Flame Colors as Chemical Indicators
Solutions on paper
Strips of paper towel were soaked in salt solutions and held over the flame of a laboratory burner. It was tricky to keep the paper form catching on fire, but for a brief time, you could catch the characteristic color of the metal ion. These are varieties of flames from a copper sulfate solution, but the yellow mixed in is presumably the flame color of the paper.
The potassium chloride worked very well with the paper towel strips soaked in the solution.
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| Strontium chloride at left gave the unmistakable red color. Copper sulfate above gave some variations in green. |
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Flame Colors by CO2 Transport
| Another way to observe flame colors is demonstrated by Scott Thompson. The chloride of a metal is dissolved in hydrochloric acid and placed in a shallow dish. Marble chips are added to the dish and it is placed below a bottom-vented laboratory burner. The reaction of the acid with the marble chips releases carbon dioxide which rises through the flame and carries metal ions with it. This sample exhibits the red color of strontium.
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