lead monoxideSee lead(ii) oxide.
lead(II) oxide (lead monoxide)A
solid yellow compound, PbO, which
is insoluble in water; m.p. 886°C. It
exists in two crystalline forms:
litharge(tetrahedral; r.d. 9.53) and
massicot(rhombic; r.d. 8.0). It can be
prepared by heating the nitrate, and
is manufactured by heating molten
lead in air. If the temperature used is
lower than the melting point of the
oxide, the product is massicot; above
this, litharge is formed. Variations in
the temperature and in the rate of
cooling give rise to crystal vacancies
and red, orange, and brown forms of
litharge can be produced. The oxide
is amphoteric, dissolving in acids to
give lead(II) salts and in alkalis to
give *plumbates.
lead(IV) oxide (lead dioxide)A
dark brown or black solid with a ru-
tile lattice, PbO 2 , which is insoluble
in water and slightly soluble in con-
centrated sulphuric and nitric acids;
r.d. 9.375; decomposes at 290°C.
Lead(IV) oxide may be prepared by
the oxidation of lead(II) oxide by
heating with alkaline chlorates or ni-
trates, or by anodic oxidation of
lead(II) solutions. It is an oxidizing
agent and readily reverts to the
lead(II) oxidation state, as illustrated
by its conversion to Pb 3 O 4 and PbO
on heating. It reacts with hydrochlo-
ric acid to evolve chlorine. Lead(IV)
oxide has been used in the manufac-
ture of safety matches and was
widely used until the mid-1970s as an
adsorbent for sulphur dioxide in pol-
lution monitoring.lead(II) sulphateA white crys-
talline solid, PbSO 4 , which is virtually
insoluble in water and soluble in so-
lutions of ammonium salts; r.d. 6.2;
m.p. 1170°C. It occurs as the mineral
anglesite; it may be prepared in the
laboratory by adding any solution
containing sulphate ions to solutionsof lead(II) ethanoate. The material
known as basic lead(II) sulphate may
be made by shaking together lead(II)
sulphate and lead(II) hydroxide in
water. This material has been used in
white paint in preference to lead(II)
carbonate hydroxide, as it is not so
susceptible to discoloration through
reaction with hydrogen sulphide.
The toxicity of lead compounds has
led to a decline in the use of these
compounds.lead(II) sulphideA black crys-
talline solid, PbS, which is insoluble
in water; r.d. 7.5; m.p. 1114°C. It oc-
curs naturally as the metallic-looking
mineral *galena (the principal ore of
lead). It may be prepared in the labo-
ratory by the reaction of hydrogen
sulphide with soluble lead(II) salts.
Lead(II) sulphide has been used as an
electrical rectiÜer.lead tetra-acetateSee lead(iv)
ethanoate.lead(IV) tetraethyl (tetraethyl
lead)A colourless liquid, Pb(C 2 H 5 ) 4 ,
insoluble in water, soluble in ben-
zene, ethanol, ether, and petroleum;
r.d. 1.659; m.p. –137°C; b.p. 200°C. It
may be prepared by the reaction of
hydrogen and ethene with lead but a
more convenient laboratory and in-
dustrial method is the reaction of a
sodium–lead alloy with chloroethane.
A more recent industrial process is
the electrolysis of ethylmagnesium
chloride (the Grignard reagent) using
a lead anode and slowly running ad-
ditional chloroethane onto the cath-
ode. Lead tetraethyl is used in fuel
for internal-combustion engines
(along with 1,2-dibromoethane) to in-
crease the *octane number and re-
duce knocking. The use of lead(IV)
tetraethyl in petrol results in the
emission of hazardous lead com-
pounds into the atmosphere. Pres-
sure from environmental groups has
encouraged a reduction in the use oflead monoxide 322l