per(II) acetate, is added to the test so-
lution and boiled. If any reducing
sugars are present a red precipitate
of copper(II) oxide is formed. The re-
action will be negative in the pres-
ence of disaccharide sugars as they
are weaker reducing agents.
barite See barytes.
bariumSymbol 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 bar-
ium 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 bar-
ium compounds are extremely poiso-
nous. It wasÜrst 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 carbonateA white insolu-
ble compound, BaCO 3 ; r.d. 4.43. It de-
composes on heating to give barium
oxide and carbon dioxide:
BaCO 3 (s) →BaO(s) + CO 2 (g)The compound occurs naturally as
the mineral witheriteand can be pre-
pared by adding an alkaline solution
of a carbonate to a solution of a bar-
ium salt. It is used as a raw material
for making other barium salts, as a
Ûux for ceramics, and as a raw ma-
terial in the manufacture of certain
types of optical glass.
barium chloride A white com-
pound, BaCl 2. The anhydrous com-
pound has two crystalline forms: an
αform (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 dihy-
drate, BaCl 2 .2H 2 O (cubic; r.d. 3.1),
which loses water at 113°C. It is pre-
pared 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 (bar-
ium bicarbonate)A compound,
Ba(HCO 3 ) 2 , which is only stable in so-
lution. 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 solu-
ble in water. The common form is
the octahydrate, Ba(OH) 2 .8H 2 O; mon-
oclinic; 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 com-
pounds and is used as a weak alkali
in volumetric analysis.barium oxideA white or yellowish
solid, BaO, obtained by heating bar-
ium in oxygen or by the thermal de-
composition 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 addi-
tives.barium peroxide A dense off-
white solid, BaO 2 , prepared by care-
fully heating *barium oxide in
oxygen; r.d. 4.96; m.p. 450°C. It is57 barium peroxide
b