contaminants for use in chemical
analyses.
analyser A device, used in the *polarization of light, that is placed in
the eyepiece of a *polarimeter to observe plane-polarized light. The
analyser, which may be a *Nicol
prism or *Polaroid, can be oriented
in different directions to investigate
in which plane an incoming wave is
polarized or if the light is plane polarized. If there is one direction from
which light does not emerge from
the analyser when it is rotated, the
incoming wave is plane polarized. If
the analyser is horizontal when extinction of light takes place, the polarization of light must have been in
the vertical plane. The intensity of a
beam of light transmitted through an
analyser is proportional to cos
2
θ,
where θ is the angle between the
plane of polarization and the plane
of the analyser. Extinction is said to
be produced by ‘crossing’ the *polarizer and analyser.
analysis The determination of the
components in a chemical sample.
Qualitative analysis involves determining the nature of a pure unknown compound or the compounds
present in a mixture. Various chemical tests exist for different elements
or types of compound, and systematic analytical procedures can be
used for mixtures. Quantitative
analysis involves measuring the proportions of known components in a
mixture. Chemical techniques for
this fall into two main classes: *volumetric analysis and *gravimetric
analysis. In addition, there are numerous physical methods of qualitative
and quantitative analysis, including
spectroscopic techniques, mass spectrometry, polarography, chromatography, activation analysis, etc.
analyser
36
a
anchimeric assistance See neighbouring-group participation.
Andrews titration A titration
used to estimate amounts of reducing agents. The reducing agent being
estimated is dissolved in concentrated hydrochloric acid and titrated
with a solution of potassium iodate.
A drop of tetrachloromethane is
added to the solution. The end point
of the titration is reached when the
iodine colour disappears from this
layer. This is due to the reducing
agent being oxidized and the iodate
being reduced to ICl. This reaction involves a four-electron change.
ANFO Ammonium nitrate–fuel oil.
A mixture used extensively as a blasting agent in mining and quarrying.
The proportions are approximately
94% ammonium nitrate and 6% fuel
oil. ANFO has been used in terrorist
attacks (e.g. an attack on the Murrah
Federal Building, Oklahoma City, in
1995).
angle-resolved photoelectron
spectroscopy (ARPES) A technique
for studying the composition and
structure of surfaces by measuring
both the kinetic energy and angular
distribution of photoelectrons
ejected from a surface by electromagnetic radiation. See also photoelectron spectroscopy.
anglesite A mineral form of
*lead(II) sulphate, PbSO 4 .
angle strain The departure of a
bond angle from its normal value.
The effects of angle strain are often
apparent in aliphatic ring compounds. For example, in cyclopentane, C 5 H 10 , the angles between the
bonds of the ring differ from the normal tetrahedral angle (109° 28′),
which is found in cyclohexane. This
ring form of angle strain is often
called Baeyer strain.
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analyses.
analyser A device, used in the *polarization of light, that is placed in
the eyepiece of a *polarimeter to observe plane-polarized light. The
analyser, which may be a *Nicol
prism or *Polaroid, can be oriented
in different directions to investigate
in which plane an incoming wave is
polarized or if the light is plane polarized. If there is one direction from
which light does not emerge from
the analyser when it is rotated, the
incoming wave is plane polarized. If
the analyser is horizontal when extinction of light takes place, the polarization of light must have been in
the vertical plane. The intensity of a
beam of light transmitted through an
analyser is proportional to cos
2
θ,
where θ is the angle between the
plane of polarization and the plane
of the analyser. Extinction is said to
be produced by ‘crossing’ the *polarizer and analyser.
analysis The determination of the
components in a chemical sample.
Qualitative analysis involves determining the nature of a pure unknown compound or the compounds
present in a mixture. Various chemical tests exist for different elements
or types of compound, and systematic analytical procedures can be
used for mixtures. Quantitative
analysis involves measuring the proportions of known components in a
mixture. Chemical techniques for
this fall into two main classes: *volumetric analysis and *gravimetric
analysis. In addition, there are numerous physical methods of qualitative
and quantitative analysis, including
spectroscopic techniques, mass spectrometry, polarography, chromatography, activation analysis, etc.
analyser
36
a
anchimeric assistance See neighbouring-group participation.
Andrews titration A titration
used to estimate amounts of reducing agents. The reducing agent being
estimated is dissolved in concentrated hydrochloric acid and titrated
with a solution of potassium iodate.
A drop of tetrachloromethane is
added to the solution. The end point
of the titration is reached when the
iodine colour disappears from this
layer. This is due to the reducing
agent being oxidized and the iodate
being reduced to ICl. This reaction involves a four-electron change.
ANFO Ammonium nitrate–fuel oil.
A mixture used extensively as a blasting agent in mining and quarrying.
The proportions are approximately
94% ammonium nitrate and 6% fuel
oil. ANFO has been used in terrorist
attacks (e.g. an attack on the Murrah
Federal Building, Oklahoma City, in
1995).
angle-resolved photoelectron
spectroscopy (ARPES) A technique
for studying the composition and
structure of surfaces by measuring
both the kinetic energy and angular
distribution of photoelectrons
ejected from a surface by electromagnetic radiation. See also photoelectron spectroscopy.
anglesite A mineral form of
*lead(II) sulphate, PbSO 4 .
angle strain The departure of a
bond angle from its normal value.
The effects of angle strain are often
apparent in aliphatic ring compounds. For example, in cyclopentane, C 5 H 10 , the angles between the
bonds of the ring differ from the normal tetrahedral angle (109° 28′),
which is found in cyclohexane. This
ring form of angle strain is often
called Baeyer strain.
www.AzShimi.ir www.AzShimi.com