used as a bleaching agent. With
acids, hydrogen peroxide is formed
and the reaction is used in the laboratory preparation of hydrogen peroxide.
barium sulphate An insoluble
white solid, BaSO 4 , that occurs naturally as the mineral *barytes (or
heavy spar) and can be prepared as a
precipitate by adding sulphuric acid
to barium chloride solution; r.d. 4.50;
m.p. 1580°C. The rhombic form
changes to a monoclinic form at
1149°C. It is used as a raw material
for making other barium salts, as a
pigment extender in surface coating
materials (called blanc Üxe), and
in the glass and rubber industries.
Barium compounds are opaque to
X-rays, and a suspension of the sulphate in water is used in medicine to
provide a contrast medium for X-rays
of the stomach and intestine. Although barium compounds are extremely poisonous, the sulphate is
safe to use because it is very insoluble.
barrel A measurement of volume,
widely used in the chemical industry,
equal to 35 UK gallons (approximately 159 litres).
Bartlett, Neil (1932– ) British inorganic chemist who prepared oxygen hexachloroplatinate in 1961 and,
in 1962, xenon hexachloroplatine –
the Ürst compound of a noble gas.
Barton, Sir Derek (Harold
Richard) (1918–98) British organic
chemist who worked on steroids and
other natural products. He is noted
for his investigations into the conformation of organic compounds and its
effect on chemical properties. Barton
was awarded the 1969 Nobel Prize
for chemistry (with O. Hassell
(1897–1981)).
baryta See barium hydroxide.
barytes (barite) An orthorhombic
mineral form of *barium sulphate,
BaSO 4 ; the chief ore of barium. It is
usually white but may also be yellow,
grey, or brown. Large deposits occur
in Andalusia, Spain, and in the USA.
basal See apical.
basalt A Üne-grained basic igneous
rock. It is composed chieÛy of calcium-rich plagioclase feldspar and
pyroxene; other minerals present
may be olivine, magnetite, and apatite. Basalt is the commonest type of
lava.
base A compound that reacts with a
protonic acid to give water (and a
salt). The deÜnition comes from the
Arrhenius theory of acids and bases.
Typically, bases are metal oxides, hydroxides, or compounds (such as ammonia) that give hydroxide ions in
aqueous solution. Thus, a base may
be either: (1) An insoluble oxide or
hydroxide that reacts with an acid,
e.g.
CuO(s) + 2HCl(aq) → CuCl 2 (aq) +
H 2 O(l)
Here the reaction involves hydrogen
ions from the acid
CuO(s) + 2H
+ (aq) → H 2 O(l) +
Cu
2+
(aq)
(2) A soluble hydroxide, in which
case the solution contains hydroxide
ions. The reaction with acids is a reaction between hydrogen ions and
hydroxide ions:
H
+ + OH
–
→ H 2 O
(3) A compound that dissolves in
water to produce hydroxide ions.
For example, ammonia reacts as follows:
NH 3 (g) + H 2 O(l) ˆ NH 4
+ (aq) +
–
OH
Similar reactions occur with organic
*amines (see also nitrogenous base;
amine salts). A base that dissolves in
water to give hydroxide ions is called
barium sulphate
58
b
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acids, hydrogen peroxide is formed
and the reaction is used in the laboratory preparation of hydrogen peroxide.
barium sulphate An insoluble
white solid, BaSO 4 , that occurs naturally as the mineral *barytes (or
heavy spar) and can be prepared as a
precipitate by adding sulphuric acid
to barium chloride solution; r.d. 4.50;
m.p. 1580°C. The rhombic form
changes to a monoclinic form at
1149°C. It is used as a raw material
for making other barium salts, as a
pigment extender in surface coating
materials (called blanc Üxe), and
in the glass and rubber industries.
Barium compounds are opaque to
X-rays, and a suspension of the sulphate in water is used in medicine to
provide a contrast medium for X-rays
of the stomach and intestine. Although barium compounds are extremely poisonous, the sulphate is
safe to use because it is very insoluble.
barrel A measurement of volume,
widely used in the chemical industry,
equal to 35 UK gallons (approximately 159 litres).
Bartlett, Neil (1932– ) British inorganic chemist who prepared oxygen hexachloroplatinate in 1961 and,
in 1962, xenon hexachloroplatine –
the Ürst compound of a noble gas.
Barton, Sir Derek (Harold
Richard) (1918–98) British organic
chemist who worked on steroids and
other natural products. He is noted
for his investigations into the conformation of organic compounds and its
effect on chemical properties. Barton
was awarded the 1969 Nobel Prize
for chemistry (with O. Hassell
(1897–1981)).
baryta See barium hydroxide.
barytes (barite) An orthorhombic
mineral form of *barium sulphate,
BaSO 4 ; the chief ore of barium. It is
usually white but may also be yellow,
grey, or brown. Large deposits occur
in Andalusia, Spain, and in the USA.
basal See apical.
basalt A Üne-grained basic igneous
rock. It is composed chieÛy of calcium-rich plagioclase feldspar and
pyroxene; other minerals present
may be olivine, magnetite, and apatite. Basalt is the commonest type of
lava.
base A compound that reacts with a
protonic acid to give water (and a
salt). The deÜnition comes from the
Arrhenius theory of acids and bases.
Typically, bases are metal oxides, hydroxides, or compounds (such as ammonia) that give hydroxide ions in
aqueous solution. Thus, a base may
be either: (1) An insoluble oxide or
hydroxide that reacts with an acid,
e.g.
CuO(s) + 2HCl(aq) → CuCl 2 (aq) +
H 2 O(l)
Here the reaction involves hydrogen
ions from the acid
CuO(s) + 2H
+ (aq) → H 2 O(l) +
Cu
2+
(aq)
(2) A soluble hydroxide, in which
case the solution contains hydroxide
ions. The reaction with acids is a reaction between hydrogen ions and
hydroxide ions:
H
+ + OH
–
→ H 2 O
(3) A compound that dissolves in
water to produce hydroxide ions.
For example, ammonia reacts as follows:
NH 3 (g) + H 2 O(l) ˆ NH 4
+ (aq) +
–
OH
Similar reactions occur with organic
*amines (see also nitrogenous base;
amine salts). A base that dissolves in
water to give hydroxide ions is called
barium sulphate
58
b
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