white amorphous deliquescent solid,
As 2 O 5 ; r.d. 4.32; decomposes at
315 °C. It is soluble in water and
ethanol. Arsenic(V) oxide cannot be
obtained by direct combination of ar-
senic and oxygen; it is usually pre-
pared by the reaction of arsenic with
nitric acid followed by dehydration
of the arsenic acid thus formed. It
readily loses oxygen on heating to
give arsenic(III) oxide. Arsenic(V)
oxide is acidic, dissolving in water to
give arsenic(V) acid (formerly called
arsenic acid), H 3 AsO 4 ; the acid is trib-
asic and slightly weaker than phos-
phoric acid and should be visualized
as (HO) 3 AsO. It gives arsenate(V)salts
(formerly called arsenates).
arsenic trioxideSee arsenic(iii)
oxide.
arsenious acidSee arsenic(iii)
oxide.
arsenious oxideSee arsenic(iii)
oxide.
arseniteSee arsenic(iii) oxide.
arsenolite A mineral form of *ar-
senic(III) oxide, As 4 O 6.
arsine(arsenic hydride)A colourless
gas, AsH 3 ; m.p. –116.3°C; b.p. –55°C.
It is soluble in water, chloroform,
and benzene. Liquid arsine has a rela-
tive density of 1.69. Arsine is pro-
duced by the reaction of mineral
acids with arsenides of electroposi-
tive metals or by the reduction of
many arsenic compounds using
nascent hydrogen. It is extremely
poisonous and, like the hydrides of
the heavier members of group 15
(formerly VB), is readily decomposed
at elevated temperatures (around
260–300°C). Like ammonia and phos-
phine, arsine has a pyramidal struc-
ture.
Arsine gas has a very important
commercial application in the pro-
duction of modern microelectronic
components. It is used in a dilute gas
mixture with an inert gas and its
ready thermal decomposition is ex-
ploited to enable other growing crys-
tals to be doped with minute traces
of arsenic to give n-type semiconduc-
tors.artiniteA mineral form of basic
*magnesium carbonate,
MgCO 3 .Mg(OH) 2 .3H 2 O.aryl group A group obtained by re-
moving a hydrogen atom from an
aromatic compound, e.g. phenyl
group, C 6 H 5 –, derived from benzene.aryneA compound that can be re-
garded as formed from an arene by
removing two adjacent hydrogen
atoms to convert a double bond into
a triple bond. Arynes are transient in-
termediates in a number of reactions.
The simplest example is *benzyne.asbestosAny one of a group of
Übrous amphibole minerals (amosite,
crocidolite (blue asbestos), tremolite,
anthophyllite, and actinolite) or the
Übrous serpentine mineral chrysotile.
Asbestos has widespread commercial
uses because of its resistance to heat,
chemical inertness, and high electri-
cal resistance. TheÜbres may be
spun and woven intoÜreproof cloth
for use in protective clothing, cur-
tains, brake linings, etc., or moulded
into blocks. Since the 1970s short as-
bestosÜbres have been recognized as
a cause of asbestosis, a serious lung
disorder, and mesothelioma, a fatal
form of lung cancer. These concerns
have limited its use and imposed
many safety procedures when it is
used. Canada is the largest producer
of asbestos; others include Russia,
South Africa, Zimbabwe, and China.ascorbic acidSee vitamin c.asparagineSee amino acid.aspartic acidSee amino acid.45 aspartic acid
a