Option G : Modern Analytical Chemistry

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 techniques.
                    Analytical techniques are used in structure determination, in analysis of composition of substances and to
                    determine purity.

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.
 

  •                 Visible and ultraviolet (uv) spectroscopy - assaying of metal ions, organic structure determination and detection of
  •                 drug metabolites
  •                 Infrared (ir) spectroscopy - organic structure determination, information on strengths of bond, secondary structure
  •                 of proteins and measuring degree of unsaturation of oils and fats
  •                 Mass spectrometry - organic structure determination and isotopic dating (eg 14C dating)
  •                 Gas chromatography-mass spectrometry (GC-MS) - drug and food testing and forensic science


    G.2           Principles of Spectroscopy (2h)

    G.2.1         Describe the electromagnetic spectrum.
                            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 wavenumber.
                        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 Resonance (NMR)
                    Spectroscopy (4h)

    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 :

  •                 number of peaks
  •                 chemical shift (with tetramethylsilane (TMS) as the reference standard)
  •                 area under each peak
  •                 splitting patterns (treatment of spin-spin coupling constants is not required, but students should be familiar with
  •                 splitting patterns for simple molecules ie doublet, triplet and quartet).

    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 peak.
                        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.

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