with composition SnO. It is a secondary mineral which occurs as thin soft black crusts with metallic lustre, or as microscopic laths, formed as a weathering product of tin compounds. It was first reported by Organ and Mandarine (1971) as a corrosion product of tin pannikins which had been immersed in water at Boundary Falls (Ontario, Canada). Romarchite is named after the acronym for the Royal Ontario Museum of archaeology, and is often found in association with the hydroxyl-bearing form hydroromarchite, which also has tetragonal symmetry. 

A red orthorhombic modification of SnO is formed by heating suspensions of the white hydrous oxide. The red metastable form can be stabilized by the presence of about 1% phosphite, but if ammonia is used in the hydrolysis of the tin(II) chloride solutions, a red form of SnO is formed in the absence of stabilizing phosphite. ... 

---