Modern inorganic chemistry

192 GROUP IV

The anhydrous oxide is obtained by ignition of the hydrated oxide

produced.

Germanium(IV) oxide is less acidic than silicon(IV) oxide but

reacts readily with alkali forming germanates(IV), the greater

reactivity of the germanium(IV) oxide being attributable to the

slight solubility of the quartz form of GeO 2 in water. Germanium

forms a few salts containing the ion [Ge(OH) 6 ]^2 ~ e.g. Fe[Ge(OH) 6 ].

Oxides of tin

TIN(II) OXIDE

If a solution of a tin(II) salt is treated with a small amount of an

alkali, tin(II) hydroxide is precipitated, the reaction being repre-

sented by the equation:

Sn2+ + 2OH" ->Sn(OH) 2 i

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):

SnC 2 O 4 -* SnO 4- COf + CO 2 f

Tin(II) oxide is a dark-coloured powder which oxidises spon-

taneously in air with the evolution of heat to give tin(IV) oxide, SnO 2 :

2SnO + O 2 -> SnO 2

It is amphoteric; it gives tin(II) salts with dilute acids and hydroxo-

stannates(II) with alkalis, for example:

SnO + 2HC1-* SnCl 2 4- H 2 O

SnO 4- H 2 O + OH" ^ [Sn(OH) 3 ]~

Stannate(II) ions are powerful reducing agents. Since, for tin, the

stability of oxidation state +4 is greater than that of oxidation

state +2, tin(II) always has reducing properties, but these are

greater in alkaline conditions than in acid (an example of the effect

of pH on the redox potential, p. 101).

TIN(IV) OXIDE, SnO 2

Tin(IV) oxide occurs naturally, clearly indicating its high stability.
It can be prepared either by heating tin in oxygen or by heating the