convert the PbO on the negative
plate into a sponge ofÜnely divided
lead. On the positive plate the PbO is
converted to lead(IV) oxide (PbO 2 ).
The equation for the overall reaction
during discharge is:
PbO 2 + 2H 2 SO 4 + Pb →2PbSO 4 +
2H 2 OThe reaction is reversed during
charging. Each cell gives an e.m.f. of
about 2 volts and in motor vehicles a
12-volt battery of six cells is usually
used. The lead–acid battery produces
80–120 kJ per kilogram. Compare
nickel–iron accumulator.
lead(II) carbonate A white solid,
PbCO 3 , insoluble in water; rhombic;
r.d. 6.6. It occurs as the mineral
*cerussite, which is isomorphous
with aragonite and may be prepared
in the laboratory by the addition of
cold ammonium carbonate solution
to a cold solution of a lead(II) salt (ac-
etate or nitrate). It decomposes at
315 °C to lead(II) oxide and carbon
dioxide.
lead(II) carbonate hydroxide
(white lead; basic lead carbonate)A
powder, 2PbCO 3 .Pb(OH) 2 , insoluble in
water, slightly soluble in aqueous
carbonate solutions; r.d. 6.14; decom-
poses at 400°C. Lead(II) carbonate hy-
droxide occurs as the mineral
hydroxycerussite (of variable compo-
sition). It was previously manufac-
tured from lead in processes using
spent tanning bark or horse manure,
which released carbon dioxide. It is
currently made by electrolysis of
mixed solutions (e.g. ammonium ni-
trate, nitric acid, sulphuric acid, and
acetic acid) using lead anodes. For the
highest grade product the lead must
be exceptionally pure (known in the
trade as ‘corroding lead’) as small
amounts of metallic impurity impart
grey or pink discolorations. The ma-
terial was used widely in paints, both
for art work and for commerce, but
it has the disadvantage of reacting
with hydrogen sulphide in industrial
atmospheres and producing black
lead sulphide. The poisonous nature
of lead compounds has also con-
tributed to the declining importance
of this material.lead-chamber process An obso-
lete method of making sulphuric
acid by the catalytic oxidation of sul-
phur dioxide with air using a potas-
sium nitrate catalyst in water. The
process was carried out in lead con-
tainers (which was expensive) and
only produced dilute acid. It was re-
placed in 1876 by the *contact
process.lead dioxideSee lead(iv) oxide.lead(II) ethanoate (lead(II) ac-
etate) A white crystalline solid,
Pb(CH 3 COO) 2 , soluble in water and
slightly soluble in ethanol. It exists as
the anhydrous compound (r.d. 3.25;
m.p. 280°C), as a trihydrate,
Pb(CH 3 COO) 2 .3H 2 O (monoclinic; r.d.
2.55; loses water at 75°C), and as a
decahydrate, Pb(CH 3 COO) 2 .10H 2 O
(rhombic; r.d. 1.69). The common
form is the trihydrate. Its chief inter-
est stems from the fact that it is solu-
ble in water and it also forms a
variety of complexes in solution. It
was once known as sugar of lead be-
cause of its sweet taste.lead(IV) ethanoate (lead tetra-
acetate)A colourless solid,
Pb(CH 3 COO) 4 , which decomposes in
water and is soluble in pure ethanoic
acid; monoclinic; r.d. 2.228; m.p.
175 °C. It may be prepared by dissolv-
ing dilead(II) lead(IV) oxide in warm
ethanoic acid. In solution it behaves
essentially as a covalent compound
(no measurable conductivity) in con-
trast to the lead(II) salt, which is a
weak electrolyte.lead(IV) hydrideSee plumbane.321 lead(IV) hydride
l