experiment 8: flame test

A flame test is a visual way of demonstrating the different frequencies emitted when an electron emits photons and moves from a higher energy state to a lower energy state.
Procedure

Sample of the element/compound is introduced to a colourless, non-luminous flame.
- In the experiment, we used ethanol, which was a coloured flame rather than a colourless one. This reduced the accuracy of the experiment and is therefore a systematic error.
As substance is heated, electrons become excited, as they gain energy the electrons can transition into a higher energy state.
Because the electrons are in a higher energy state, they are unstable. So they quickly transition back to their ground state, which emits photons with specific wavelengths (equal to the diff in energy levels)
Therefore, the photons have specific wavelengths, and the specific wavelengths mean specific colours are observed.
Since excited electrons can transition to their ground state in multiple stages, a set of diff photons of diff wavelengths can be emitted.
- This means a spectra of different wavelengths of light is noticed.
This test is only valid for some metals, as most non-metals emit frequencies outside of visible spectrum, and cannot be identified.

What can the test be used for

Ionic salts: simple ionic solids and metals can be used.
Because when heated, the metal ions and anions separate, producing emission within visible spectrum.

the test cannot detect low concentrations of most ions.
salt metal may not be excited by relatively low temperature of the ethanoal flame (magnesium)
salt may not be completely excited (diff colour being observed)
does not work with most non metals
ethanol and oxygen may get involved, changing the observed colour.
The brightness of the signal varies from one sample to another. For example, the yellow emission from sodium is much brighter than the red emission from the same amount of lithium.
Impurities or contaminants affect the test results. Sodium, in particular, is present in most compounds and will colour the flame. Sometimes a blue glass is used to filter out the yellow of sodium.
The test cannot differentiate between all elements. Several metals produce the same flame colour. Some compounds do not change the colour of the flame at all.