NAME: RANSLEY FERNANDES ADMIN NO. 40202
UNIT 19: PRACTICAL CHEMICAL ANALYSIS
LEARNING AIM B: To investigate spectroscopic techniques to identify the compounds and to
determine the concentrations.
SPECTROSCOPIC TECHNIQUES
Ultraviolet/visible spectroscopy technique
Ultraviolet/visible spectroscopy is an
analytical technique in which light is passed
through a sample at a specific wavelength in
the ultraviolet or visible spectrum. This
spectroscopic technique is used to determine
the analyte concentrations or the chemical
conversion of the component in the solution.
The molecules that have bonding electrons
and non-bonding electron has the ability to
absorb energy in the form of
ultraviolet/visible light in order to stimulate
these electrons to greater anti-bonding
molecular orbitals. If the electrons are
stimulated more easily, it can absorb the
longer wavelength of light.
This is the ultraviolet/visible spectroscopic technique, in which the ray of light ultraviolet and/or
visible light source is spilt into its element wavelengths using a prism or diffraction grating. The
single wavelength beam in turn is divided into the 2 equal intensity beams with the use of half-
mirrored device. The sample beam (coloured magenta) goes through the cuvette, which is a small
see-through container; the cuvette has a solution in it which is being examined in transparent
solvent. The other beam, coloured blue, goes through an identical cuvette that has only solvent
present. Afterwards, the intensities of these beams are measured using electronic detectors and
then they are compared. The reference beam intensity which is coloured in blue will feel little or no
light absorption and because of it, it is described as Iₒ. The sample beam coloured in magenta, the
intensity is described as I. The spectrometers can automatically scan the wavelengths of all the
components, the ultraviolet section usually scanned is from 200 nm to 400 nm and the visible region
is from 400 nm to 800 nm.
The ultraviolet/visible spectroscopy includes the transitions of electron in the molecule or
ion from a lower energy level to higher energy level or the other way around by absorption
or emission of radiation in ultraviolet/visible range of the electromagnetic spectrum.
, NAME: RANSLEY FERNANDES ADMIN NO. 40202
Infrared spectroscopy
The visible light is created of different range of electromagnetic frequencies, the frequencies
can be observed in different colours. Similarly, the infrared radiation is made up of
continuous series of frequencies and the human eyes are unable to detect them.
When you flash different series of infrared frequencies one by one through a sample of an
organic compound, can observe some frequencies are being absorbed by the organic
compound. The detector present on the other side of the compound would show that some
infrared frequencies have gets through
the compound almost fully without losing,
however the other infrared frequencies
would intensely absorb. The percentage
transmittance is the measure of how
much the specific frequency will pass
through the compound. If the percentage
transmittance is 100, it means that all the
frequencies that were flashed gets
through the compound without getting
absorbed. If the percentage transmittance
is 5 that means that almost all the specific
frequency is absorbed by the compound.
When there is high absorbance, it can tell
us about the bonds present in the
compound.
For each frequency of light there is a particular energy. If the specific frequency is absorbed
by the compound then it means that the energy is being shifted to the compound. The
energies in infrared radiation corresponds to the energies involved in the bond vibrations.
The atoms in covalent bonds are not attached together by the rigid links; the two atoms are
joined together due to the both nuclei are attracted to the same pair of electrons. These
two nuclei can vibrate at any direction- it can vibrate forward and backward, towards and
away from one another.
The diagram indicates the stretching in carbon-
oxygen single bond (C-O). There are other atoms
joined to carbon and oxygen. For instance, this
carbon-oxygen single bond could be in methanol.
The energy in the vibration relies on factors like
the length of the bond and the mass of the
atoms at either ends- this means that each bond
different from the other will lead to vibrating in different manner, that will involve different
amounts of energy. The bonds vibrate at all times, however if you beam correct amount of
energy on bond, it can go into higher vibrational state. The energy required to do this differs
from bond to bond and therefore every different bond will absorb the different frequency of
infrared radiation.
UNIT 19: PRACTICAL CHEMICAL ANALYSIS
LEARNING AIM B: To investigate spectroscopic techniques to identify the compounds and to
determine the concentrations.
SPECTROSCOPIC TECHNIQUES
Ultraviolet/visible spectroscopy technique
Ultraviolet/visible spectroscopy is an
analytical technique in which light is passed
through a sample at a specific wavelength in
the ultraviolet or visible spectrum. This
spectroscopic technique is used to determine
the analyte concentrations or the chemical
conversion of the component in the solution.
The molecules that have bonding electrons
and non-bonding electron has the ability to
absorb energy in the form of
ultraviolet/visible light in order to stimulate
these electrons to greater anti-bonding
molecular orbitals. If the electrons are
stimulated more easily, it can absorb the
longer wavelength of light.
This is the ultraviolet/visible spectroscopic technique, in which the ray of light ultraviolet and/or
visible light source is spilt into its element wavelengths using a prism or diffraction grating. The
single wavelength beam in turn is divided into the 2 equal intensity beams with the use of half-
mirrored device. The sample beam (coloured magenta) goes through the cuvette, which is a small
see-through container; the cuvette has a solution in it which is being examined in transparent
solvent. The other beam, coloured blue, goes through an identical cuvette that has only solvent
present. Afterwards, the intensities of these beams are measured using electronic detectors and
then they are compared. The reference beam intensity which is coloured in blue will feel little or no
light absorption and because of it, it is described as Iₒ. The sample beam coloured in magenta, the
intensity is described as I. The spectrometers can automatically scan the wavelengths of all the
components, the ultraviolet section usually scanned is from 200 nm to 400 nm and the visible region
is from 400 nm to 800 nm.
The ultraviolet/visible spectroscopy includes the transitions of electron in the molecule or
ion from a lower energy level to higher energy level or the other way around by absorption
or emission of radiation in ultraviolet/visible range of the electromagnetic spectrum.
, NAME: RANSLEY FERNANDES ADMIN NO. 40202
Infrared spectroscopy
The visible light is created of different range of electromagnetic frequencies, the frequencies
can be observed in different colours. Similarly, the infrared radiation is made up of
continuous series of frequencies and the human eyes are unable to detect them.
When you flash different series of infrared frequencies one by one through a sample of an
organic compound, can observe some frequencies are being absorbed by the organic
compound. The detector present on the other side of the compound would show that some
infrared frequencies have gets through
the compound almost fully without losing,
however the other infrared frequencies
would intensely absorb. The percentage
transmittance is the measure of how
much the specific frequency will pass
through the compound. If the percentage
transmittance is 100, it means that all the
frequencies that were flashed gets
through the compound without getting
absorbed. If the percentage transmittance
is 5 that means that almost all the specific
frequency is absorbed by the compound.
When there is high absorbance, it can tell
us about the bonds present in the
compound.
For each frequency of light there is a particular energy. If the specific frequency is absorbed
by the compound then it means that the energy is being shifted to the compound. The
energies in infrared radiation corresponds to the energies involved in the bond vibrations.
The atoms in covalent bonds are not attached together by the rigid links; the two atoms are
joined together due to the both nuclei are attracted to the same pair of electrons. These
two nuclei can vibrate at any direction- it can vibrate forward and backward, towards and
away from one another.
The diagram indicates the stretching in carbon-
oxygen single bond (C-O). There are other atoms
joined to carbon and oxygen. For instance, this
carbon-oxygen single bond could be in methanol.
The energy in the vibration relies on factors like
the length of the bond and the mass of the
atoms at either ends- this means that each bond
different from the other will lead to vibrating in different manner, that will involve different
amounts of energy. The bonds vibrate at all times, however if you beam correct amount of
energy on bond, it can go into higher vibrational state. The energy required to do this differs
from bond to bond and therefore every different bond will absorb the different frequency of
infrared radiation.
