Stannous Hydroxide

The white precipitate obtained by adding alkali hydroxide or carbonate solution to stannous chloride is said not to be Sn(OH)₂, but to have the composition 2SnO.H₂O. If this precipitate is heated above 80° C. it loses water, and passes into the anhydrous oxide. The hydroxide dissolves in excess of alkali producing a solution of alkali stannite, which, according to Hantzsch, is not Sn(ONa)₂, but H.SnO.ONa, there being no ground for assuming the existence of SnO₂'' ions. Thus tin becomes quadrivalent in stannites, and the hydroxide is a feeble acid of the type of formic acid.

This conclusion in regard to constitution, which applies to the hydroxides of zinc, glucinum, lead, tin, and germanium, is based upon measurements of the conductivities of their alkaline solutions, and the rate at which these solutions hydrolyse ethyl acetate. The metals are named in the order of increasing acidic strength of their hydroxides. It is interesting to remember that carbon monoxide combines similarly with alkali:

CO + NaOH → HCOONa,

and that there are other acids probably constituted in an analogous manner, so that the maximum valency of the nuclear atoms is reached, e.g. HSO₂OH, H₂POOH, and HPO(OH)₂. It may be remarked, however, that this constitution of stannites involves the union of a hydrogen and a tin atom, otherwise unknown. The reducing action of sodium stannite solution has been studied by Goldschmidt and Eckardt, who agree with Hantzsch in regard to the constitution of this salt.