Karteikarten
Spectroscopic methods of analysis
Karten in diesem Stapel (18)
- 1How do spectra arise?From the interaction of energy with atoms or molecules.
- 2What are common changes observed in spectra which are used to analyse molecules/reactions?Electronic changes (absorption or emission of energy) or magnetic changes (spin).
- 3How is molecular absorption different from atomic absorption and why does it use less energy?Molecular absorption uses energy to bend or stretch molecular bonds symmetrically/asymmetrically or exploit the natural variations, as opposed to exciting electrons. This requires less energy and the amount required and the size of the bonds is characteristic of the molecule or bond involved.
- 4What can a set of standards for calibration allow one to test?A property of an unknown sample.
- 5What is Planck's law? Give the calculation.The applied wave of energy in electromagnetic radiation (E) = ((Planck's constant (h) x the speed of light(c))/wavelength) = (Planck's constant (h) x frequency (v))
Speed of light: 299792458 m/s
Planck's constant: 6.626068 x 10^-34 m^2 kg/s
Planck's law states the energy is proportional to speed of light/wavelenth or Planck's constant multiplied by frequency. - 6Put the following types of spectroscopy in order of decreasing energy required: molecular vibration, nuclear spin, electronic transitions, and electronic spin resonance.Electronic transitions (such as atomic emission or absorption), molecular vibration (such as stretching/infrared), electronic spin resonance, and nuclear spin (NMR).
- 7What is happening to electrons during the emission and the absorption of energy?They are returning to a lower energy level or being promoted to a higher energy level.
- 8In flame photometry, what does the flame being applied to the sample do to it?The solvent is evaporated, the molecules are dissociated and the atoms vaporised (i.e. no longer ions in solution), and electrons in some atoms may become excited.
- 9Why might colour be emitted in flame photometry?Some atoms, due to their structure, have differences in electronic energy levels that are equivalent to the wavelengths of light in the visible spectrum. When electrons return to their original energy level, having been promoted by the application of energy such as a flame, the emission of energy is visible as a certain colour of light.
- 10What colours of light/flame are emitted by K+ and Na+ ions respectively?Lilac and yellow.
- 11In which ways is flame photometry able to be used qualitatively and quantitatively?Qualitatively - the colour emitted by the sample is representative of its atomic structure. Quantitatively - the intensity of the emission, in proportion to calibrated standards, is equivalent to the concentration of atoms in the sample, according to Beer's law.
- 12At high concentrations of a sample in flame photometry, there is negative deviation from linearity in a calibration graph (the proportional line curves off). What is the cause of this and how can it be resolved?There is reabsorption of emitted energy by atoms at high concentrations of atoms, which makes it look as though less energy is being emitted. This is resolved by diluting the standard concentrations.
- 13Name the five key parts of a flame photometer.The flame covered by a chimney, the spray chamber, the flow of gaseous alkane fuel and compressed air (adjusted to optimise flame size and temperature), a coloured glass filter to select the correct wavelength, and the photocell detector to detect the change in energy and give a reading.
- 14Give examples as to how flame photometry is used in healthcare, including which ions it is detecting.Na+ and K+ in blood serum, measuring malnutrition, dehydration, erythrocyte number, and heart function; Ca2+ in baby foods contaminated by the container tin; and Li+ in the blood of bipolar patients to determine the ratio excretion into urine to absorption into the body of medication.
- 15What is the difference in the mechanism between atomic emission spectrometry and atomic absorption spectrometry?In atomic emission spectrometry, energy is applied to a sample and the energy consequently emitted from it is measured qualitatively (colour) and quantitatively (light intensity). In atomic absorption spectrometry, energy is also applied to the sample, but the change in the intensity of the energy source (i.e. the flame) is measured to see how much was absorbed by the ground-state atoms. The wavelength at which the change occurs is related to the atomic structure (colour, qualitative) and the change in intensity is related to the concentration of atoms (quantitative, Beer's law).
- 16In a typical atomic absorption spectrometer, what type of lamp is used and how does this relate to the samples?A hollow cathode lamp is the light source and a separate one must be used for each element, as well as the correct flame temperature.
- 17What is the name of the piece of equipment used to reduce background light/radiation in atomic absorption spectrometry?A monochromator.
- 18What is an alternative piece of equipment to a flame photometer, used for environmental samples as it has greater sensitivity?A graphite furnace. This is a graphite rod with a small cavity to hold the sample parallel to the optical axis. The rod is surrounded by an inert gas to reduce oxidation, and a water coolant. It is electrically heated due to the unique structure of graphite and its high tolerance for heat, in four steps: dry (100 degrees C), decompose (400 degrees C), atomise (2000 degrees C), and pyrolysis (2300 degrees C).
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- (Scientific Skills) Karteikarten am Spectroscopic methods of analysis, erstellt von sophietevans am 15/05/2013.
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