Why does a kitchen gas burner glow yellow when liquid comes in contact with it?

If you have been in the kitchen when your mother boils some water or milk, you may notice the flame of the gas burner turns yellow when liquid comes in contact with the flame. Did you know that there is chemistry at work behind this?

The story of sodium ions

A natural gas flame is yellow because of burning sodium atoms or ions. Water consists of salt dissolved in it. Common salt is sodium chloride. This is why you may notice that water that falls on the burners grill and evaporates leaves a white residue left on it. This white residue is salt. At the same time the sodium ionizes releasing photons that give the yellow.    
 
You may have also seen this yellow emission of sodium atoms in sodium lamps, which produce yellow light due to this reason. Even the tail of the Hale-Bopp comet is yellow for the same reason. 

The colour of a flame

The colour of a flame is also determined by the oxygen that is available to it. You may see that in your school chemistry lab the Bunsen burner may burn with a yellow flame. This is because of the incandescence of the fine soot particles that glow to produce the yellow flame. When oxygen increases, there is less soot released and the flame burns blue.

Refereence

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