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Date Created: 07/08/14
Option A Modern Analytical Chemistry A1 Analytical Techniques A11 State the reasons for using analytical techniques 0 Forensics analysis of food products environment etc 0 Qualitative the presence of a substance eg forbidden substance in food 0 Quantitative amount of substance eg toxins in water A12 State that the structure of a compound can be determined by using information from a variety of analytical techniques singularly or in combination 0 Combination of instruments and techniques are used to obtain a complete picture of the chemical composition and structure of a substance A2 Principles of Spectroscopy A21 Describe the electromagnetic spectrum 0 Spectroscopy the way absorption or emission of electromagnetic radiation by substances varies with frequency 0 Electromagnetic spectrum waves travel at the same speed through a vacuum c300x108 ms391 cf7 Ehf 0 yrays effect on nucleus not used in analytical chemistry 0 Xrays effects inner equot leads to a diffraction pattern and information on atomic structure Xray diffraction crystallography 0 UV and Visible radiation affects valence electrons information about atomic structure 0 Infrared IR increases vibrations in particles and hence has an effect on bonds information about bonds in molecules 0 Microwaves increase rotational energy information about bond length 0 Radio waves alter the spin of nuclei when exposed to a magnetic field information about environment of atoms used in NMR A22 Distinguish between absorption and emission spectra and how each is produced 0 Emission spectroscopy frequency of the radiation emitted by excited particles dropping to a lower energy state is studied 0 Absorption spectroscopy radiation of a wide range of frequencies is passed through the sample and the intensity of the radiation of various frequencies emerging on the other side is compared to that going in to find out which frequencies are absorbed by the sample absorption of light in the visible range that makes things colored A3 Infrared IR Spectroscopy A31 Describe the operating principles of a double beam spectrometer 0 Radiation from source split into two equal beams that pass along parallel paths 0 Sample placed in one beam other is a reference containing same solvent and cell but without the sample 0 Light from the source passes through a monochromator which only allows radiation of a particular wavelength to pass through it 0 Radiation then strikes a beamsplitter which splits the radiation into two equal beams 0 Beams pass through the sample and reference and are recombined at the detector 0 Detector compares electronically both beams to see if any radiation was absorbed by the sample 0 Spectrum can be compared to a data bank to identify the compound A32 Describe how information from an IR spectrum can be used to identify bonds 0 Infrared region extends from 600cm391 to 4000cm391 0 Bonds can either stretch if diatomic or bend if more complex structure 0 Wavenumbers at which these motions absorb infrared radiation are shown in the spectrum 0 In IR wavenumber is used rather than frequency 1wavelength A33 Explain what occurs at a molecular level during the absorption of IR radiation by molecules 0 To absorb infrared light a vibrational motion must result in a change of the dipole moment of the molecule 0 Diatomic molecules of only one element such as 02 do not absorb infrared radiation as they are not polar molecules 0 Peak on the graph seen when dipole is changed A34 Analyse IR spectra of organic compounds up to three functional groups 0 Peaks used to identify functional groups 0 5001500 is the fingerprint region specific to a compound must be compared to a database to identify the compound A4 Mass Spectrometry A41 Determine the molecular mass of a compound from the molecular ion peak 0 In a mass spectrometer gaseous molecules are converted to positive ions and these ions after being accelerated through an electric field are deflected by a magnetic field 0 The lower the mass of the ion the greater the deflection 0 Ion with the greatest mass will correspond to a molecule that has only lost one electron the compound that was originally put in the spectrometer A42 Analyse fragmentation patterns in a mass spectrum to find the structure of a compound 0 The molecules that pass through a mass spectrometer fragment 0 These fragments are also ionized and the resulting ions detected A5 Nuclear Magnetic Resonance NMR Spectroscopy A51 Deduce the structure of a compound given information from its 1H NMR spectrum 0 As a result of changes that happen in the nucleus atoms with an odd mass number when placed in a strong magnetic field absorb radiation of radio frequency 0 Frequency varies slightly with the electron density around the nucleus and hence depends on its chemical environment 0 Most commonly applied to hydrogen atoms in a molecule 0 Integration trace shows the ratio of hydrogen atoms for each frequency A52 Outline how NMR is used in body scanners 0 Same technique as NMR 0 Renamed to remove nuclear from the title 0 Patient in a strong magnetic field and bombarded with radio waves 0 Signal detected and sent to computer an image is produced 0 Noninvasive 0 Shows soft tissues such as brain 0 Used to investigate infections and tumors A6 Atomic Absorption AA Spectroscopy A61 State the uses of Atomic Absorption spectroscopy 0 Used to detect metals in a variety of substances such as water blood and soil 0 Requires a very small amount of the sample and the metal does not need to be separated advantages 0 Very sensitive method can detect parts per million A62 Describe the principles of atomic absorption 0 Technique is based on the fact that when metal atoms are excited by heat they absorb light 0 Each metal absorbs at a characteristic frequency 0 The ratio of the intensity of the transmitted light to that of the incident light energy is proportional to the concentration of the metal atoms present 0 Calibration curves obtained by using standard solutions of known concentrations can be used to determine the concentration of the unknown sample A63 Describe the use of each of the following components of the Atomic Absorption spectrometer fuel atomizer monochromatic light source monochromatic detector readout 0 Atomic absorption relies on the fact metal atoms will absorb light of the same frequency as that emitted by excited atoms of that metal 0 Fuel injected with air and sample to produce long narrow high temperature flame ZOOOK 0 Atomizer flameheat evaporates solvent and breaks down compounds metal atoms absorb light 0 Monochromatic light source contains the metal that is being detected set so max frequency for the metal is emitted 0 Monochromatic detector measures for intensity of light A64 Determine the concentration of a solution from a calibration curve 0 Intensity of the absorption varies with conditions so instrument must be calibrated using solutions of known concentration 0 Graph drawn can then be used to determine the concentration of the unknown sample being analysed A7 Chromatography A71 State the reasons for using chromatography 0 Used to separate and identify components from a mixture 0 Qualitative analysis rather than a quantitative analysis A72 Explain that all chromatographic techniques involve adsorption on a stationary phase and partition between a stationary and a mobile phase 0 Components have different affinities for two phases 0 stationary phase component with strong affinity for this phase will be held back 0 mobile phase component with strong affinity for this phase will move quickly 0 Partition Chromatography o Stationary phase nonvolatile liquid held on an inert solid surface 0 Mobile phase liquid 0 Paper chromatography and GLC are examples 0 Adsorption Chromatography o Stationary phase solid 0 Mobile phase liquid or gas 0 Thinlayer chromatography is an example A73 Outline the use of paper chromatography thinlayer chromatography TLC and column chromatography 0 Paper chromatography 0 Separate colored components in ink or different amino acids 0 Stationary phase paper contains about 10 water 0 Mobile phase liquid solvent such as ethanol or water 0 Thinlayer chromatography TLC 0 Similar to paper chromatography 0 Stationary phase thin layer usually silica or alumina on a glass or plastic support 0 Mobile phase liquid solvent 0 Column chromatography TLC on a large scale Stationary phase silica or alumina saturated with solvent Mobile phase solvent eluent Fractions collected OOO A8 Visible and Ultraviolet Spectroscopy HL A81 Describe the effect of different ligands on the splitting of the dorbitals in transition metal complexes 0 Difference in energy between the sublevels of dorbitals corresponds to different wavelengths of visible light 0 When visible light is passed through the substances some wavelengths are absorbed A82 Describe the factors that affect the color of transition metal complexes 0 Charge on metal ion 0 Nature of ligand 0 Spectrochemical series 0 Geometry A83 State that organic molecules containing a double bond absorb radiation 0 Organic molecules with a double bond adsorb radiation A84 Describe the effect of the conjugation of double bonds in organic molecules on the wavelength of the absorbed light 0 Hybridisation some orbitals are filled some unfilled 0 Energy difference between the highest filled orbital and the lowest filled orbital corresponds to the UVVis region 0 Delocalisation also has an effect on energy difference between molecular orbitals alternate single and double bonds delocalization bonds A85 Predict whether or not a particular molecule will absorb ultraviolet or visible radiation 0 short UV light sigma bonds only 0 mid UV region isolated double bonds 0 longer UV single and double bonds are alternate 0 Vis only when there are delocalized bonds and conjugated double bonds A86 Determine the concentration of a solution from a calibration curve using the BeerLambert law 0 Calibration curve using known concentrations such as in atomic absorption A9 Nuclear Magnetic Resonance NMR Spectroscopy HL A91 Explain the use of tetramethylsilane TMS as reference standard 0 Reference standard in NMR 0 12 equivalent H atoms 0 Si has an influence on the frequency absorbed different from other Ccontaining compounds no overlap 0 Soluble and easy to remove A92 Analyse 1H NMR spectra 0 Splitting of peaks occurs as the magnetic field of a nuclei is affected by the magnetic field of neighboring protons in the methyl group 0 Effect known as spinspin coupling 0 Precise frequency of absorption is influenced by the direction of the magnetic field of any hydrogens attached to the neighboring carbon atoms 0 Splitting follows the Pascal39s triangle A10 Chromatography HL A101 Describe the techniques of gasliquid chromatography GLC and highperformance liquid chromatography HPLC 0 GLC o Used to separate amp identify small samples of gases and volatile liquids which can vaporize without decomposition o Procedure 0 HPLC Sample injected Vaporized in an oven Vapor carried through column by unreactive gas mobile phase Column filled with stationary phase usually long chain alkanes Components pass through column at different rates depends on affinity and boiling points retention time Chromatogram Detectors flame ionization or mass spectrometer Similarto GLC o High pressure used to force components through the column o Detection uses UV light o Can be attached to a mass spectrometer HPLCMS A102 Deduce which chromatographic technique is most appropriate for separating the components in a particular mixture 0 Stable volatile sample GLC 0 Nonvolatile or thermally unstable HPLC 0 For qualitative check paper and thinlayer 0 Preparation purposes column chromatography
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