aas and aes Flashcards
what is an emission spectra
a spectra produced by electrically excited vaporised elements and low-pressure gases. It is the spectrum of light given off by an element
what does the bright lines of an emission spectrum show
the light given off by an excited atom in the form of a photon in order to return to its lower energy level.
what is an absorption spectra
when light consisting of a continual spectrum is passed through a gas and shows dark lines. Shows when atoms have absorbed light.
what does the dark lines of an absorption spectrum show
indicate the particular wavelengths that has been absorbed
why do the bright lines of an element’s ES usually match up with the dark lines of AS
because the wavelengths of energy absorbed by an element’s electron to go up a higher energy level is the same as the energy emits to return back to its ground state.
what principle does the atomic absorption spectrum rely on
an element in its gaseous state can only absorb specific wavelengths of light.
describe the AAS experiment
A hollow cathode lamp made out of the same metal as the one being analysed in the test sample acts is going to be the light source. The test sample is going to be aspirated (sucked up) into a stream supplying the hot flame of the AAS. The flame makes sure the sample is atomised, meaning its atoms are freely moving. In this form, the target metal atoms can absorb the specific wavelengths of light radiating from the cathode lamp. A wavelength filter/prism then selects the desired wavelength of light from the exiting beam of light and the amplifier/signal detector determines the extent to which the wavelength has been absorbed (absorbance).
why does the cathode in the hollow cathode lamp have to be the same material as the metal being analysed from the test sample?
so that the lamp will emit light with a unique set of wavelengths specific to that target metal. When the light from the lamp passes through the vaporised test sample, only the metal being tested is able to absorb the light
how do you use the results from the AAS experiment to conclude the concentration of the target metal in a test sample.
using a calibration curve. It plots concentration of a specific metal against its absorbance. Once you have some known values along both axes, connect the dots into a straight line (like a line graph). You can plot the absorbance of the metal observed from the experiment and using the already plotted line, determine its concentration
describe the method of a flame test
a wire loop is first cleaned with distilled water or ethanol. Then, it is dipped into a paste of solution of the salt that is being tested. Placing that into the flame from a bunsen burner will excite its electrons in the vaporised metal ions of the salt. When they return back to their ground state, they will emit light (photon) of a specific wavelength, hence producing a specific colour. The colour indicated what elements are in the salt since each element has its unique emission spectrum
what are some errors associated with the flame test
human error or observational error. Colour is subjective and people’s perception of what colour something differs. It will also be hard to distinguish between similar-looking colours.
