Emphasize problem solving and using the information gained from one or more techniques throughout this option. Students should understand the chemical principles behind each analytical technique but are not expected to have a detailed knowledge of the instruments themselves.
G.1 Analytical Techniques (2h)
G.1.1 State the reasons for using analytical
Analytical techniques are used in structure determination, in analysis of composition of substances and to
G.1.2 Outline the information that can be obtained
from analytical techniques, singly or in combination.
Students should be able to draw upon a range of contexts to illustrate the information obtained by using a
technique or range of techniques.
G.2 Principles of Spectroscopy (2h)
G.2.1 Describe the
X-ray, uv, visible, ir and radio (including microwave) should be identified. Highlight the variation in wavelength,
frequency and energy across the spectrum.
G.2.2 Distinguish between
absorption and emission spectra and how each is produced.
Cross reference with 2.2.1.
G.2.3 Describe the atomic and
molecular processes in which absorption of energy takes place.
Cross reference with 2.2. The description should cover vibrations, rotation and electronic transitions only.
G.2.4 Describe the operating
principles of a double-beam infrared spectrometer.
A schematic diagram of a simple double-beam spectrometer is sufficient. This example is chosen to illustrate the
general principles of how spectrometers operate. Mention could be made of modern methods of processing
signals by Fourier transformation.
G.3 Visible and Ultraviolet Spectroscopy (4h)
G.3.1 Describe the factors that affect the colour of
transition metal complexes.
Cross reference with 13.2.6. The factors are the identity of the metal (eg. Mn2-, Fe2+), oxidation number (eg
Fe2+, Fe3+) and the identity of the ligand. Limit this to octahedral complexes in aqueous solution.
G.3.2 Describe the effect of different ligands on the
splitting of the d orbitals in transition metal complexes.
The ligands should be limited to NH3, H2O and Cl-.
G.3.3 State that organic molecules containing a
double bond absorb ultraviolet radiation.
Refer to conjugated and delocalized systems : arenes, alkenes and natural products, eg chlorophyll.
G.3.4 Describe the effect of the conjugation of
double bonds in organic molecules on the wavelength of the absorbed light.
Retinol and phenolphthalein are suitable examples.
G.3.5 Predict whether or not a particular molecule will absorb ultraviolet or visible radiation.
G.3.6 State the Beer-Lambert law.
log10 = elc
G.3.7 Construct a calibration curve and use the Beer-Lambert law to determine the concentration of an unknown solution.
G.4 Infrared Spectroscopy (3h)
G.4.1 Describe what occurs at a molecular level
during absorption of infrared radiation by molecules.
H2O, -CH2-, SO2 and CO2 are suitable examples. Stress the change in bond polarity as the vibrations
(stretching and bending) occur.
G.4.2 State the relationship between wavelength and
An inverse relationship exists (ie. the wavenumber is the number of wavelengths that make up one cm). High
wavenumber implies high energy.
G.4.3 Deduce the functional groups in an organic
molecule from its infrared spectrum.
Examples should contain up to three functional groups. Students are not required to learn the characteristic
absorption frequencies of functional groups, but must be familiar with the relevant information in the data booklet.
The precise wavenumber of the absorption depends upon neighbouring atoms.
G.5 Nuclear Magnetic
G.5.1 State that atoms with an odd mass number can be detected by NMR spectroscopy.
G.5.2 Analyse simple NMR spectra.
The emphasis is on 1H spectra. Interpretation should include the :
G.5.3 Outline how NMR
is used in body scanners.
Protons in water in human cells can be detected by magnetic resonance imaging (MRI), giving a three-dimensional
view of organs in the human body.
G.6 Mass Spectrometry (3h)
G.6.1 Discuss how the molecular mass
and molecular formula of a compound may be obtained from the molecular ion
Spectrometers have sufficient accuracy to allow identification of the molecular formula from the molecular mass
using the masses of the commonest isotopes of C, H, N and O.
G.6.2 Analyse molecular mass spectra.
Stress the importance of isotopes and relate these to the (M + 1)+ peak for 13C and the (M + 2)+ and (M + 4)+
peaks for chlorine and bromine. Include recognition of molecular fragments (see 20.1.3).
G.7 Chromatography (4h)
G.7.1 State the reasons for using chromatography.
Chromatography can be used to separate substances for analysis and to determine purity. Highlight the coupling
of chromatography with other techniques.
G.7.2 State that all chromatographic
techniques require a stationary phase and a mobile phase.
Components in a mixture have different tendencies to adsorb onto a surface or dissolve in a solvent. This provides
a means of separating the components of a mixture.
G.7.3 Explain how the phenomena of adsorption
and partition can be used in chromatographic techniques.
Each of these phenomena gives rise to different chromatographic techniques. Molecular exclusion is not required.
G.7.4 Outline the use of paper chromatography,
thin-layer chromatography (TLC), column chromatography, gas-liquid
chromatography (GLC) and high performance liquid chromatography (HPLC).
An outline of the operation for each technique is all that is required. This should include an understanding of Rf
values where relevant.
G.7.5 Deduce which chromatographic technique is most appropriate for separating the components in a particular mixture.