Modern inorganic chemistry

GROUP IV 169
swells because oxygen atoms become attached to some of the carbon
atoms in the rings and distend the layer structure. 'Graphite oxide'
is rather indefinite in composition. With concentrated sulphuric acid
and an oxidising agent a blue solution called 'graphite hydrogen
sulphate' is formed; this has an approximate formula (CJ^HSOJ.
2H 2 SO 4 *.
Amorphous carbon, having a far greater effective surface area
than either diamond or graphite, is the most reactive form of carbon.
It reacts with both hot concentrated sulphuric and hot concentrated
nitric acids in the absence of additional oxidising agents but is not
attacked by hydrochloric acid.

Silicon

Silicon, like carbon, is unaffected by dilute acids. Powdered silicon

dissolves incompletely in concentrated nitric acid to give insoluble

silicon dioxide, SiO 2 :

3Si 4- 4HNO 3 -> 3SiO 2 + 4NO + 2H 2 O

Germanium

The gradual increase in electropositive character down the group

is clearly shown in that, unlike both carbon and silicon, germanium

very readily dissolves in both concentrated nitric and sulphuric

acids; the hydrated germanium(IV) oxide is produced:

3Ge + 4HNO 3 -> 3GeO 2 + 4NO + 2H 2 O

Germanium, however, does not react with either dilute sulphuric or

dilute hydrochloric acid, unlike tin, the next element in the group.

Tin

Tin slowly dissolves in dilute hydrochloric, nitric and sulphuric
acids, and is in fact the only Group IV element to do so. The reac-
tions with more concentrated acid are rapid. With hydrochloric acid,

• Graphite reacts with alkali metals, for example potassium, to form compounds
  which are non-stoichiometric but which all have limiting compositions (for example
  KnC); in these, the alkali metal atoms are intercalated between the layers of carbon
  atoms. In the preparation of fluorine by electrolysis of a molten fluoride with graphite
  electrodes the solid compound (CF)B, polycarbon fluoride is formed, with fluorine on
  each carbon atom, causing puckering of the rings.