Modern inorganic chemistry

194 GROUP IV

LEAD(IV) OXIDE, PbO 2

Lead(IV) oxide can be prepared by the action of an alkaline

chlorate(I) solution on a solution of a lead(II) salt. The reaction can

be considered in two stages:

(1) Pb2+ + 2OH" -> Pb(OH) 2 l

white

The white precipitate of lead hydroxide (or hydrated lead(II) oxide)
is then oxidised by the chlorate(I) to the brown dioxide:

(2) Pb(OH) 2 + C1O~ -> PbO 2 i + CT + H 2 O

brown

Lead(IV) oxide is also obtained when 'red lead', Pb 3 O 4 (see below),
is treated with dilute nitric acid:

Pb 3 O 4 + 4HNO 3 -» 2Pb(NO 3 ) 2 + 2H 2 O + PbO 2 |

When heated above 600 K lead(IV) oxide decomposes into the more
stable lead(II) oxide and oxygen :

2PbO 2 -> 2PbO 4- O 2 t

Lead(IV) oxide is found to have a considerable oxidising power,
again indicating that the oxidation state +2 is generally more
stable for lead than oxidation state +4. Concentrated hydrochloric
acid, for example, reacts with PbO 2 at room temperature to form
lead(II) chloride and chlorine:

PbO 2 + 4HC1 -+ PbCU + C1 2 | 4- 2H 2 O

If this reaction is carried out at 273 K some unstable lead(IV)
chloride is initially formed (p. 200). Other oxidising reactions of
lead(IV) oxide include the evolution of oxygen when heated with
concentrated sulphuric acid:

2PbO 2 4- 2H 2 SO 4 -» 2PbSO 4 + 2H 2 O 4- O 2 t

and the oxidation of sulphur to sulphur dioxide which then reacts
with more lead(IV) oxide to form lead(II) sulphate:

PbO 2 + S -* Pb + SO 2

PbO 2 + SO 2 -> PbSO 4

Lead dioxide is slightly soluble in concentrated nitric acid and
concentrated sulphuric acid, and it dissolves in fused alkalis. It
therefore has amphoteric properties, although these are not well
characterised since it is relatively inert.