A compound formed by reaction of tin oxides (or hydroxides) with alkali. Tin oxides are amphoteric (weakly acidic) and react to give stannate ions. Tin(IV) oxide with molten alkali gives the stannate(IV) ion SnO2+2OH− → SnO32−+H2O In fact, there are various ions present in which the tin is bound to hydroxide groups, the main one being the hexahydroxostannate(IV) ion, Sn(OH)62−. This is the negative ion present in crystalline ‘trihydrates’ of the type K2Sn2O3.3H2O. Tin(II) oxide gives the trihydroxostannate(II) ion in alkaline solutions SnO(s)+OH−(aq)+H2O(l) → Sn(OH)3−(aq) Stannate(IV) compounds were formerly referred to as orthostannates (SnO44−) or metastannates (SnO32−). Stannate(II) compounds were called stannites.
SnO2+2OH− → SnO32−+H2O
SnO(s)+OH−(aq)+H2O(l) → Sn(OH)3−(aq)