validation (emission and absorption spectrum) Flashcards
sodium
yellow
potassium
lilac
calcium
red
copper
green
limitations of flame test
- qualitative data only
- low conc of metals are hard to observe
- colours are subjective
- only a few metal ions can be detected
- mixtures of metals produce confusing results
spectroscopy
the study of the interaction between matter and electron magnectic radiation
what components of the salts is responsible for the colours observed?
metal ions
what assumption is made about the ethanol in the flame test?
that ethanol has a colourless flame and that it doesn’t effect the colour of the flame for accurate results
why must a clean watch glass be used for each test
so theres no contamination which can effect the result of the flame
Explain how the coloured light observed is produced
- When the metal ion in the salt is given heat (energy) the electrons becomes excited
- the electrons absorbs the energy and moves up an energy level (electron shell)
- this is very unstable
- when the electrons return to ground state the same energy absorbed is released in form of wavelengths (light)
Give a practical use of this type of the flame test
To identify and determine unknown metal ions
Often different colours are used to describe the same flame colour, e.g. lilac, mauve or purple for potassium.
Why might this be a problem?
Different people may have different opinions on the same flame colour. Therefore results are subjective.
Is this a random or systematic error? Justify your choice.
systematic because one individual will always identify and observe the same colour the same way in every test
explain how emission spectra provide evidence for electron shells in the Bohr model
- Bohrs model explained that these light emissions were able to identify that electrons in atoms can only be found at certain energies
- these engeries associate with the shells the electrons can be found in
why do we see lines in an emission spectrum are different colours
- when atoms are heated to an excited state & its valence elections jump to a higher energy level
- moments later as it returns to its original ground state
it will emit a colour of light with an energy that perfectly corresponding to the energy difference
does a sodium ion(2,8) and a neon atom (2,8) display the same emission spectra
no although they share the same electron configuration, they differ in charges in the nucleus and electrons
advantages of flame test
provides a quick analysis of the chemical composition of a sample
in AAS, what is the source of the energy that excites the atom in the sample being analysed
the light source that produces light characteristic of the metal being analysed
advantages of AAS over flame test
AAS:
- provides both a qualitative and quantitative test
- can detect elements in low conc
- is highly selective and is regularly used with mixtures
strontium
Scarlett
why do we see colour from the flame test
when unstable/excited electrons ‘fall’ back down to the ground state, they will all release the same amount of energy and therefor all produce the same wavelength of light
absorption spectra
electrons are able to absorb electromagnetic radiation and move to a higher energy level
Absorption lines are …
black
- the missing colours correspond to the exact quantity of energy required to promote valence electrons to a higher energy level
emission lines are …
coloured
- light emitted by the element can be separated into its wavelength components
