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Worksheet 12.1
Chapter 12: Modern analytical chemistry – glossary
Absorbance (A) The ratio of log10 (I0/I) where Io is the intensity of light transmitted through a
reference and I is the intensity of light transmitted through a solution. A = log10 (Io/I).
Absorption spectrum A spectrum produced when a species absorbs a photon of electromagnetic
radiation and moves from a lower energy level to higher energy level.
Acceleration The stage in a mass spectrometer when the positive ions are attracted to negatively
charged plates. They are accelerated by an electric field.
Adsorption The process, usually temporarily, when gases, liquids or solutes bond on the surface of a
solid or liquid, through weak intermolecular forces.
Analyte A sample component whose concentration is being measured (i.e. analyzed).
Atomizer Part of the atomic absorption spectrometer where the spray of the sample solution is mixed
with the fuel (e.g. C2H2) and air, and carried into the flame. The solvent evaporates and gaseous atoms
are formed.
Beer–Lambert Law The absorbance (A) of a given wavelength (λ) of light by a dilute solution is
proportional to its concentration (c). A = log10 (Io/I) = εcl. ε is molar absorptivity, c is concentration and
l is the length of the radiation through the substance.
Calibration A quantitative procedure which relates the known concentration of standard solutions to
a property, such as absorbance of light of particular wavelength.
Calibration curve A graph which shows the relationship between properties such as absorbance and
concentration. This is a linear relationship, under conditions that obey Beer’s Law:
A = log10 (Io/I) = εcl.
Capillary action This occurs when a liquid spontaneously rises in a narrow space such as a thin tube,
or in porous materials such as paper. It occurs because of intermolecular attractive forces between the
liquid and solid surrounding surfaces.
Chemical environment The chemical environment refers to the number and types of atoms a
particular atom is bonded to within a molecule.
Chemical shift (δ) The frequency of a resonance (f) in the NMR spectrum relative to a standard (f0),
such as TMS (tetramethylsilane). δ = ((f – f0)/f0)  106 ppm.
Chromatogram
A record obtained from chromatography.
Chromatography A technique for analyzing or separating mixtures of gases, liquids, or dissolved
substances based on the differential solubility/adsorption between two phases.
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Colorimeter A device for measuring the concentration of coloured substances in solution by passing
visible light through the coloured substance.
Column chromatography A chromatographic technique in which the components are separated with
a suitable solvent or solvent mixture. The mixture is passed through a column packed with an adsorbent
material such as silica or alumina. The tap at the bottom is initially closed to allow the column to be
saturated with solvent. The sample to be separated is dissolved in a minimum volume of solvent and
added to the column from the top. Fresh solvent is added in the same way to wash the sample down the
stationary phase and the tap at the bottom is now opened. The different components are separated as
they pass through the column at different rates and collected at the bottom as different fractions.
Combustion analysis A method for determining the empirical formula of a compound which is
based on the masses of reactants and products during complete combustion.
Complementary colours
Colours which when mixed together produce white light.
Conjugated molecules Conjugated molecules have double or triple bonds separated by one single
bond. The π electrons are delocalized between the atoms which form π bonds.
Continuous spectrum
An emission spectrum with all the wavelengths or frequencies of visible light.
Deflection The stage in a mass spectrometer where the accelerated positive ions are deflected by a
magnetic field placed at right angles to their path. The amount of deflection is proportional to the
charge/mass ratio. Ions with smaller mass are deflected more than heavier ions. Ions with higher
charges have greater deflections; they interact more effectively with the magnetic field.
Degenerate orbitals
Orbitals which have the same energy.
Detection (in a mass spectrometer) The stage where the number of positive ions with a particular
charge/mass ratio is measured and recorded.
Detection limit
The minimum amount of a sample that can be detected when analyzed.
Double-beam spectrometry A spectroscopic method in which one beam is passed through the
sample under investigation and the other through a reference sample.
Electromagnetic wave A wave of oscillating electric and magnetic fields that can move through a
vacuum with the speed of light (c).
Electromagnetic spectrum The range of electromagnetic radiation or waves including, in order of
decreasing frequency, γ rays, X-rays, UV radiation, visible light, IR radiation, microwaves and radio
waves. (See Table 3 of the IB Data booklet).
Electron bombardment The process of forming positive ions from atoms (and molecules) in a mass
spectrometer by bombarding them with electrons of high kinetic energy. The colliding electron ejects
an electron from an outer energy (valence) level and both electrons leave the atom:
X(g) + e– → X–(g) +2e–.
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Electron transition The movement of electrons from one orbital to another. A transition from a
higher to a lower energy level produces an emission spectrum. A transition from a lower to higher
energy level produces an absorption spectrum.
Elution The process of removing an absorbed material (the adsorbate) from an adsorbent by washing
it with a liquid (the eluent). The solution consisting of the adsorbate dissolved in the eluent is the
eluate.
Emission spectrum An emission spectrum is produced when an excited atom or molecule moves
from a higher to a lower level with the emission of electromagnetic radiation.
Empirical formula This gives the ratio of the atoms of different elements in a compound. It is the
molecular formula expressed as its simplest ratio. The molecular formula is a whole-number multiple
of the empirical formula.
Energy levels The allowed energies of electrons in an atom (or molecule). Electrons fill the lower
energy levels, or shells, closest to the nucleus, before occupying higher levels further from the nucleus.
Excited state The state of an atom or molecule when it is raised to a higher energy level above the
stable ground state.
Fingerprint region The region of the infrared spectrum of a substance approximately between 500
and 1500 cm–1. This region contains a very complicated series of absorptions that can be used to
identify an unknown compound. The absorptions are mainly due to different bending vibrational modes
within the molecule.
Frequency
The number of complete waves passing a point per second.
Gamma waves/radiation (or rays) High energy electromagnetic radiation of high frequency/short
wavelength emitted by changes in the nuclei of atoms.
Gel
A colloidal suspension of a solid dispersed in a liquid.
Ground state
The state of a species with lowest energy.
Immiscible liquids
Liquids which do not mix (e.g. water and hexane).
Infrared active vibrational modes These are vibrational modes which absorb infrared radiation, as
they result in a change in a dipole moment of the molecule.
Infrared radiation Infrared radiation (typical wavelength 10–4 m) lies between the visible and
microwave regions of the electromagnetic spectrum. It is absorbed by certain bonds, causing them to
stretch or bend, and gives information about the bonds in a molecule.
Integrated trace Part of the NMR spectrum which indicates the relative number of hydrogen atoms
in the different environments.
Ionization (in a mass spectrometer) The stage where gaseous atoms or molecules are hit with high
energy electrons to knock out electrons and produce positively charged ions: The atom or molecules
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are bombarded with electrons of high kinetic energy which ejects an electron from an outer energy
(valence) level. Both electrons leave the atom: X(g) + e– → X–(g) +2e–.
Line spectrum A line spectrum is an emission spectrum with only certain frequencies. It is produced
by excited atoms and ions as they fall back to a lower energy level.
Low resolution 1H NMR In low resolution NMR spectrum the number of peaks indicates the
number of different environments of hydrogen atoms and the chemical shifts give information about
the type of environment.
Magnetic resonance imaging (MRI) The use of a nuclear magnetic resonance spectrometer to
produce a two- or three-dimensional image of organs in the human body. Different parts of the body
have different water-lipid ratios in the tissue and therefore absorb radio waves at different frequencies.
The patient is placed in a strong magnetic field chamber and bombarded with pulses of radio waves.
Mass spectrometer An instrument in which gaseous atoms or molecules are ionized, accelerated by
an electric field and then deflected by a magnetic field. The amount of deflections depends on the
charge/mass of the positive ion.
Mass spectrometry This can be used to analyze the isotopic abundances of an element or the
molecular structure of a compound. It can also be used to determine the relative atomic mass of an
element or the relative molecular mass of a compound.
Mass spectrum The output plot from the mass spectrometer. It is a bar graph with abundance on the
vertical axis and mass/charge ratio on the horizontal axis.
Microwaves They have wavelengths that can be measured in centimeters and excite the rotational
motion of molecules. They give information about bond lengths of molecules. You do not need to
know the details at this level.
Miscible liquids
Liquids which do mix (e.g. water and ethanol).
Mobile phase A liquid or gas which moves through or along the stationary phase during
chromatography.
Molar absorptivity/Molar extinction coefficient
in cm) and per unit concentration (mol dm–3).
Absorbance of light per unit path length (usually
Molecular/parent ion This is formed in a mass spectrometer when a molecule loses one electron but
otherwise remains unchanged.
Monochromatic radiation
Electromagnetic radiation with a single wavelength.
Nuclear magnetic resonance The absorption of radio waves by nuclei such as 1H or 13C when
placed in an external magnetic field.
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Paper chromatography A chromatographic technique which uses very absorbent paper. The
stationary phase is the water attached to the paper and the mobile phase is a suitable liquid solvent or
mixture of solvents.
Partition
The distribution of a solute between two immiscible solvents.
Percentage composition
The percentage, by mass, of each element in a compound.
Phase A homogeneous part of a system that is physically distinct. It is separated from other parts by a
boundary.
Phenolphthalein A common acid–base indicator used for strong acid/strong base and weak
acid/strong base titrations. It is colourless in acid solution; pink in alkaline solution.
Photon A ‘packet’ or quantum of electromagnetic radiation. The energy of the photon (Ephoton) is
related to the frequency (f) of the radiation by Planck’s equation.
Planck’s equation Ephoton= hf (The equation is given in Table 1 of the IB Data booklet). h is Planck’s
constant (Its value is given in Table 2 of the IB Data booklet).
Promotion
The movement of an electron from a lower energy level to a higher energy level.
Qualitative analysis
Analysis used to determine the nature of the components in a substance.
Quantitative analysis Analysis used to determine the amount of each component in a substance.
Radiation The transmission of energy by means of an electromagnetic wave; or the emission of
particles from the nucleus of a decaying atom.
Radio waves Radio waves have the longest wavelengths in the electromagnetic spectrum with typical
wavelengths of 102 m. Radio waves can be absorbed by certain nuclei (usually 11 H ) causing them to
reverse their spin. They are used in NMR to give information about the chemical environment of
hydrogen nuclei.
Retention factor (Rf value) The retention factor (Rf) is defined as the distance travelled by the
compound divided by the distance travelled by the solvent front. Rf = distance moved by component
above the base line/distance moved by solvent front.
Solubility
The amount of solute required to form a saturated solution in a given volume of solvent.
Solute The solid, liquid or gas that has been dissolved to form a solution.
Solution
A solution is formed when a solid, liquid or gas is dissolved into a solvent.
Solvation The process of the solute particles dissolving in a solvent as they spread out and are
surrounded by solvent molecules.
Solvent
A solvent is a liquid that dissolves solids, liquids or gases to form a solution.
Solvent front
The maximum distance moved by the solvent in paper chromatography.
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Spectral line
molecule.
A particular wavelength/frequency of light emitted (or absorbed) by an atom, ion or
Spectroscopy
The production and analysis of spectra.
Stationary phase One of the two phases in chromatography. It can be a solid, a gel or a liquid
(sometimes distributed on a solid). The liquid may also be chemically bonded to the solid (bonded
phase) or immobilized onto it (immobilized phase).
Sunscreen
Support
A chemical that protects the skin from harmful ultraviolet radiation from the sun.
An inert material that carries the stationary phase in chromatography.
Tetramethylsilane (TMS)
Si(CH3)4. A reference standard for 1H NMR.
Thin-layer chromatography (TLC) A chromatographic technique in which compounds are
separated by a suitable solvent or solvent mixture on a thin layer of adsorbent material coated onto a
flat support.
Transmittance A measure of the extent to which a substance absorbs electromagnetic radiation of a
particular wavelength. Radiation which is not absorbed has 100 % transmittance. It is measured in a
spectrometer or colorimeter.
Vaporization of sample The first stage in a mass spectrometer in which a vaporized sample is
injected into the instrument. This allows the individual atoms/molecules of the sample to be analyzed.
Vibrational modes A molecule can vibrate in many ways. Each way is called a vibrational mode.
Examples include: the symmetric or asymmetric stretch and the symmetric and asymmetric bend. For a
vibrational mode to be IR active it must result in a change in a dipole moment of the molecule.
Wavelength
The distance between the peaks (or troughs) of one complete wave.
Wave number The reciprocal of the wavelength of a wave. When used in infrared spectroscopy it is
the number of complete waves in 1 cm and has units cm–1.
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