Why do elements change colour when there on a Bunsen burner?

Answer 1

Flame colors are produced from the movement of the electrons in the metal ions present in the compounds.

For example, a sodium ion in an unexcited state has the structure 1s22s22p6.

When you heat it, the electrons gain energy and can jump into any of the empty orbitals at higher levels - for example, into the 7s or 6p or 4d or whatever, depending on how much energy a particular electron happens to absorb from the flame.

Because the electrons are now at a higher and more energetically unstable level, they tend to fall back down to where they were before - but not necessarily all in one go.

An electron which had been excited from the 2p level to an orbital in the 7 level, for example, might jump back to the 2p level in one go. That would release a certain amount of energy which would be seen as light of a particular colour.

However, it might jump back in two (or more) stages. For example, first to the 5 level and then back to the 2 level.

Each of these jumps involves a specific amount of energy being released as light energy, and each corresponds to a particular colour.

As a result of all these jumps, a spectrum of coloured lines will be produced. The colour you see will be a combination of all these individual colours.

The exact sizes of the possible jumps in energy terms vary from one metal ion to another. That means that each different ion will have a different pattern of spectral lines, and so a different flame colour.

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How is the test performed?

First, you need a clean wire loop! Platinum or nickel-chromium loops are most common. They may be cleaned by dipping in hydrochloric or nitric acid, followed by rinsing with distilled or deionized water. Test the cleanliness of the loop by inserting it into a Bunsen burner flame. If a burst of color is produced, the loop was not sufficiently clean. Ideally, a separate loop is used for each sample to be tested, but a loop may be carefully cleaned between tests.

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It is based on the observation that light emitted by any element gives a unique spectrum when passed through a spectroscope. When a salt of the metal is introduced into a Bunsen burner flame, the metallic ion produces characteristic color in the flame. Some metals and the colors they produce are: barium, yellow-green; calcium, red-orange; copper salts (except halides), emerald green; copper halides or other copper salts moistened with hydrochloric acid, blue-green; lithium, crimson; potassium, violet; sodium, yellow; and strontium, scarlet. The value of this simple flame test is limited by interferences (e.g., the barium flame masks calcium, lithium, or strontium) and by ambiguities (e.g., rubidium and cesium produce the same color as potassium). A colored glass is sometimes used to filter out light from one metal; for instance, blue cobalt glass filters out the yellow of sodium.

Answer 2

There may be an intermittent supply of gas, meaning a blockage or hole in the pipe or bunsen.