Lead
Lead is a bluish white lustrous metal. It is very soft and
has a relatively low melting point. It can be made into wires, sheets and foils
very easily and as such is used for construction purposes. Lead quickly
tarnishes in air. This gives the metal its characteristic grey look. Once it is
tarnished, it is covered by a protective layer, which makes further corrosion of
the metal almost impossible. The corrosion-resistance of the metal also is an
important reason for its widespread use in construction and building.
The metal is not attacked appreciably by sulphuric acid, due to formation of an insoluble layer of lead sulfate. Lead bottles in fact are very suitable for handling sulphuric acid. Lead is attacked very slowly by hydrochloric acid. This is due to the low solubility of lead chloride. However, in the long run, lead very slowly is corroded by hydrochloric acid. In nitric acid, lead dissolves quite well. Lead nitrate is soluble in water very well and hence, no protective layer is formed in nitric acid.
Lead can be obtained at high purity in powder form from eBay. It also is available at fairly high purity as shot for guns and as sheets for construction purposes. All these forms of lead can be used as a starting point for experimenting with lead compounds. However, direct purchase of lead nitrate or lead acetate is preferable, when one wants to experiment with lead compounds.
Lead metal, as it
is used in construction purposes is not very toxic, because of its very low rate
of corrosion. Compounds of lead, however, are very toxic, both for humans and
for the environment.
In its compounds, lead exists in the +2 and the +4 oxidation states. The lead (II) ion is a colorless ion in aqueous solution, which hydrolyses to a large extent. Lead (IV) cannot exist in aqueous solution as a simple ion. In its +4 oxidation state, lead usually exists as its oxide, brown PbO2 or in a mixed oxidation state compound, red/orange Pb3O4. For the general public, the following compounds are available:
- lead acetate, Pb(CH3COO)2·3H2O
- lead nitrate, Pb(NO3)2
- lead (IV) oxide, PbO2
- lead (II, IV) oxide, Pb3O4
- lead chromate, PbCrO4
Most uses of lead compounds are banned, due to the toxicity of lead. For this reason, it is becoming harder to obtain lead compounds. It might be possible that at certain art and paint shops, the bright orange/red Pb3O4 is available. Lead chromate is available at pottery and ceramics supply shops. The other lead compounds only are available from chemical supply houses.
Lead
acetate is a white crystalline solid, which easily dissolves in water. Lead
acetate has a fairly strong covalent character. Its solutions only are partially
ionized. Lead acetate, if available, is an interesting lead compound. The
acetate ion does not interfere with most experiments.
Lead
nitrate also is a white crystalline solid. Like lead acetate, this solid easily
can be dissolved in water. It is a good alternative for lead acetate. There is
no need to have both lead nitrate and lead acetate at hand. Lead nitrate can
fairly easily be prepared by the home chemist, by dissolving lead metal in
concentrated nitric acid and filtering and rinsing the white crystalline solid,
which is formed.
This
must be done outside, due to formation of nitrous vapors and formation of very
small droplets, which may contain lead nitrate!
Lead
(IV) oxide is a chocolate brown solid, insoluble in water. It is a strong
oxidizer. It can be prepared from any soluble lead (II) salt by precipitating
the lead with a soluble hydroxide and treating this with a solution of a
persulfate. Lead (IV) oxide otherwise can only be obtained from chemical supply
houses. Lead (IV) oxide conducts electricity. In its compressed form it is used
for electrodes, which are very resistant against anodic corrosion. This makes
lead (IV) oxide electrodes very good as anode for electrolysis experiments.
Lead
(II, IV) oxide is used sometimes as an orange/red pigment. It is not soluble in
water. It can act as an oxidizer. For the home chemist this is not a really
interesting compound.
Lead
chromate is an insoluble bright yellow compound, which is also sold as chromate
yellow. It is soluble somewhat in dilute nitric acid, in which the chromate goes
into solution as dichromate, chromic acid and free lead (II) ions. For the home chemist,
lead chromate is not a really interesting compound, because of the fact that the
properties of the chromate (or dichromate in acidic media) strongly interfere
with the properties of lead.
