OPTION G: MODERN ANALYTICAL CHEMISTRY

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G.1 Analytical Techniques (2h)

 G.1.1. State the reasons for using analytical techniques.

• Analytical techniques are used in structure determination, analysis of composition of substances, and to determine purity. Students will be expected to have encountered the techniques in this option used in the above contexts.

G.1.2. Outline the information that can be obtained from analytical techniques, singly or in combination.

• 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 spectroscopy &endash; assaying of metal ions; organic structure determinations; detection of drug metabolites
• Infrared spectroscopy &endash; organic structure determinations; information on strengths of bonds, secondary structure of proteins, measuring degree of unsaturation of oils and fats.
• Mass spectrometry &endash; organic structure determinations. Gas chromatography-mass spectrometry (GC-MS) has important uses in drug and food testing. Mass spectrometry is also incorporated into some techniques for radioisotope dating.
• Chromatography &endash; primarily, chromatography is used for separating mixtures. Their components can then be identified by other techniques. For example, gas chromatography &endash; mass spectrometry (GC-MS) has important uses in drug and food testing and forensic science.

G.2 Principles of Spectroscopy (2h)

G.2.1. Describe the electromagnetic spectrum.

• X-ray, u.v, visible, i.r. and radio (including microwave) should be identified. The variation in wavelength, frequency and energy across the spectrum should be highlighted.

G.2.2. Distinguish between absorption and emission spectra and how each is produced.

G.2.3. Describe the atomic and molecular processes in which absorption of energy takes place.

• Relate to topic 12.2 for atomic spectra. Absorption 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 computer/Fourier transform.

G.3 Visible and Ultraviolet spectroscopy (4h)

 G.3.1. Describe the factors that affect the color of transition metal complexes.

• Colour should be explained in simple terms of presence of orbitals of appropriate energy and movement of d electrons between them. Students need not describe these orbitals.

G.3.2. Describe the effect of different ligands on the splitting of the d orbitals in transition metal complexes

G.3.3. State that organic molecules containing a double bond absorb UV radiation.

G.3.4. Describe the effect of the conjugation of double bonds in organic molecules on the wavelength of the absorbed light.

G.3.5 Predict whether or not a particular molecule will absorb UV or visible radiation.

G.3.6 State Beers-Lambert law

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 the absorption of infrared radiation by molecules.

• H₂O, -CH₂-, SO₂, CO₂ provide suitable examples. The change in bond polarity as an essential requirement should be stressed.

G.4.2. State the relationship between wavelength and wave number.

• Inverse, ie., the wave number is the number of wavelengths that make up one cm. High wave number implies high energy.

G.4.3. Deduce the functional groups in an organic molecule from its infrared spectrum.

• For up to three functional groups. It is not required to learn the characteristic absorption frequencies of functional groups, but students must be able to use correlation tables.

G.5. Nuclear magnetic resonance (NMR) spectroscopy (3h)

G.5.1. State that that atoms with an odd mass number can be detected by NMR spectroscopy

G.5.2 Analyze simple NMR spectra.

• Include number of peaks
• chemical shift with tetramethylsilane (TMS) as arbitrary standard
• area under each peak
• No treatment of spin-spin coupling constants is required but students should be familiar with splitting patterns for simple molecules, eg. iodoethane.

G.5.3. Outline how the principles of NMR can be extended to use in body scanners.

• Protons in water in human cells can be detected in a magnetic resonance scanner, 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 formula may be obtained from the molecular ion peak.

• Use the fact that modern spectrometers have sufficient accuracy to allow identification of the molecular formula from the molecular mass using the accurately known masses of the commonest isotopes of carbon, hydrogen, nitrogen and oxygen.

G.6.2. Analyze molecular mass spectra.

• Stress the importance of isotopes. Use of the (M + 2) and (M + 4) peaks for chlorine and bromine; recognition of molecular fragments.

G.7 Chromatography (4h)

G.7.1. Stated the reasons for using chromatography.

• Chromatography can be used to separate substances for analysis and to determine purity. The coupling of chromatography with other techniques should be highlighted where possible.

G.7.2. State that all chromatographic techniques require a stationary phase and a mobile phase.

• Components in a mixture have different tendencies to absorb on to a surface or dissolve in a solvent. This provides a powerful means of separating the components.

G.7.3. Explain how the phenomena absorption, partition, ion exchange and molecular exclusion can be used in chromatographic techniques.

• Each of these phenomena gives rise to different chromatographic techniques.

G.7.4. Outline the use of paper chromatography; thin-layer chromatography; column chromatography; ion exchange chromatography; gas-liquid chromatography; and high performance liquid chromatography. For each technique an outline of its operation is all that is required. Some can be carried out in the school laboratory.

G.7.5. Deduce which chromatographic technique is best to separate the components in a particular mixture. Simple examples only.