per(II) acetate, is added to the test solution and boiled. If any reducing
sugars are present a red precipitate
of copper(II) oxide is formed. The reaction will be negative in the presence of disaccharide sugars as they
are weaker reducing agents.
barite See barytes.
barium Symbol Ba. A silvery-white
reactive element belonging to *group
2 (formerly IIA) of the periodic table;
a.n. 56; r.a.m. 137.34; r.d. 3.51; m.p.
725°C; b.p. 1640°C. It occurs as the
minerals barytes (BaSO 4 ) and
witherite (BaCO 3 ). Extraction is by
high-temperature reduction of barium oxide with aluminium or silicon
in a vacuum, or by electrolysis of
fused barium chloride. The metal is
used as a getter in vacuum systems.
It oxidizes readily in air and reacts
with ethanol and water. Soluble barium compounds are extremely poisonous. It was Ürst identiÜed in 1774 by
Karl *Scheele, and was extracted by
Humphry *Davy in 1808.
A
• Information from the WebElements site
barium bicarbonate See barium
hydrogencarbonate.
barium carbonate A white insoluble compound, BaCO 3 ; r.d. 4.43. It decomposes on heating to give barium
oxide and carbon dioxide:
BaCO 3 (s) → BaO(s) + CO 2 (g)
The compound occurs naturally as
the mineral witherite and can be prepared by adding an alkaline solution
of a carbonate to a solution of a barium salt. It is used as a raw material
for making other barium salts, as a
Ûux for ceramics, and as a raw material in the manufacture of certain
types of optical glass.
barium chloride A white compound, BaCl 2 . The anhydrous compound has two crystalline forms: an
α form (monoclinic; r.d. 3.856),
which transforms at 962°C to a β
form (cubic; r.d. 3.917; m.p. 963°C;
b.p. 1560°C). There is also a dihydrate, BaCl 2 .2H 2 O (cubic; r.d. 3.1),
which loses water at 113°C. It is prepared by dissolving barium carbonate
(witherite) in hydrochloric acid and
crystallizing out the dihydrate. The
compound is used in the extraction
of barium by electrolysis.
barium hydrogencarbonate (barium bicarbonate) A compound,
Ba(HCO 3 ) 2 , which is only stable in solution. It can be formed by the action
of carbon dioxide on a suspension of
barium carbonate in cold water:
BaCO 3 (s) + CO 2 (g) + H 2 O(l) →
Ba(HCO 3 ) 2 (aq)
On heating, this reaction is reversed.
barium hydroxide (baryta) A
white solid, Ba(OH) 2 , sparingly soluble in water. The common form is
the octahydrate, Ba(OH) 2 .8H 2 O; monoclinic; r.d. 2.18; m.p. 78°C. It can be
produced by adding water to barium
monoxide or by the action of sodium
hydroxide on soluble barium compounds and is used as a weak alkali
in volumetric analysis.
barium oxide A white or yellowish
solid, BaO, obtained by heating barium in oxygen or by the thermal decomposition of barium carbonate or
nitrate; cubic; r.d. 5.72; m.p. 1923°C;
b.p. 2000°C. When barium oxide is
heated in oxygen the peroxide, BaO 2 ,
is formed in a reversible reaction
that was once used as a method for
obtaining oxygen (the Brin process).
Barium oxide is now used in the
manufacture of lubricating-oil additives.
barium peroxide A dense offwhite solid, BaO 2 , prepared by carefully heating *barium oxide in
oxygen; r.d. 4.96; m.p. 450°C. It is
57
barium peroxide
b
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sugars are present a red precipitate
of copper(II) oxide is formed. The reaction will be negative in the presence of disaccharide sugars as they
are weaker reducing agents.
barite See barytes.
barium Symbol Ba. A silvery-white
reactive element belonging to *group
2 (formerly IIA) of the periodic table;
a.n. 56; r.a.m. 137.34; r.d. 3.51; m.p.
725°C; b.p. 1640°C. It occurs as the
minerals barytes (BaSO 4 ) and
witherite (BaCO 3 ). Extraction is by
high-temperature reduction of barium oxide with aluminium or silicon
in a vacuum, or by electrolysis of
fused barium chloride. The metal is
used as a getter in vacuum systems.
It oxidizes readily in air and reacts
with ethanol and water. Soluble barium compounds are extremely poisonous. It was Ürst identiÜed in 1774 by
Karl *Scheele, and was extracted by
Humphry *Davy in 1808.
A
• Information from the WebElements site
barium bicarbonate See barium
hydrogencarbonate.
barium carbonate A white insoluble compound, BaCO 3 ; r.d. 4.43. It decomposes on heating to give barium
oxide and carbon dioxide:
BaCO 3 (s) → BaO(s) + CO 2 (g)
The compound occurs naturally as
the mineral witherite and can be prepared by adding an alkaline solution
of a carbonate to a solution of a barium salt. It is used as a raw material
for making other barium salts, as a
Ûux for ceramics, and as a raw material in the manufacture of certain
types of optical glass.
barium chloride A white compound, BaCl 2 . The anhydrous compound has two crystalline forms: an
α form (monoclinic; r.d. 3.856),
which transforms at 962°C to a β
form (cubic; r.d. 3.917; m.p. 963°C;
b.p. 1560°C). There is also a dihydrate, BaCl 2 .2H 2 O (cubic; r.d. 3.1),
which loses water at 113°C. It is prepared by dissolving barium carbonate
(witherite) in hydrochloric acid and
crystallizing out the dihydrate. The
compound is used in the extraction
of barium by electrolysis.
barium hydrogencarbonate (barium bicarbonate) A compound,
Ba(HCO 3 ) 2 , which is only stable in solution. It can be formed by the action
of carbon dioxide on a suspension of
barium carbonate in cold water:
BaCO 3 (s) + CO 2 (g) + H 2 O(l) →
Ba(HCO 3 ) 2 (aq)
On heating, this reaction is reversed.
barium hydroxide (baryta) A
white solid, Ba(OH) 2 , sparingly soluble in water. The common form is
the octahydrate, Ba(OH) 2 .8H 2 O; monoclinic; r.d. 2.18; m.p. 78°C. It can be
produced by adding water to barium
monoxide or by the action of sodium
hydroxide on soluble barium compounds and is used as a weak alkali
in volumetric analysis.
barium oxide A white or yellowish
solid, BaO, obtained by heating barium in oxygen or by the thermal decomposition of barium carbonate or
nitrate; cubic; r.d. 5.72; m.p. 1923°C;
b.p. 2000°C. When barium oxide is
heated in oxygen the peroxide, BaO 2 ,
is formed in a reversible reaction
that was once used as a method for
obtaining oxygen (the Brin process).
Barium oxide is now used in the
manufacture of lubricating-oil additives.
barium peroxide A dense offwhite solid, BaO 2 , prepared by carefully heating *barium oxide in
oxygen; r.d. 4.96; m.p. 450°C. It is
57
barium peroxide
b
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