Modern inorganic chemistry

200 GROUP IV

LEAD(II) IODIDE

The solid has a layer structure (p. 434). Lead(II) iodide, like lead(II)

chloride, is soluble in hot water but on cooling, appears in the form

of glistening golden 'spangles'. This reaction is used as a test for

lead(II) ions in solution.

LEAD(IV) CHLORIDE

Unlike solid lead(II) chloride which is ionic and which dissolves in

water to form hydrated Pb2+ and Cl~ ions, lead(IV) chloride is an

essentially covalent volatile compound which is violently hydrolysed

by water.

Lead(IV) chloride is formed from cold concentrated hydrochloric

acid and lead(IV) oxide as described earlier. It readily evolves

chlorine by the reversible reaction:

PbCl 4 ^ PbCl 2 + C1 2 |
Hence, if chlorine is passed into a cold suspension (in hydrochloric
acid) of lead(II) chloride, lead(IV) chloride is formed. Addition of
ammonium chloride gives the complex salt ammonium hexachloro-
plumbate(IV) as a yellow precipitate:

2NH 4 C1 + PbCl 4 -> (NH 4 ) 2 PbIVCl 6 i

This is filtered off and cold concentrated sulphuric acid added, when
lead(IV) chloride separates as an oily yellow liquid:

(NH 4 ) 2 PbCl 6 + H 2 SO 4 -+(NH 4 ) 2 SO 4 + PbCl 4 + 2HC1

OTHER IMPORTANT COMPOUNDS

Carbon

CARBIDES

These can be divided into three groups:
The salt-like carbides: Among these are aluminium tricarbide
(methanide) A1 4 C 3 (containing essentially C^4 ~ ions) in the crystal
lattice and the rather more common dicarbides containing the C\ ~
ion, for example calcium dicarbide CaC 2 ; these carbides are
hydrolysed by water yielding methane and ethyne respectively:

A1 4 C 3 + 12H 2 O -> 4A1(OH) 3 + 3CHJ

CaC 2 + 2H 2 O -> Ca(OH) 2 + C 2 H 2 |