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level: Level 2

Questions and Answers List

AAS

level questions: Level 2

QuestionAnswer
A SPECTROANALYTICAL PROCEDURE for the quantitative determination of chemical elements employing the ABSORPTION of OPTICAL RADIATION (light) by free atoms in the gaseous state. An analytical technique that measures the concentrations of elements. It makes use of the absorption of light by these elements in order to measure their concentration .Atomic Absorption Spectroscopy (AAS)
Atomic absorption is a very common technique for detecting __ in environmental samples.metals and metalloids
ELEMENTS DETECTED by Atomic Absorption.
Theory: Knowledge in atomic theory Ex. color flame from a lit matchstick The predominant color, yellow, is due to presence of __ in matchstick These atoms (at. # = 11: e configuration) in the unlit match are in __ state1 Na 2 ground
When atoms are excited by thermal energy, the valence e is promoted to higher level (excited state) Excited state of the atom is very __ and the e quickly drops back to the ground state to resume conditionunstable
Sampling: Requires __ to convert metal ions in soln. to atoms in gaseous state Ex. NaCl soln Na+ Cl- → NaCl → Na + Cl soln gaseous atoms atomsacetylene or other gas
INSTRUMENTATION: AAS1 Light Source 2 Flame 3 Monochromator 4 Detector
A hollow cathode lamp coated with the element being analyzedLight Source
INSTRUMENTATION: FLAME (AAS) Is usually __ providing temperature 2500 C __ may be used to provide 3000 C which are required to volatilize salts of elements such as __1 air/acetylene 2 Nitrous oxide / acetylene 3 aluminum or calcium
Used to NARROW DOWN THE WIDTH of the band radiation being examined and is thus set to monitor the wavelength being emitted from the flame, from the filler gas in the hollow cathode lamp and from other elements in the sampleMonochromator
It is a photosensitive cellDetector
AAS advantage:↑ sensitivity – only 0.01 % of the atoms in the flame are in excited state and emit light which is measured in Flame Emission method, the remaining atom (99.99%) are in the ground state and are unavailable in emission technique