the surface of the earth and in the
atmosphere as a result of cosmic
radiation and the presence of radioisotopes in the earth’s rocks, soil,
and atmosphere. The radioisotopes
are either natural or the result of nuclear fallout or waste gas from power
stations. Background counts must be
taken into account when measuring
the radiation produced by a speciÜed
source.
back titration A technique in *volumetric analysis in which a known
excess amount of a reagent is added
to the solution to be estimated. The
unreacted amount of the added
reagent is then determined by titration, allowing the amount of substance in the original test solution to
be calculated.
bacteriocidal Capable of killing
bacteria. Common bacteriocides are
some antibiotics, antiseptics, and disinfectants.
bacteriorhodopsin A membranebound protein of the halophilic (saltresistant) bacterium Halobacterium
halobium. When activated by light, it
pumps protons out of the cell; this
creates a concentration gradient,
which enables ATP to be synthesized.
Bacteriorhodopsin is composed of
seven α-helix segments, which span
the membrane and are joined together by short amino-acid chains. It
contains the prosthetic group retinal,
which is also found in the pigment
rhodopsin in the rod cells of vertebrates.
Baeyer, Adolf von (1835–1917)
German organic chemist noted for
his work on organic synthesis. He
synthesized and determined the
structure of indigo and also synthesized some of the Ürst barbiturates.
In his work on carbon rings he formulated his strain theory. Bayer was
awarded the 1905 Nobel Prize for
chemistry.
Baeyer strain See angle strain.
Baeyer test A test for unsaturated
compounds in which potassium permanganate is used. Alkenes, for example, are oxidised to glycols, and
the permanganate loses its colour:
3R 2 C=CR 2 + 2KMnO 4 + 4H 2 O →
2MnO 2 + 2KOH + 3R 2 COHR 2 COH
Baeyer–Villiger reaction A rearrangement reaction, sometimes
known as the Dakin reaction, commonly used in organic synthesis in
which a ketone reacts with a peroxy
acid to form an ester. For example,
R–CO–R → R–CO–O–R
The reaction is equivalent to the insertion of an oxygen atom next to
the ketone’s carbonyl (>C=O) group.
Meta-chloroperbenzoic acid (m-CPBA;
ClC 6 H 4 .CO.O.OH) and triÛuoroperethanoic acid (CF 3 .CO.O.OH) are
typical peroxy acids employed in the
reaction. It was discovered by Adolf
von *Baeyer and the German
chemist V. Villiger in 1899.
Bakelite A trade name for certain
*phenol–formaldehyde resins, Ürst
introduced in 1909 by the Belgian–
US chemist Leo Hendrik Baekeland
(1863–1944).
baking powder A mixture of powdered compounds added to dough or
cake mixture to make it rise in cooking. It is used as a substitute for yeast
in bread-making. Baking powders
consist of a source of carbon dioxide,
such as sodium hydrogencarbonate
or ammonium hydrogencarbonate,
and an acidic substance such as calcium hydrogenphosphate, potassium
hydrogentartrate (cream of tartar), or
sodium hydrogenphosphate. In the
hot wet mixture, the acid releases
bubbles of carbon dioxide gas from
55
baking powder
b
www.AzShimi.ir www.AzShimi.com
atmosphere as a result of cosmic
radiation and the presence of radioisotopes in the earth’s rocks, soil,
and atmosphere. The radioisotopes
are either natural or the result of nuclear fallout or waste gas from power
stations. Background counts must be
taken into account when measuring
the radiation produced by a speciÜed
source.
back titration A technique in *volumetric analysis in which a known
excess amount of a reagent is added
to the solution to be estimated. The
unreacted amount of the added
reagent is then determined by titration, allowing the amount of substance in the original test solution to
be calculated.
bacteriocidal Capable of killing
bacteria. Common bacteriocides are
some antibiotics, antiseptics, and disinfectants.
bacteriorhodopsin A membranebound protein of the halophilic (saltresistant) bacterium Halobacterium
halobium. When activated by light, it
pumps protons out of the cell; this
creates a concentration gradient,
which enables ATP to be synthesized.
Bacteriorhodopsin is composed of
seven α-helix segments, which span
the membrane and are joined together by short amino-acid chains. It
contains the prosthetic group retinal,
which is also found in the pigment
rhodopsin in the rod cells of vertebrates.
Baeyer, Adolf von (1835–1917)
German organic chemist noted for
his work on organic synthesis. He
synthesized and determined the
structure of indigo and also synthesized some of the Ürst barbiturates.
In his work on carbon rings he formulated his strain theory. Bayer was
awarded the 1905 Nobel Prize for
chemistry.
Baeyer strain See angle strain.
Baeyer test A test for unsaturated
compounds in which potassium permanganate is used. Alkenes, for example, are oxidised to glycols, and
the permanganate loses its colour:
3R 2 C=CR 2 + 2KMnO 4 + 4H 2 O →
2MnO 2 + 2KOH + 3R 2 COHR 2 COH
Baeyer–Villiger reaction A rearrangement reaction, sometimes
known as the Dakin reaction, commonly used in organic synthesis in
which a ketone reacts with a peroxy
acid to form an ester. For example,
R–CO–R → R–CO–O–R
The reaction is equivalent to the insertion of an oxygen atom next to
the ketone’s carbonyl (>C=O) group.
Meta-chloroperbenzoic acid (m-CPBA;
ClC 6 H 4 .CO.O.OH) and triÛuoroperethanoic acid (CF 3 .CO.O.OH) are
typical peroxy acids employed in the
reaction. It was discovered by Adolf
von *Baeyer and the German
chemist V. Villiger in 1899.
Bakelite A trade name for certain
*phenol–formaldehyde resins, Ürst
introduced in 1909 by the Belgian–
US chemist Leo Hendrik Baekeland
(1863–1944).
baking powder A mixture of powdered compounds added to dough or
cake mixture to make it rise in cooking. It is used as a substitute for yeast
in bread-making. Baking powders
consist of a source of carbon dioxide,
such as sodium hydrogencarbonate
or ammonium hydrogencarbonate,
and an acidic substance such as calcium hydrogenphosphate, potassium
hydrogentartrate (cream of tartar), or
sodium hydrogenphosphate. In the
hot wet mixture, the acid releases
bubbles of carbon dioxide gas from
55
baking powder
b
www.AzShimi.ir www.AzShimi.com